Peter, I asked the same question two years ago on this Forum and was assured that Low-e glass had no effect on plant growth. I was considering installing such a greenhouse window to replace one in the kitchen flooded with brilliant sun six hours a day. This would allow me to grow tender herbs during the winter plus geraniums, etc. Just a quick note to say that I am a retired pro able to grow and propagate most any plant.

My observations on the subject:
1. Basil and other tender herbs refused to grow. Died.

2. Flowering plants such as geraniums put into the window in full bud did bloom and then refused to set more flower buds, gradually weakened and were removed.

3. A 4' Norfolk pine placed in the window greenhouse two years ago is alive, healthy and has not shown any sign of new growth.

4. Non-blooming tropical/semi tropical foliage plants that require indirect light in the outside world seem to remain healthy with very little signs of growth. My one exception has been Crocodile Fern (Microsorum musifolium) which thrives in almost any situation.

5. Plants are happier in clay pots, not plastic.

Tapla, here is an experiment for you. I have found the Low-e light seems to encourage rooting cuttings both in water and soil. As this is the time of year to take many cuttings...insert a few cuttings dipped in rooting hormone in a large pot. Cover with a piece of Low-e glass propped up a bit for air circulation and place pot in morning bright sun, afternoon shade. Try some variations of this for your own interest. Check in with your observations as you play with idea.

Nan - while your plants may have succumbed to less than advantageous light conditions, you cannot logically blame it on low-e coatings until you've eliminated other possibilities. In trying to eliminate them, I'm certain you'll find your cause(es) on the shortlist of cultural conditions that need to be checked off first.

My grandpa went outdoors in the rain without a coat & two days later he took sick and died; therefore, walking in the rain will kill you.

The general idea behind logical fallacy (this is not a derogatory term, Nan) is that it is an error in reasoning to conclude that one thing causes another simply because the two are associated on a regular basis or over time. More formally, the fallacy is committed when it is concluded that A is the cause of B simply because they are associated on anything like a regular basis. The error being made is that a causal conclusion is being drawn from inadequate evidence.

I already provided the science behind why there is no problem using low-e glass in greenhouse situations, so I'll answer anecdote with anecdote. We probably built 15-20 greenhouses or sunrooms last year alone that had low-e glass. You KNOW I'm a plantsman, and of course, the people who had the greenhouses/sunrooms built were willing conversants with me about many things plant related. I have occasion to talk to these people as repeat customers, and not once has any of them mentioned diminished plant growth or growth that didn't exceed their expectations. My personal observations also bear this out. Most problems I have seen are temperature related (your problem?) because of increased solar gain and warm soils, related to photo-intensity (too much light), poor watering practices, or from accumulations of salt in the soil due to poor soil and too infrequent repotting practices.

IOW - you need to look to a cause other than low-e coatings for the source of your plant's problems.

Take care.

Al

Sorry, Tapla. I will not accept the premise that my growing practices have inhibited plant growth in my Low-e window greenhouse. At this point the OP has two very contrary opinions on the subject. Actually, when I began to encounter problems I started growing the same types of plants in another regular, non Low-e glass window facing in the same direction for comparison and those plants are thriving, sending out excellent new growth. In both situations the cultural conditions are exactly the same. All I can do on the subject is report my experience.

Of course your growing practices, and particularly the cultural conditions you're able to provide, inhibit your plant's growth. I know MINE do. "HEY OUT THERE! IS THERE ANYONE WHO THINKS THEY ARE PROVIDING PERFECT CULTURAL CONDITIONS FOR THEIR PLANTS?" Of course there isn't - it's impossible. Besides, we're all flawed as growers - you and I included. 'Perfect' is God's work. We can only reach for excellence.

Let's look at it from a different approach. Low-e coatings reduce the amount of the visible spectrum transmitted (through glass) by less than 5% (it reflects heat - not light). The visible portion of the spectrum is the part that is necessary for plant growth. This leaves the onus of explaining how low-e coatings affect YOUR plant's growth to such a degree (when it affects no one else's) on you.

If your windows have other pyrolytic coatings (reflective coatings other than low-e) or are also tinted, it could have significant impact on light transmission, but again, a simple low-e coating does not, and will not have any noticeable impact on plants grown under equal conditions but not receiving light through glass with a low-e coating.

If I may, I'll mention that I am called on almost daily by engineers, architects, contractors, builders, and homeowners to offer opinions or cite figures on effects like visual light transmittance, shading coefficients, relative heat gain resulting from photo-transmittance ..... of various glass and glazing products, and have been providing this information and opinion (and getting paid for it) for 32 years.

I illustrated why the logic in your belief is flawed, but I cannot stop you from believing what you wish. That you refuse to accept as the reason for your plants' poor performance something other than a simple low-e coating, namely another cultural condition or a combination of several, is your choice; but, what you 'think' and whether YOU accept it or not doesn't change applied science any more than wishing real hard would.

The things I stated are easily verified facts, not theory or guesswork. It's not the low-e coating. Sorry.

Al

Although I am a bit late to this discussion, and it may already be dead, I have to agree with Tapla that pretty much all evidence and research indicates that LowE coatings do not negatively affect plant growth. In fact, some studies have indicated that LowE coated glass actually improves plant growth over clear, uncoated glass

As tapla noted, LowE coatings are designed to block heat in the IR spectrum. Depending on the type of LowE used, there may also be some level of light blockage at the far red end of the visible spectrum as well.

LowE coatings also block a certain level of UV, again the amount of UV blocked depends on the coating.

One comment though for Tapla. You referred to "pyrolytic" LowE coatings, and in the US the vast majority of LowE is sputter and not pyrolytic. Probably only about 5-10% of LowE coatings used in the US are pyrolytic. This doesn't affect anything in your reply of course.

To the several folks that have replied to my request re. low-e windows: Thanks so much!!

I have two friends both of whom are contractors, one of whom is my advisor on all things re. my house, the other does the work! Neither had a clue as to the effect of low-e windows on what's inside the house. We now have a much clearer understanding.

Peter

I thought Basil liked low light and doesn't last the whole year going dormant (dead) in the summer months.
Could there possibly be a different temperature in that corner of the house, my cat even knows the coolest spots in the house, and that is where she sleeps. What about the air circulation in that spot, or air temperatures I have plants growing side by side, and they arn't the same.
I also have had professional training, and have been growing plants for over 30 years. I still don't know why some flourish and the others don't even in my greenhouse, I have some spots that are hot and some cooler. Still learning.

Basil requires a lot of light to survive, more light than most houses have. It is also not an annual, but tender perennial where it is from, and can be kept over winter if trimmed. It will live for years if greenhouse grown, however will die in a house setting regardless of the window used.

I once argued the same point you're making, Mentha, but I got corrected, so looked into it. I found a very few basils (2?, 3?) are perennial, with a large majority being annuals.

Al

Al,
I don't find that to be the case. They grow as perennial here in CA. I put a cloche over them in the winter and they live just fine. The trick is to dehead the flowers. Most people just give up on them, much like poinsettias. They can also be propagated really easy by cuttings. It's mild enough here that I can grow tomatoes into winter, and only have to cover them in deep winter months, January & February. Basil is no different, but it must be outside most of the summer.

I know, I know ..... that's exactly what I said, too; but when someone argued with me about the point, I went looking into it, and I found that I couldn't support what I had said. I definitely know the difference between annuals and perennials - you'll find me advising folks often that just because you grow tender perennials AS annuals (Coleus, snapdragon, Impatiens ... yada yada ... it doesn't make them annuals, so that's not the issue. You may very well be growing perennial varieties - no argument there at all, but if you look into it, you'll see there are lots of basils that are listed as TRUE annuals and only a very few (2-3)listed as TRUE perennials.

One of the reasons I know this is I did some pretty extensive research when I was considering the best species to add to my group of herb bonsai.

Al

Al,
I'm going to still argue they are perennial. Granted some basil is easier to keep up like holy basil and thai basil, but they are still perennial regardless of whether someone can grow them as such. A few years ago, when I had over 100 herbals, I was also researching mint and mint cousins, thus my name 'Mentha'. I had over 50 mints and 20 or so basils. I found most basil is considered a tender perennial and only they will grow as such. either Mission San Miguel or Mission SLO has a sweet basil plant which they've had for 15 years. If you look at herb suppliers they all argue that most basil is perennial, I'd say all but only a select few aren't.

Regardelss, my point was you can't use basil as an indicator whether the windows are good for growing plants since basil will not grow inside unless you really have a green thumb and know what you're doing. you almost have to have wall to wall windows and a southern exposure to boot.

Maybe the plants that didn't do well in Low-e window liked the extra heat? Just a thought...

I have some now and again =D

Down here, my basil goes crazy, so I can't even keep them as 'annuals'. I must keep the crops coming, like I do with my corriander/cilantro. Bolting occurs quickly!

Al, what would brownish reflective colored tinting do as far as plants are concerned? I understand the blue part of the spectrum...

Shannon

Is it reflective? so that it looks like a mirror from the outside during the day, or is it just tinted?

Al

Reflective. But still not enough. It's hotter than heck in that room in the mornings!

Looks like a mirror from the outside during the day, opposite at night...

Shannon

How much light this window arrangement eliminates is considerable, and variable, depending on whether it is a glass coating, heat mirror, etc., and whether their use includes conjunction with a tinted glass product. I can say though, that I wouldn't be surprised if they eliminate more than 60-70% of available visible light.

Al

Kari - Respectfully, I must say that what you are saying is simply and unequivocally WRONG. Low-e coatings reflect heat and almost NO light, so it DOESN'T keep the "hot sun" out in the summer. If you are having problems with your windows, if it seems noticeably darker in your home, it's NOT because of the low-e coating; rather, it is because of some other feature included in the package ASIDE FROM low-e, such as tinting or heat mirror between the lites of glass. The shading coefficient of low-e is extremely low, while other treatments like tinting, heat mirror or reflective coatings, or these two treatments in combination can reduce light transmission by 70% or more, but low-e has no noticeable effect on visible light transmission, the part of the spectrum plants use.

Al

... pardon please? - I should have said the shading EFFECT (not coefficient) of low-e is extremely low.

Al

I'm looking into replacing some windows because of the tax credit this year. Tax credit requires low-e of 0.3 or something like that. Reading manufacturer's literature, I found some claims that their windows reduce UV light by 75 or 85 or so percent, so will save furniture, flooring, and fabrics from fading or changing color. It occurred to me that if this is true, it might not be good for growing plants.

So I searched here to see if Al might know about this. I am not surprised that he does. :)

Here's an example regarding Marvin's Infinity replacement windows:

"Low E II reflects heat back to its source, so summer heat is reflected outdoors and indoor heating in the winter is retained. Low E II also blocks up to 84% of UV rays to reduce fading and damage to upholstery and carpet."

and

"Our optional LoÃÂ�-366 glass provides increased performance for high sun exposure locations. This top-performance glass is formulated to reject solar heat while letting light in. With LoÃÂ�-366, light and visibility are maximized, while up to 95% of the sun's damaging UV rays are blocked.

Optional LoÃÂ�-366 glass qualifies Infinity windows and doors for the Federal Stimulus Tax Credit. To learn more about how to get up to $1500.00 in tax credit, visit our Tax Credit page."

I am guessing that this UV blocking would not be good for growing plants. I would love to hear Al's thoughts on this.

Here is a link that might be useful: Marvin Infinity glass options

The entire impact of UV radiation on plants is not clearly understood, though some forms of UV light are harmful in several ways, just as they are to animals. I know of at least one study that indicated high UV levels actually activated some defense genes that helped a plant fight off its attackers. There are different types of UV light as well, and blocking certain types can leave a plant more prone to fungal issues.

I generally look at UV light as an insignificant portion of the spectrum, as far as plant growth/metabolism is concerned. The visible portion of the spectrum is much more critical to plant growth, particularly the red and blue portion. A more important consideration for growers and their plants would be the fraction of light from the visible parts of the spectrum that actually pass through the glass and strike the plants, and in what wavelengths (colors).

The windows in my business are tinted blue - I wish they weren't. because they reflect most of the blue fraction of the spectrum, which is very important to vegetative growth. My plants do grow a little leggy at the office, but the Ford Blue glass in the insulating glass units allows only about 40% of the visible spectrum to pass, and very little blue light. :-( Still, other than being a little stretched out, the plants seem to grow quite well & are perfectly healthy. I credit a good soil, favorable watering habits, and a sound nutritional program for ensuring light is the only limiting factor of consequence.

Al

I may be too late to add my two cents, but here goes.... I grow many orchids, in my house, in front of SW picture window and NE picture window (with no supplemental grow lights.) In the past, I have had some plants burn, up against the glass and had trouble growing without sunscald, unless I used sheer curtains (which I hate). I also had issues with chilling near the glass, during the winter months.

We had low e windows installed. Double pane with argon gas, no addl tinting. My plants are much happier now. While I'm sure they may miss some of the extra heat in the winter months, they no longer scald and I can have them right up to the window without scalding and without chilling them.

My vote would be to get the new windows but make sure they do not add any additional tinting.

You're not missing any winter heat, Susan. Low-E products allow light to pass through, so passive solar (heat) gain is about the same (only slightly less, but not a significant amount), but they reflect heat. In winter then, the heat trapped inside your home is reflected back toward the interior of your home and your plants.

That you no longer experience photo-oxidation, aka sunburn (sunscald is something usually associated with freezing conditions and outdoor trees - occasionally fruit, too), is a good indication that the low-e coating has somewhat reduced the amount of light transmitted. This is probably favorable for plants that don't prefer full sun, but a small step backward in terms of how much light passes; this, in consideration of plants that DO prefer more sun. Still, it sure wouldn't stop me from upgrading to Low-E/argon or krypton ..... if I didn't already have it. ;o)

Al

I am way late to this conversation, but here and now in 2013 the Low E coatings now required to produce an Energy Star rating will certainly affect plant growth. To achieve an Energy Star rating here in the state of CA you need to have a window with a U-factor of less than .35. To achieve that type of U-factor it requires 3 layers of Low-E coating which will give you a VLT (visible light tranmittance) of .49-.53 on average depending on the glass manufacturer. That means you are cutiing down approximately 1/2 of your visible light, which certainly has an effect on some plants. There are some plants that will continue to grow but there are many that will not live without more unfiltered lighting. I don't care what your window sales guy tells you (I happen to be one) it does and will effect the types of plants that will thrive in your house.

it does and will effect the types of plants that will thrive in your house. That's the thing about any sales person, they also know how to mis-represent the product they sell.
If not successful in misrepresenting there items they wont get dinner on the table every night.

Okay if to mean plants will thrive in windows with the type of glass of a certain type explain why plants also thrive with a lesser form of glass that also exist.

Tapla: A little off topic, but I would appreciate your expertise on this question. I am repurposing two Dual Pane / low E picture windows on a solar water heater collector. Would it be best to reverse the window for maximum radiant heat exposure to the collectors?

I can't answer specifically w/o knowing whether the low-e coating is/was on the 2nd or 3rd surface (with the first surface being the surface exposed to the exterior), but in applications like yours, where you want to trap heat, the low-e coating would go on the 3rd surface to maximize heat reflection. That would be the inside surface of the inboard lite of glass.

If you can get at the inboard surfaces w/o compromising the IGU's seal, an inexpensive continuity tester will tell you what surface the coating is on. If you live in an area where heating costs are greater than cooling costs, the coating SHOULD HAVE BEEN on the 3rd surface, but there is no guarantee that guideline was followed - especially in residential applications.

Al

it is on the #2 (inside of surface of exterior pane)

Spin the unit so the low-e coating is on the 3rd surface to trap the most heat inside the collector.

Al

I am a glass guy, not a plant guy but . . . Another possible missing factor: the "heat" blocked by LowE coatings is actually IR light. While not visible light, it could be possible that some plants need it to thrive. A quick Google pulls up problems with flowering plants blooming.

Al, thanks so much for your input on this thread that I shouldn't be afraid of low-e affecting visible light for my greenhouse plants, that it only cuts off 5% visible light (generally)! How is U-value related to UV light or visible light if at all? Is U-value = 1/R, simply an insulation value so I shouldn't worry about it affecting plant photosynthesis/metabolism)? We'll get double pane glass, not triple pane, due to cost. Please comment on how U-values affect plant growth. Summer 2015 we'll build our new house and attached greenhouse. Greenhouse window selection is daunting with legodude1970's 2013 comment that U-value less than .35 can be bad for plant growth, so does U value also block visible light? Or might legodud1970's windows have some tinting he's not revealing in his post? Have windows really changed that much from 2010-2013, and now in 2015? How is U value related to E value? Are they always intertwined, or depends on manufacturers processes (such as sputter vs pyrolytic vs other process)? Our greenhouse will never freeze, stay 55-65 degrees F at its coldest, have tomatoes, peas, microgreens, kale, watercress, herbs, flowers year-round and some tropical plants in Colorado at 9600' elevation. I've been talked out of triple layer polycarbonate and into glass due to aesthetics, but much costlier. PPG website says consult a horticulturist, but I simply want to know what type of light comes through their glass, and velux, pella and milgard do not provide this info. Perhaps U-Value is simply insulation value (like 1/R) and I should only be worried about the low e value, not the U value, for plant growth? Please help. Thank you very much!

I have quite a few Jades, as well as a Norfolk Island pine, and a large ficus alii growing in my sunny dining room. The light is coming through low-e glass, and all of them have grown just fine for years. The jades lose a lot of their nice summer coloring, but I am in Wisconsin, so sunlight is in short supply for the 6 months of winter here. Quite a few of my jades tend to put on a lot of growth over the winter too, through the low-e glass. I won't argue the science of the glass, but I'll argue the ability to grow plants through it.

Joe

Thanks, all, for the in-depth discussion on this issue. I'm so happy to see recent posts. My husband is a professional gardener and so of course we will also want plants in our new-construction home. We are considering installing two walls of glass bi-fold doors in Texas (think HOT for 4 month) opening up our great room to our front and back gardens which has me researching plant growth and LowE windows. I came across an interesting paper on the colors of light needed for plant growth, What light do plants need.pdf - Heliospectra. This paper includes green light as a necessary component for a different process than photosynthesis called "Photomorphogensis", which seems to be relevant to plant growth. Perhaps the absence of this spectrum of light is what has contributed to the absence of plant growth discussed above. Again, many thanks for the discussion. This has been quite helpful.

My orchids have bloomed every year since 2001 when I received the first one. I have eleven none newer then five years, several different varieties. I had low UV windows installed in October. 2014. The one plant that had already set buds, bloomed in February 2015 the others look healthy, but did not set buds or bloom. I usually have continuos blooms because of the variety, from January through October. I am so sad about my orchids, but happy that the house is a bit cooler without air conditioning. I did not change any other variables for the orchids, same fertilizer and water regimes.

We are renting an apartment that I believe has low E glass. At some point I was enlightened to that fact that low E, while preventing heat gain, also prevents fading of fabric and carpeting in your rooms. If Low E's purpose is to deflect heat then light would fade fabric.

We have east facing windows that my plants are right in front of and since I brought them inside they have very little growth and what growth there is appears spindly and not healthy. The new growth on rosemary has powdery mildew? Orchids are wholly failing to thrive, also an azalea that I've bloomed for over a year is fading fast. The exception to this scenario is a geranium that I pulled from a dead bouquet from a friends house, the stem was still green, and stuck it in a pot, that is growing!

I have two large bathrooms in which I thought I could install grow lights and run the shower for humidity but the fools that built this place neglected to put electrical outlets anywhere except the sink area!

Now, what to do? Throw everything out instead of waiting for it to do?

Vicki

Hi there! I have a question about Argon. Is argon which leaked from window into home can kill human? If yes, how much argon can kill human? Is argon from window pane enough to cause death? The reason i am asking this question is, i am about to change my old window to new one with Low-E+Argon, and if my kid accidentally breaks glass pane from inside home, is it safe or not?

Thank you

Tamir Gantumur

From Ulan-Bator, Mongolia

Argon is a noble gas, non-toxic, and heavier than air.

Broken glass is much more dangerous. =)

thank you for reply, but question is what if for any circumstances we break window and argon leaks out from window into home, is argon will cause a death, if yes how much argon can kill a human? or is argon which window manufacture put in it, not enough to cause a death?

Thank you

No matter how many windows you break, you will not die from Argon inhalation.

I live in California. I purchased Milgard dual pane windows a few years back. They have the UV filter to protect furniture, etc. Before purchasing the windows, I was able to grow beautiful African violets by my kitchen window. Since having the new windows installed, I can't get a single plant to grow there. So, from my own experience, the filter on my new windows does not allow plants to grow at all.

https://www.andersenwindows.com/windows-and-doors/options-and-accessories/glass-options/

So much misinformation here! Plants DO NOT use visible light. They use the photosynthetic spectrum, specifically two peaks, one at 440mn(blue) and 650nm(red). The main part of the visible spectrum, green, yellow, and orange are not used by plants, that’s why they look green, plants reflect green light. I’ve been completely unable to find the light transmission rates of low e glass for the photosynthetic spectrum, no one seems to publish this information.

Plants DO use visible light since the visible light spectrum is from 380-780nm and both 440nm and 650nm are definitely within that spectrum.

Visible light transmission graph specific to Cardinal LoE coatings.

Thank you. It’s the first piece of useful, specific information I’ve seen. Most sites just say visible spectrum with no specifics and 75% of the visible spectrum is not used by plants. I keep saltwater aquariums and this information is vital for reef keeping but I was completely unable to find this for the greenhouse I’m building. Thanks!

you're welcome, I am glad that you can use it!

Low e will certainly effect plant growth.

Ultraviolet Light (UV)

Ultraviolet light is comprised of three different wavelength ranges of light. UVC (200-280nm) has the shortest wavelength and most energy, but is potentially the most stressful to plants and human skin causing sunburn and can be very damaging to human eyes. Fortunately, for humans and plants atmospheric absorption eliminates the majority of UVC shortwave light. no need for a window film to block it.

UVB (280-315nm) has a short wavelength, high energy and also causes sunburn in humans and plants. UVB is known to damage protein and nucleic acids in plant cells, causing decreased metabolism and decreased number of flowers. UVB can have positive effects as well.. A plant responds to the stress and sunburn from UVB wavelengths, by creating it’s own sunscreen in the form of trichomes and cretinoid.

Exposure to UVB radiation is also known to reduce a plants biomass, plant height and leaf area, but increase leaf thickness. lack of UVB causes leggy plants.

Finally, UVA and near ultraviolet light (315-400nm) has the longest wavelengths of UV light and can be very beneficial to plant development. Wavelengths in the UVA spectral range are included in the absorption spectrum, particularly in the 380nm range. The absorption spectrum is the range of wavelengths of light that are absorbed by green chlorophyll for photosynthesis. Additionally, research has shown that exposing plants to UVA light can also inhibit mold growth and fungal development.

Far-Red and Infrared Light

On the far end of the spectrum (>700nm) you find far-red and infrared wavelengths of light. Far-red and infrared light have very long wavelengths, and very little energy. Infrared wavelengths are not visible to the human eye and only can be felt as heat. We know that blue and red light is optimal for plant development, but research conducted in 1957 has shown that combining blue light and red light with far-red/infrared light (700-760nm), led to an increased rate of photosynthesis due to the Emerson effect. The protein Phytochrome is the only known receptor that is sensitive to far-red/infrared wavelengths. Plants use Phytrochrome to regulate when a plant is to switch from vegetation state to flowering, and the time of flowering, due to the length of daylight or exposure to artificial light.

The appropriate amounts of far-red and infrared light can also be a very effective at promoting robust stem growth, proper node spacing, and more flowers and fruit. Too much IR radiation can also be an issue because to a plant the majority of IR radiation is felt as heat.

consider the amount of light (PAR or PPFD) needed to successfully grow your plants. then decide if low e is sufficient for you. It may lack certain lighting requirements.

Awesome copy / paste, but what do you think all that information, in relation to using specific LowE coatings, applies when limiting various portions of light spectrum?