Would a large cold frame be warm enough to grow citrus here?

11 years ago

Hello,

We are about half-way North-South in Tennessee. Some maps put us squarely in zone 6, and others in zone 7.

We'd love to try our hand at some citrus, including 'cold-hardy' varieties of lemons, limes, oranges (if possible?), as well as things like Avocados.

We did a regular vegetable garden ~2,000 sq.ft. last year but are still definitely newbies.

We're looking at potentially purchasing a cold frame about 15x30 and 8' high - but not sure how warm it would really stay in the winter without adding heat. Thoughts? Is there hope for citrus here?

Thank you!

Comments (4)

AmericanGardner
Original Author
11 years ago
I should add, so far we are thinking we'd cut food-grade 55-gallon barrels in half to put each tree in a 27 gallon container, under the cold frame.

We'll also probably utilize the shorter sides of the cold frame to grow seedligs in spring, and greens through parts of the winter.

Thanks!
mksmth zone 7a Tulsa Oklahoma
11 years ago
Whatever it takes to keep them from freezing is in a nut shell all you need to do. I grow mine in containers in my greenhouse during winter.

Mike
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It might help to read Eliot Coleman's books on season extending techniques. I have a high tunnel (plastic covered/wood frame) and it is amazing how warm it gets during the day when the sun is out. What I have learned is the soil inside doesn't freeze even though outside it might be zero degrees and it gets zero degrees inside at night. From the list that another poster provided, those are cold hardy plants that can take some cold temperature extremes. Local farmers start using supplemental heat when they want an early tomato crop but they don't try to grow tomatoes all year. You also need to understand that during the darkest winter days, plants aren't getting enough sunlight so they tend to stop growing. Eliot calls this the Persephone Period. Depending on what you are trying to grow you might need both heat and light. (New local hydroponic greenhouses are using a lot of light.) Local market gardeners provide extra cold protection for their plants by using Agribon. I managed to keep rosemary alive for two winters here in zone 5 NH by swaddling the plant with Agribon, removing it in the spring. By providing enough cold protection you can probably grow spinach in the winter but not lettuce. I have had lettuce roots survive and start growing in the spring. Kale, coriander, and claytonia might die but seed and/or roots survive to start growing in the spring. Keep in mind that even snow provides some insulation. Johnny's Seeds website might also have some helpful information about when to sow plants for fall/winter and when to sow in the spring for earliest crops.
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I did get a scion off his Changsha tree. He grew five Changsha plants from seed, left the small seedlings outside one winter, only one of them survived. He later grafted that Changsha plant onto a rootstock (he can't remember which, probably either poncirus or citrange) and eventually planted it in the ground outside, up against his house. He covered the tree for the first two years, giving it a chance to grow without suffering too much cold damage. But I made sure to specifically ask and he told me he had not bothered to cover the tree the last time (it was not a mild winter that year). The tree you see in the picture is that tree. He believes this seedling of Changsha that he selected might be slightly hardier than regular Changsha. But he is not really sure, and there's no real way to know at this point. Just in case anyone was wondering, this is zone 8. I don't think any of these trees would make it in zone 7 this far so north, with the exception of course of Poncirus trifoliata, and possibly citrumelo in zone 7b. So if you live in a colder climate zone designation, this is likely not going to be possible for you. Trying to grow these here in zone 8 in this cool climate region is already pushing things.
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trianglejohn
11 years ago
I have a 20 by 30 hoophouse in zone 7b (Raleigh, NC) and my citrus do fine most of the time. I have two small electric heaters running most nights and when it calls for below freezing temps I use a wood burning stove. The wood stove can really crank out some heat but you have to baby it all night long - hopefully I will get better at it over time.

Some of the citrus decided to suffer this year (even though it has been mild so far) so I have rigged up a tent inside the hoophouse, a sort of greenhouse inside a greenhouse. I put one of the electric heaters in it and run it all the time - so far it seems to be helping.

You could partition off sections of your structure so that one section is super heated while others are not and keep the really delicate stuff in that section.

Heating the hoophouse is not the problem. Keeping the heat inside is the big problem. Plastic sheeting just doesn't hold on to heat very well.

You can allow things to cool down to the point where your plants go dormant and then you can lower the light levels by covering the structure with a pool cover or other sort of thermal covering. You can eventually get the covering built up to the point that the whole thing keeps itself warm - but you won't have much light which the plants need to stay active. But by encouraging them to go dormant (dry, cool and dark) you won't have to do much work and often they survive til things warm up in the spring. All of this falls apart if you want to grow crops at the same time. If you increase the light levels enough to encourage growth then you have to keep the space much warmer.

I have all sorts of citrus and they do not always follow the rules - some that are supposed to be delicate have no problem with winter cold while some that are supposed to winter hardy almost die each year. Some do fine for years and then all of a sudden go downhill, so you have to be flexible.

It can be done, but it does require a bit of planning and work. If it was easy, everyone would have citrus in their gardens.
jacklord
11 years ago
It would work so long as you provide adequate heat and properly vent it so that, paradoxically, it does not overheat on sunny days.

Strings of 100w or C9 Christmas lights would probably do the trick. I have also seen where people use small ceramic heaters or aquarium heaters in buckets of water.

Would a large cold frame be warm enough to grow citrus here?

Comments (4)

AmericanGardner
Original Author

mksmth zone 7a Tulsa Oklahoma

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Would a large cold frame be warm enough to grow citrus here?

Comments (4)

AmericanGardnerOriginal Author

mksmth zone 7a Tulsa Oklahoma

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trianglejohn

jacklord

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AmericanGardner
Original Author