The way I see it, there's no "magic" to growing indoors. Plants respond to light, temperature, air, water, and nutrients; if you're having problems you must not be properly controlling all of those variables. It's not as easy as I've seen a lot of articles claim and most people are forced to make compromises, but if you can manage to create the right environment I don't see any reason you couldn't produce at the same level as a commercial greenhouse. Light and feeding are easily controlled, temperature and humidity can be tricky to get right IME.

Re cuttings vs grafted:
"This topic is for dissertation, there are many options. Sometimes cuttings are better."
Fair enough, I did some more research and decided it wasn't very clear-cut but all I could find were random articles with vague and unsupported claims. I'm curious if you know any good sources?

Alex, I believe in proof as well, the reason I didn't provide links is that rootstock compatability is a well researched topic which has been studied at a number of universities in the US. Specifically some in california. I commented on rootstock as there was a greenhouse in my area selling sick trees on rootstocks with known incompatabilities, recently, so it was a note to anyone reading to check compatability. (There were many people who returned to that nursery for help because they didn't know what they were doing wrong as their trees just died. I found out about it when a friend mentioned they could never grow citrus and then showed me the tag.) This isn't known for all varieties, and for some it's definitely a topic that can take more research, but for a lot of the more common varieties it has been studied for a long time. A great resource in this was written in 1986 by W.P. Bitters at UC riverside, and is titled Citrus Rootstocks their characters and reactions. The manuscript is available through UC riverside, and the same university has many good resources for rootstock compatability which includes a chart for the more common varieties and their rootstocks.

As for growing exclusively indoors, there are few resources, hence why I started the thread.

BonsaI, good job and thanks for all the info above))

"Fair enough, I did some more research and decided it wasn't very clear-cut but all I could find were random articles with vague and unsupported claims. I'm curious if you know any good sources?"

alexcm [z6a] Good research is difficult to do in an amateur setting. There are no good sources. I surveyed 20 experienced indoor gardening enthusiasts with above average knowledge. Nineteen said - cuttings or one / second / third stock no difference. Only one gardener knew the difference!

"1986 by W.P. Bitters at UC riverside, and is titled Citrus Rootstocks their characters and reactions"

bonsai_citrus_and_indoor_gardening Thank you. I read this book many years ago. It is good, but it does not answer all my questions. I was counting on you to show something new.

Alex, as I mentioned before. My mention of graft compatibility in this context was nothing more than a warning to look for common graft compatibility issues in citrus grafted outside of citrus growing regions, as it can be a stumbling block for some growing citrus if they don't know and buy a locally grafted tree on an incompatible root-stock. If you would like to know more about grafting, there are likely many more on this forum who could give you far more resources than I can, and it may be worth starting a new discussion for this purpose. Since I am limited on space, my interest in graft compatibility is mostly with regard to what you need to know when you're looking to buy a tree. I don't do my own grafting at the moment, and will further research the topic when I am in a place where I can. At the moment I cannot. This discussion post is mostly with regards to growing trees indoors, and compiling information from other indoor growers on what works/doesn't. As for the seed-grown/cutting/grafted argument, this is something that others may have more input on. My own trees are both seed grown and grafted, but the seed grown are all young, and not yet fruiting age.

Thought I'd pop in and add to this thread.

My fukushu has been doing extremely well with the hot sun we've had recently and has budded out and started to set a ton of fruit. (Photo is one branch).

I've also recently added a passion fruit to my collection, and it has bloomed. We'll see if it sets fruit in the next few weeks.

I've recently started giving my trees some occasional kelp meal for micros and it appears to have helped the weaker ones. My Nagami has yet to produce any blooms this year, but it is growing a lot of new branches. It requires the most water of my trees and tends to go dry very quickly, especially on hot days.

Not citrus, but an answer to a question I had a number of months ago, can I grow other kinds of fruit? The answer is yes. This is a Nancy Garrison Passion Fruit growing indoors in a pot right next to my citrus.

I've grown tomatoes indoors over the winter in a tent with a 600 watt HPS bulb. The setup was originally for growing pot but as I smoke less I don't have it going 24/7 anymore so I've gone the fresh tomatoes route over winter.

I get three years worth of growth keeping my seedlings inside a 5 gallon white bucket that is fitted with a ceramic socket with a 23 Watt daylight CFL

Ken, how are the indoor grown tomatoes? I've always been curious if they're as good as the ones grown outside in summer, or if they're a little more bland. Steve, I've seen your setups, it's really cool what you've managed to do. It definitely seems like a great way to grow rootstock fast for grafting.

I agree poncirusguy's white bucket is a good method for rootstock for cuttings.

I was wondering if anyone has had pest issues growing tomatoes in winter like that ?
Like the bucket idea. Going to put my fig trees in those white ones next year

Indoor grown tomatoes are just as good as outdoor. You just have to thin the herd a bit more. If you let every tomato grow they turn into cherries. Pests aren't a problem as I start the seeds indoors so they never get the chance for pests.

I posted found pictures here and they dissipated into thin air.

Steve, I've noticed that as well. I recently got a notification of a new comment on this thread, but it never showed. Not sure if there's something going on.

Ken, that's good to know. When I eventually have a bigger place I want to try to grow a few varieties indoors, see if I can keep them year round.

Mike, as for pests I've found that most plants grown exclusively indoors don't seem to have many. Pests are really confined to the ones you bring in. The only ones I find that can be problematic are fungus gnats, but those are usually brought in by a bag of soil that has them (best way to avoid this is to just mix mosquito bits into new soil when doing any potting/repotting. The BTI will just kill the eggs and they'll never show up.) or they fly in through the doors in August/September and you just have to make sure to sprinkle mosquito bits on the soil occasionally to make sure that they don't come in and lay eggs on watering day. I would imagine other flying pests in some areas might be a problem as well. Also, I quarantine all new plants to my indoor growing environment for 40 days by themselves so I can look for pests and then treat any and all pest problems before introducing them to the rest of my plants.

Have grown oranges exclusively indoors. Oranges take 7-15 months from bloom to harvest to ripen. It was an incredible amount of work. After that I started growing indoors and moving plants outside in the spring. Than built a greenhouse in the garage that used 100% artificial light to overwinter. This winter my pet project is a Gorilla grow tent.

Growing indoors you have to pay a lot of attention to the VPD. The further North you live the harder it is to control the vapor-pressure deficit.

Over-watering citrus is a bug-a-boo issue for people who use plastic pots. I water my citrus every day or every other day with a garden house outdoors depending on rain and zero issues. I use a potting mix which is sphagnum peat moss based with organic content. Clay pots drain really well outdoors. Indoors the VPD is so low with heating or air conditioning that the VPD sucks the moisture from the clay making it near impossible to over-water. In the winter I water every day indoors. With a good clay pot the water should take care of itself. The only caveat with watering is when someone gets carried away with fertilizer or just has a build up of fertilizer in their potted plants than all bets are off.

Biggest issue I have had growing indoors or in a greenhouse has far and away been insects, over-fertilizing, followed by not having enough light or lights or sunlight burning the plants. Once brought inside insects are near impossible to get rid of until the next spring when the plants go back outdoors.

My lights are Spectrum King LowPro Flower and Spectrum King SK 400+.

Never heard of VPD before, is that similar to humidity in the air?

VPD is vapor pressure deficit, basically it is the difference between how much moisture the air can hold and how much moisture is in the air. In cold weather the air can't hold as much moisture and so your air can be dryer depending on outdoor temp. Usually you would then humidify your air indoors so as to avoid the air getting too dry. It can be more of a problem in some places than in others.

VPD is the measurement of pressure in the atmosphere, which is measured and altered by temperature and humidity. The VPD in a grow room will determine how your plants transpire. This directly relates to your plants ability to consume nutrients and water.

If your VPD is too high or low, your plants will be over or under transpiring, leading to massive problems.

While vapor pressure deficit sounds scientific and confusing, it’s just a metric serious growers use to describe the combined pressure of air temperature, leaf temperature, and relative humidity.

Sun from a window, or grow light can easily raise leaf temperature (20F) putting the VPD in high stress levels which causes WLD. I found spring and fall easy times to grow indoors and winter and summer much harder because of the whole home heating and cooling systems.

That just my personal situation. Other people have different home construction and different climates and will have different experiences.

Hoping this isn’t something beginners have to worry about right now :)

I had gone away for a week and left the air off. I was worried because that week ended up being very hot but when I came back, the plants were thriving with lots of new growth. So I know they don’t love the AC but it can’t be helped. I’m really not looking forward to my first winter with citrus.

The AC isn't so much the problem, (I have both heating and AC in my house, in fact my sageretia theezans lives right under a vent and really doesn't mind it.) The problem is more that when you run heat or AC directly above a plant it can cause convection around the leaves and dry them out. One way to avoid this is to make sure that your plants aren't under any vents or that you close the vent near the plant. I'm lucky in that my growing area is downstairs which only has two vents for a large area, as a result neither the heating nor the AC are extremely effective. So long as your trees are adapted to their environment, you'll be fine. Just make sure they all sit above humidity trays.

Hi Annie, keep the room as cool as possible in the winter. The cooler the room the lower the VPD the less stress on the plant.

Should we give less light as well in the winter if we're using grow lights? I know we should water less.

Just want to thank Bonsai for starting this thread, the forum is lucky to have you! You've been a tremendous help to me and patiently answered all my many questions.

Hi Annie,

https://www.fourwindsgrowers.com/blogs/four-winds-growing/overwintering-your-citrus-trees

https://www.gardena.com/int/garden-life/garden-magazine/everything-you-have-always-wanted-to-know-about-citrus-trees-and-overwintering-them/

The answer to your question depends on whether you choose the Gardena a,b,or c strategy. It is completely dependent on your grow room and what the variables are.

In a home the roots will always gravitate to the temperature of the room. The leaves will be the temperature of the radiant heat from sun+grow light+air. When there is a difference of 20F or more between the roots and the leaves you will have WLD.

Water requirements are on a sliding scale depending on how much transpiration and photosynthesis are taking place.

Annie, well my hope is to compile some good information for indoor growers. I know there's a lot of info out there for indoor/outdoor but not much good info for strictly indoors. I've even been told by many that it can't be done. My trees sort of prove that wrong. Since I've learned a lot, I just try to help where I can.

As for reducing light, it really depends on your grow lights and how cold your room is. If your room hovers below 60, then you can probably do without the lights, if it's above 60, then you want to keep the lights on at least part of the day. I have an LED and a CFL and I've found that at least for my growing environment it can be helpful to extend my day a bit. But your situation may be different.

Heating pads are great for keeping the roots happy when ambient temps drop into the low 60's / upper 50's. Also check out brew belts from the home brewing industry. They work great and are low wattage. Then you can keep your lights on in the winter for better production without leaf drop.

Thought I'd drop in and share for those that are interested (ignore the yellow color, for some reason everything looks yellow and translucent on the camera under this guy's grow light), here is one of the clusters of fruit on my fukushu. It is also budding out again.

Also, and I'll drop in and share a photo when it's done dropping the leaves for this year, but I've noticed my edible fig bonsai drops its leaves and goes dormant every year for fall. Not sure if that's the poor heating in that room and the slight chill it gets, or if it's the lighting. Still deciding if that one will live in my growing area this winter or if I'll find somewhere else for it to reside until it starts growing again.

Update on the fukushu. After setting the last round of blooms into more fruit, it apparently decided it didn't have enough yet and started blooming again. This will be bloom #4 this year.

Anyone have any good recipes for preserving these guys? I find them a bit too sweet to stand on their own in preserves.

Photo shows bloom buds starting on the same branch that has fruit. These guys really do get fruit and flowers simultaneously, even indoors.

Anyway, I thought I'd drop in as I forgot to mention in my posts above that I do give my trees the occasional dusting of kelp meal (<1 tbsp for the big trees, far less for the little guys). And gnat season is upon us again, when growing indoors in a gnatty area keeping the pots in mosquito bits and DE until they go away becomes a must. Hopefully the cold weather will come soon and kill the swarms.

If they are too sweet for preserves, why not just eat them fresh.

Steve

I have a lot of them. So I hope to preserve a few. We'll be eating plenty fresh. :D

Thought I'd drop in and post an update and an observation: I grow all my trees in a loose and well draining mix. For the big guys it's been great, I might amend it with some extra water retaining media for any tiny plants or seedlings in the future, especially if I have a hot summer again.

We had a very hot summer this year, and while my big trees weathered it fairly well and didn't seem to mind, (my fukushu decided that I need lots of fruit, and come January/february I'm going to have more than I reasonably know what to do with.... honestly for as small as it is I did not expect it to be this loaded. If you want a little tree and a lot of fruit I might recommend one.), the seedlings seem to have just shut down. After worrying that they might not make it, I'm finally seeing some new growth on all of them.

That shows one of the tangelo seedlings just starting with some new growth. I did disover that by using some upside down bottles and a clear plastic cup I could better preserve the soil moisture on the really hot days and give them a little extra insulation as it cools down. It worked well to keep them alive. I do need to find a good way to do this for my rangpur as it really resents getting dry at all, and it doesn't like very bright sunlight, which I find odd. I might try building a mini grow-tent with a moveable shade cloth for bright days.

On the non-citrus front, I have discovered that not only do passion fruit actually set indoors, they will also obtain full color:

Can't wait to give this a try once it colors up. I'll drop in with an update on that when it does.

So, I said I'd drop in with an update on the passionfruit vine. As it turns out, yes, the fruit does color up fully indoors. I haven't cut into the fruit yet, to see if it really does have pulp, but here it is:

So, to answer the question: Can you grow passionfruit in a pot indoors? The answer is yes. Does it flower? Yes. Will the flowers become fruit? If you hand pollinate them, some of them will absolutely produce fruit. (My plant didn't have much growing time before fall hit, but it produced 8 fruits, the rest are only now beginning to get color). And does the fruit actually ripen indoors? YES!

A few lessons learned?

Don't use a tomato trellis. If I were to do this again I would definitely create a wider upside-down triangular style trellis with wire for the plant to climb on rather than twine and bamboo, and I would give it more space.

Get a wide and large pot, the 10 inch pot I used is definitely not big enough for it and the roots are already pushing the soil line up over the rim of the pot which makes watering fun...

Keep it as far away from any big plants as you can. It absolutely WILL find them, and if you don't watch, you will find it tangled in your trees within 24 hours. (I am not kidding on this one, I ignored it for a couple days this summer because I got busy with other stuff and came back to find multiple vines in my tree).

So there you have it, passionfruit will grow and produce indoors same as any citrus tree!

It was full of very tasty pulp. So it does fully produce fruit indoors.

Wow Bonsai, that's amazing. I would have thought passionfruit needed very tropical conditions.

I thought I would post my overdue update here. Here's my current collection -

1) Calamondin:

2) Thornless key lime:

3) Meyer Lemon in ICU:

4) Original Meyer Lemon (first citrus I ever got and accidentally tortured):

5a) Logee's Key Lime:

5b) And Logee's Key Lime part 2 (the tree originally came with two trunks so I potted the small one separately):

Some general information:

• These are all kept on windowsills with additional LED lighting except for the big Meyer Lemon which is in ICU away from the window but under it's own light.
• I use a 5-1-1 mix but adapted it to my own needs. Instead of perlite I use pumice.
• I fertilize with Osmocote Plus and Dynagro Pro
• When watering I bring them to a tub and water abundantly. The bigger trees have drip trays underneath but since humidity is getting lower, I will also have to do something for the little ones.
• Spray with horticultural oil or neem oil about 1-2 times a month as a preventative.
• Use wooden skewer or fingers to check if tree needs watering.

Random thoughts and questions:

I'm not sure why Meyer Lemons hate me. That's really the one fruit I've been looking forward to but the one I've struggled with most. #4 is very hardy though, it has not dropped any leaves since I last posted about it but it hasn't grown any either. The rootball is massive in relation to its size. There may be some tiny buds forming but it's too soon to tell.

I heard limes were most sensitive to the cold but both my key limes have been doing well. My little Logee's limes are both flowering again! I'll take off any fruit since they are both too small but what's that about? Does it seem like any of them need additional nutrients? And what kind?

What can I do about the 3) ICU Meyer Lemon? Aside from donating it back to California where it came from? It's just very sad and dropped a lot of leaves. I originally wanted to remove the water sucker (correct term?), the branch on the left but once the main branch lost most of its leaves I have left it alone. The 1) Calamondin also has a big water sucker on the right. Should I cut that off? Would that be a viable cutting?

What can I do about trees that are growing tilted sideways? I try to rotate them every few weeks but wondering if I need to do some shaping? I don't want to trim any leaves since they are small but should I try bending?

I've been using the DynaGro Pro with every watering but does anyone else hate the bottle it comes in? It's constantly dribbling every time I measure out a teaspoon and I've just about had it!

What else can I ramble about, it's gotten pretty cold in my area so I'm still trying to figure out the light/water/temp/humidity ratio since this will be my first winter with citrus. My apartment is set up so that each room is controlled separately so outside of the bedrooms the rest of the apartment gets cold at night. I'm just trying to keep everyone alive until it's warm again. Thanks for reading and wishing everyone luck with their trees.

Does the ICU meyer have a lemon on it? If so I might remove it to let the tree strengthen. Other than that I might just give the tree time and leave it alone. Watch for rootstock suckers if it's grafted and remove them, but othet than that it may just need time. My nagami looked like a horrible little stick when I first got it, and stayed that way for the better part of a year, then like someone had taken a bite out of the canopy, and now it is a large and beautiful tree. But it took years for that to happen. And even still it has scars all over it from the trauma it suffered. One growing season is really not that long. Also don't be too worried about some leaf drop in winter, with the shorter days and less light, some leaf drop is pretty common.

As for the sideways trees, you could try bending them with some wire, but I would probably leave them alone and give them time.

To raise humidity, an oversize drip tray is probably plenty for most places.

As for the temp drop at night, most citrus prefer a night drop of at least 10 degrees to do well.

And for some encouragement. My ever productive fukushu is loaded this year.

I'll try to get a picture of the whole tree when I move it to sweep up the fall mess of dead leaves and flowers that I've been too busy to keep on top of this year. This one always makes quite the mess, and moreso this year since it bloomed in clusters and probably had a couple hundred blooms... which are now all over the floor. It always drops quite a few leaves as it starts into a final growth spurt in the fall.

For Annieplantsny

There is symbiotic or interdependent relationship between Light (sunlight), temperature, water, humidity and nutrients. You have to consider how a Meyer Lemon planted in the ground would grow and than mimic those conditions and seasons indoors. If the symbiotic relationship between Light, temperature, water, humidity, and nutrients are working at cross purposes indoors the plant will die quickly. You can't fertilize like spring, water like summer, light like January, and provide humidity like a desert. Your grow situation as described and considering your location is like growing in the darkest days of winter.

A Meyer Lemon tree outdoors is fertilized from April-Sept. Fertilizer is than withheld from autumn through winter. Your adding fertilizer but the plant can't use the fertilizer because it does not have enough light this time of year. The fertilizer becomes toxic and you have leaf drop.

Many people overwinter citrus in a basement or garage where it is cool and use little supplemental light. They get away with it because the plant is basically dormant and the growth occurs mostly outdoors. In an apartment the temperature is always too high and the humidity is always too low for the plant to go dormant. You need a vapor pressure deficit that is stress free. That is almost possible in an apartment unless you have a grow tent where you can raise humidity.

Citrus are a lot like cannabis in light requirements. For an apartment I would recommend a grow tent with an LED rack light. When a citrus does not get the required light they are starved and they begin to consume themselves for energy. Your LED lighting gives off heat. Should not raise the leaf temperature more than 10F. Use an infrared thermometer to confirm you are not placing the light too close or too far away.

The LED industry uses 10,000 Lumen per square foot as a benchmark for natural sunlight. If you can get 5000/sq foot indoors you are doing pretty good. This picture below is with a spectrum king Low Pro Flower plus. The light produces about 102,000 lumen. It is the equivalent of a 1000W Double Ended HPS Fixture. Had to turn the light down about 20% to keep the ballast running cooler and in turn that dropped the surface temperature of the leaves to about 10F above ambient. Currently running at 65 RH.

When you do take your plant outside give it the TLC it needs and fertilize with a proper citrus fertilizer. They have specific macro and micro nutrients.

Another way to visualize the growing seasons is to compare to swimming in a lake. If a lake is 50F but the ambient air is 80F than the swim is not that enjoyable. The same goes for your plants. If the pot soil is chilly and the leafs are burning up under artificial lighting the plant won't enjoy the experience. All the variables have to work together.

Citrus are heavy feeders when they are growing. They like lots of compost.

Citrus, Cacti, Succulents, Photography · More Info

Citrus, Cacti, Succulents, Photography · More Info

Hi Bonsai, yes the ICU lemon has a lemon about the size of a golf ball on it. I know I should take it off but I was so looking forward to my one lemon! I do see some tiny leaf buds on some of the branches so I hope it’s in recovery however long it takes.

Giving them time and letting them grow is fine, I just wanted to know if there was anything I could be doing or not doing. Those fukushu look large for kumquats, unless I’m misunderstanding scale? Love seeing your trees Bonsai. Thanks!

Lemon Lime, thank you, you’ve provided really valuable information. I’m going to respond more when I’ve gathered my thoughts, you’ve given me lots to think about. I had some of my trees in terracotta until recently but switched to plastic because the terracota was getting so cold on the windowsill.

Just one pressing issue though, since I’m not keeping the trees dormant indoors, can I go ahead and apply more Osmocote Plus? It has been over 6 months since I last applied it.

Lemon lime, while I would agree with some of what you have said, for example dialing back on the fertilizer (I didn't catch that) as growth will slow down. I would disagree on a grow tent. My own trees grow just fine without it and I know of a few others who do the same. Citrus don't require the same environment as higher humidity plants, and, depending on the apartment, humidity can be more than adequate. Annieplantsny indicates that the apartment is zone heated/cooled and that the rooms with the trees can get rather cold. This would tell me that the trees are in slower growth which would indicate less fertilizer. Humidity trays should be just fine.

Annieplants, yes the fukushus are VERY large for kumquats and this little tree is odd in that it prefers to grow huge fruit. They'll double or triple in size before they're ready and are regularly as big or bigger than a mandarin orange. I love them. You definitely want to dial back fertilizer in winter, especially if their growing area gets colder. I don't usually apply their granular fertilizer again until february when it begins to warm up in my area and the days get longer. In my case I know if the plants are semi-dormant because my fig tree goes into full dormancy every winter.

Here are sample photographs of my results using a grow tent.

Anyone anywhere in the world can duplicate my results over and over again using similar quality cannabis rack lighting, a grow tent, humidifier, infrared thermometer, and VPD chart

Some greenhouse, basements, sunrooms, or garages may naturally have the correct VPD to grow citrus. Most living rooms or apartments don't have the right VPD. If VPD is wrong indoors for long enough with poor light, failure is certain.

No two people have the same variables indoors so most advice can neither be qualified or quantified. You have to experiment and see what works. What works in one latitude may not work in another. The beauty of the grow tent is that you can manage variables indoors that would otherwise be impossible to manage.

Your trees are very nice, and I won't get into this more than to post the following source: https://irrec.ifas.ufl.edu/flcitrus/pdfs/short.course.and.workshop/citrus_flowering_97/Davies-OverviewofClimaticEffects.pdf

I hope the link works.

Everyone has a different climate and different experiences, and I respect that. But there are also many different environments where citrus grow and thrive. Each person has to figure out, for their own circumstances, what works for them.

Interesting article. Have used it many times. It does not qualify or quantify how to grow citrus indoors in an apartment.

It takes more than dry or wet; hot or cold air by itself to grow citrus. The common thread is sunlight which is not the same quality indoors.

Growing citrus indoors is possible but can’t be qualified or quantified easily and that is why there are no unique books on the subject.

https://www.gardenista.com/posts/5-secrets-tips-grow-indoor-lemon-tree/

Yes, growing environments are different. LLO, I will put this out there, I tend not to want to engage you in these types of discussions as you tend to throw out the same articles and figures and discount the thoughts of others. I have read the gardenista articles, it's not my favorite resource for a lot of reasons but mostly because it tends to be overly pessimistic and somewhat inaccurate in some of its assumptions. I have been growing citrus exclusively indoors for several years. Before that I assisted a family member with their greenhouse grown citrus for about 15 years. I get a harvest annually of fukushu kumquats and now passion fruit that's always very good. I hope to get a harvest next year from my Nagami if it's finally healthy after being thrashed by the greenhouse that I got it from. It's taken years. According to the article I posted, citrus do fine in humidities around 20%. For a home to be healthy and the inhabitants to not be suffering ill effects of low humidity, the humidity needs to be around 30%. I have gotten hands on experience this year with what low humidity can do to both an individual as well as a plant when a large water leak led to a remediation company running 4 industrial dehumidifiers in my home for two weeks and bringing the humidity down to very near 0. It was difficult to keep the citrus alive and they're all still recovering from it. My kid's seed grown mandarinquat was the only unlucky plant and it was, unfortunately, in a bedroom which was inaccessible until after the humdifiers were removed. I can tell you that we all suffered negative effects long before the trees did, and the trees were all saved by keeping them watered and their trays full. I mention this to say that if your citrus are struggling from low humidity, you don't need to humidify THEM, you probably want to figure out what it will take to fix your home humidity as that's going to be a worse problem for you.

Your anecdotal example in your own home shows the adverse affect from a drop in humidity indoors. You have made Mario's point. If your going to contradict what Mario Vega, a nursery specialist at the Conservatory of Flowers in San Francisco’s Golden Gate Park, said than please provide evidence other than anecdotal. Comparing growing citrus in the desert to an apartment is a gigantic hyperbole. Citrus grow in low humidity deserts because of strong photosynthesis, cultivar, specific root stock and deep roots. The sunlight in the those regions would be about 50-100X the strength of a windowsill in NY in December.

I always post pictures of my results in my idea book so people can judge for themselves. I share my complete methodology, back up comments with scientific research papers, or back up points from citrus citrus nurseries, or UFL. Have family who grow citrus in Florida but I learned how to grow citrus in Toronto Canada which is zone 5 in USDA terms. I have grown sweet oranges indoors 12 months of the year, outdoors/indoors 8/4 months, growing in a living room 12 months, grown in a garage greenhouse with artificial light, and currently growing in a grow tent.

Here is my current methodology. I use full spectrum cannabis lighting because the sun at this latitude is not strong enough. I recommend a vegetative VPD when you have a new flush. I than shift to a flower VPD for fruit and flowers. Lights on about 16 hours per day off for 8. Distance the light far enough from the canopy that it raises the light temperature by no more than 10F. I use deluxe potting soil which contains sphagnum peat moss, compost and forestry products. Citrus are like roses they love compost. Maintain the RH around 60-65. Temperature about 73 F in lower canopy. About 83F closest to the lights. Us a humidifier in the tent to add moisture and a dehumidifier outside the tent to remove excess moisture. Citrus have specific micro and macro ingredients. I use various brands but always specific to citrus. Indoors I find soluble works better than dry fertilizer. I don't recommend fertilizing indoors in the winter unless you have strong light to create enough photosynthesis for the plant to use the fertilizer. Too much fertilizer builds up too fast and becomes highly toxic. Fastest way to WLD is to winter fertilize, grow in a stressful VPD, have wild swings in temperature or humidity or pretend light does not matter.

Growing citrus indoors is like opening a lock. There are millions of locks with millions of keys. You have to know what type of lock you are working with and what type of keys may open that lock to get started. If the key won't turn than the lock won't open.

Grow tents are part of a multi-billion dollar industry that is growing at a (CAGR) of 24.8%. There is a cost component of grow tents but the results if set up correctly are indisputable.

Here are two examples where the humidity is almost double and both examples are an identical growing condition.

RH=35% F=59 degree VPD=1.11 (vegetative)

RH=65% F=77 degree VPD=1.11 (vegetative)

Here are three examples with identical low humidity where the growing conditions range from flower to high stress to dangerous.

RH=35 F=68 degree VPD=1.52 (flower&fruit)

RH=35 F=82 degree VPD=2.46 (high stress)

RH=35 F=88 degree VPD=3.09 (dangerous)

Done correctly the VPD takes into account the leaf temperature. In a window or under a grow light the leaf temperature can spike 40F easily.

Out of the above 5 examples only RH=35 & 68F would be suitable for a living room. In this example the dew point temperature would be 25.5F. If the outdoor temperature is very cold it is likely you would have moisture running down the glass windows.

This is why growing citrus indoors in Canada is not very practical because the outdoor temperature in the winter is too cold to maintain the correct VPD in your living room.

To fertilize or not to fertilize was asked. The answer depends on: how much NPK is in the soil already, the season, type of potting soil, indoor vs outdoor, pot vs in ground, size of trunk, strength of grow light, how much NPK is in the soil, and whether you have a mineral deficiency, and last but not least the type of fertilizer, water soluble, fast release or slow release. At the point where you have added too much fertilizer you will see leaf drop the next day and a change of leaf color. Citrus fertilizer is designed for pots outdoors or plants in ground. If you are growing indoors 12 months of the year you have to read between the lines to reduce because the light quality and growth will not be the same. Grow scripts has some good products. J.R Peters Citrus formula is another good option.