Cold-Hardy Citrus Varieties for the Georgia Gardener
Citrus, in Georgia? Surely you jest...
Commercial cultivation of citrus in America tends to center around three major growing regions: Florida, California, and Texas.
For many years, citrus cultivation was all over the south, with large orchards in Alabama, Louisiana and even Georgia. A few hard freezes wiped out much of the commercial orchards, and improved production from other places, with innovations in storage and shipping, meant only home gardeners really bother with citrus production, on a very small scale, elsewhere than the farthest southern fields. Still, on a small scale, without the wind turbines blasting hot air or the gas furnaces burning among the hedge rows, home gardeners can grow a tree or two with some planning in advance and preparation for the freezes that could, once again, sweep down from the north and slaughter subtropicals in a flash.
Citrus Basics for Northern Climates
Growing fabulous oranges, lemons, and limes outside of their normal growing zones is a challenge, but fresh fruit in the doldrums of winter, glistening like christmas ornaments from the long, lush branches of a tropical tree is like a message delivered in wrapping paper from summer sunlight. When I step out to my struggling orange tree, my little lemon tree, and my calomondins and kumquats, there is nothing else blooming and producing, and certainly nothing with the explosion of flavor. I haven't successfully gotten all my little trees to produce every year, and I have had casualties along the way, but in the morning darkness, when the air is so cold and summer is just a distant memory, these lovely packages arrive.
You are denying nature. When you take citrus away from its native climate, you are going to have to take measures to mimic what has been lost.
You will need fertile soil, like a subtropical jungle. This soil must not be Georgia red clay. You need to build up above it. Citrus need drainage. Build up a mound, or raised bed, at the very least, if not just keeping the trees in pots. Cactus soil is ideal. In the ground, water once a week deeply, allowing the soil to drain away completely. In the pots, water when the soil is dry down to an inch or two. In the ground, fertilize twice a month, per the instructions on your package of organic fertilizer. In a pot, a tablespoon of fertilizer mixed into the water will help the plant thrive.
Light, heat, and the sun are all required. Look for white fences, if you have them. I have a white shed, and I planted my long-suffering orange tree there, against it. The extra light generated from the reflection will improve growth. Full sun is best, but citrus can thrive in partial shade, though fruit production will suffer. Shade can be beneficial, in some cases, because a wall of other trees can shield the tender citrus from fronts that blow through. A few precious fruits are better than none at all.
Do not make the mistake I made with my long-suffering orange tree. Figs and oranges both have very shallow roots that compete with each other. Keep them far apart, to keep both their fruit production up.
Citrus don't like mulch, except when they do. Keep the mulch at least a foot away from their roots or risk root-rot. I lost a lovely lime tree because I thought I should mulch the roots in the pot, and this was a mistake that ultimately killed the tree.
In cold snaps, bare ground is actually warmer than mulched ground. But, one technique which I am trying right this moment is to mulch high above the bud graft union, to preserve the main trunk. My results have been mixed.
I have both potted citrus and in-ground citrus, and I can see the benefits and limitations of both methods.
My poor orange tree has suffered so many trials and errors, that it is a testament to the toughness of citrus that it is alive at all!
To Pot or Not to Pot?
There are advantages and disadvantages for growers.
Trees prefer ground. They require less water, less fertilizer. They produce more fruit and more lush foliage. However, they are not acclimatized to cooler climates north of zone 9 (or sometimes 8 for specific varieties like Kumquats and Changsha Tangerines). The trees, regardless of cold-hardiness, need to be dormant to survive winter weather. Most of America have these cold fronts that come sweeping through suddenly, even in Spring. A dormant tree is more cold-hardy than a growing tree. Growing trees can suffer severe damage, even death, when the cold wind blows through suddenly in the spring. Coastal climates tend to succeed over inland ones, with the body of water to regulate the temperature. Inland growers (like me, near Atlanta) can still manage it, but extra precautions are necessery to succeed.
Some trees seem to prefer pots. One of my favorite sour citrus fruits, the Phillipine Lime or Calomondin, thrives under the root-pruning necessery to keep the plant small. It produces abundantly in pots, and the quality of the fruit is very high. The ease of moving the plant in the pot means you can strategically place the blooms where you want them, and savor that amazing, intoxicating aroma anywhere you happen to be. Kaffir limes also seem to do very well in pots, and might not require root pruning much, in a large-enough pot. I have never seen fruit on my little Kaffir, but it is the leaves that we use, regardless, so worrying about fruit production is not a concern.
Pots have serious advantages for northern growers. Being able to move the tree is huge in winter. Controlling the soil and the fertility and the size of the tree takes the guesswork out of growing conditions. But... Fruit production is not as great as if it were in the ground. The extra care necessery to keep the plant thriving can be a hassle to inexperienced or busy growers. Though drought-tolerant, potted citrus require a strict weekly watering schedule, or they will defoliate and eventually die.
Approximate Cold-Hardiness of Different Citrus Varieties, From Various Sources
32 degrees F
32 degrees F
32 degrees F
32 degrees F
30 degrees F
28-32 degrees F, per variety
20-26 degrees F, per variety
18-26 degrees F, per variety
15 degrees F
15-20 degrees F, per variety
Yuzu/Sudachi (Japanese Sour Citrus)
15-20 degrees F, per variety
Small, more shrub-like
10-15 degrees F
8-15 degrees F (Tree is more cold-hardy on its natural roots, not grafted! Grow true from seed for best hardiness!)
Trifoliate Orange (Inedible Ornamental Rootstock)
Overwintering Potted Citrus Indoors
Once the temperature outside reaches about 40 degrees, most citrus varieties are ready to be covered. A little chill won't hurt them. In fact, a steady chill can help a ctirus "go to sleep" and go dormant, improving the lifespan and fruit quality of the tree. Just be sure to watch that thermometer! Once the weather drops down into the low forties at night, it's time to move the precious cargo into a safer location.
First, prepare the plant for its new home by pushing it up against the house, near where it will be going inside. A protected spot on a porch. Ideally, the plant should remain in that location for about a week, but if weather threatens, it's time to pull it indoors, even early.
Once indoors, there are simple tools you will need to place the plant where it can thrive. A south-facing window is ideal. However, strong lights on timers will also succeed in producing enough light to keep your citrus going in a dark room or garage.
Let's go over some of the basic conditions first, and then walk through the steps.
- Temperature - Cooler is better. Subtropical trees like citrus like to overwinter in the 40-50 range.
- Humidity - Jungle trees do not do well in dry conditions.
- Light - Just enough, not too much!
Citrus trees benefit from some cold-dormancy. In climates like Georgia, where a garage will keep some chill, keeping the plant in the garage with a light source is ideal. It will allow the tree to slow down, go dormant, and reduce its water and humidity needs. A cool guest-bedroom is also an excellent choice.
Once inside, most growers are shocked to witness the leaves and blossoms and precious fruit drop off! Humidity is vital to the survival of the plant. Locate an inexpensive humidifier and experiment with your particular citrus and conditions to ensure that just enough moisture is in the air to mimic the subtropical forests of Southeast Asia to prevent leaf-drop. The temperature of the room is related to the amount of humidity you require. The colder the room, the less moisture. In our garage in the Atlanta area, I do not need to add a humidifier. There is enough cold moisture in the air to keep the leaves from falling. If I try to drag them into the house to enjoy the winter blooms, I need to add a humidifier with at least 3 gallons of water to keep the plants going well and green.
A light on an 8-hour timer is ideal to keep the plant in adequate and consistent light over the cool months. (It's much easier than remembering to open the blinds in your distant guest-bedroom every morning, he says, from experience!) The kind of light matters, too. I've found halide lights are fantastic, and had little luck with LED grow lights. You see, the grow lights are expensive, and the trees in question are very large. Large grow lights are even more expensive. A skilled home repairman can install a simple hanging fluorescent light for less than 100 bucks wide enough to cover a small, potted forest. Even unskilled folks can angle a couple floor lamps with halides inside, Even simple fluorescent supplemented with a window should be sufficient to produce adequate light.
Now, before you go rushing to grab citrus and think of casually moving it around, let's talk for a moment about the actual journey from house to winter location...
Citrus can thrive in large pots. These pots are heavy! A 15-gallon ceramic pot full of soil, holding a beautiful tree, is going to need a team of movers and a quality cart to get the plant indoors. Some growers recommend keeping the pot on rollers, but too often I've seen these rollers get damaged by the weight and wetness and mud and rust and all sorts of other things. A damaged wheel can send a whole tree tumbling!
Moving from a patio or yard into a room of the house also means bumps, lifts, and all the little steps and stairs that separate your guest bedroom from the place where the citrus is.
These pots are heavy. Clear a path. Check the path. Figure out how you can best move these heavy, heavy pots into the house. When you think about watering, you will need to adjust the amount of water based on your temperature. Warmer plants, for instance, in a heated house, require more water, light, and humidity. Can the room handle the humidity? Is there exposed wood that may warp or rot? Is there a mat down for any splashing of water, or leaking from the watered pot?
Plan out your day and week with this new chore around the house. As you imagine this chore, remember that it is not so bad the first week, but the second and third it can get bloody inconvenient to pamper your tree in conditions it does not take naturally to having.
Citrus trees can be overwintered inside. Often they are best overwintered inside. Perfume from the intoxicating blossoms will fill the air, and it will be amazing to sit and drink tea and read next to the aromatic blooms in the darkest months of winter.
But, I have found that the less extra work I make for myself, the better. I prefer to overwinter my citrus trees outside.
Winter Protection for Outdoor Growers
Some citrus is small enough that even when winter protection is necessary, the plant thrives with minimal care with only a moderately-sized green house. Certain cold-hardy varieties will thrive with minimal protection and careful planning even as far north as the Carolinas!
- Location, Location, Location
- Variety, Variety, Variety
- Planning, Planning, Planning
Location is the first key to success, and seeking out the best micro-climate for minimal sudden temperature drops, with room and readiness for your winter-protection plan will make a huge difference in plant survival and fruit.Think against stone walls, fences, sheds. Anywhere rigging some greenhouse plastic would be simple and quick to do on a cold winter's night. Also look for locations with access to an electricity source. A plug-in heater or Christmas lights can make a huge difference for your tree's survival on the coldest winter nights.
For marginal climates where lots of winter protection is necessary, smaller is better. Kumquats, Meyer Lemons on dwarfing rootstock, Mexican limes, and smaller satsuma mandarins are ideal. Many of the smaller citrus varieties are even more cold-hardy than the enormous shaddock. They are easier to cover, as well.
For smaller citrus varieties, like Mexican limes, minimal pruning allows a large pop-up greenhouse ample space to cover the whole plant. Kumquats and Calomondins are so cold-hardy, they might not even need coverage most of the time. In zone 8, kumquats, calomondins, and even some tangerines are winter-hardy most winters, and will only need occasional protection from hard freezes and truly low-temperatures.
See the table above for cold-hardiness and size and plan accordingly.
Planning really is the key. Let's go through the steps...
1) You've selected a location that would be easy to protect in the winter.
2) You select a variety that you enjoy - I recommend everbearing acid fruit like the glorious Calomondin or Improved Meyer Lemon on dwarfing rootstock - and would like to grow that is sufficiently dwarfed enough to permit ease of winter protection.
3) You have a pop-up greenhouse, either purchased or constructed, sufficiently sturdy enough to handle your worst winter weather.
4) Plant your tree in spring, as soon as danger of frost is past. Fertilize monthly with citrus fertilizer per package instructions until July. Do not fertilize past July. Mature growth overwinters better.
5) Be ready. Set up weather alerts. Lay everything out.
6) Before the first frost, set up the pop-up greenhouse structure. Place a bucket of water inside the structure to allow water to evaporate, insulating the air itself. For really cold temperatures, old Christmas lights (not LEDs) give off heat and look beautiful wrapped around the trunk and branches. In truly terrible weather, a small heater may even be brought in. I've used everything from odd sized ceramic pots set up with candles inside to create a covered "oven", and even electric heaters.
7) Any frost damage, leave alone until spring. Any pruning action will be a stimulating event spurring growth. Do not prune off deadwood until spring.
8) In the morning, after the freeze, open up the "greenhouse" for circulation. If the weather creeps up above freezing, you can consider removing the greenhouse, but watch out for wind chill.
The real danger for outdoor citrus isn't really winter, but the transitional phases before winter and into spring, when sudden temperature changes come while the tree is still actively growing. A dormant citrus tree is far cold-hardier than one might expect. Certainly, limes will not survive cold temps, but a Changsha tangerine, once fully-dormant, has been witnessed surviving snowfall as far north as zone 7! They don't call it the "ten degree tangerine" for nothing!
General Guidelines for All Growers
Some advice for citrus growers:
Take it easy on the pruning. Citrus can be pruned into a small hedge, but once the desired shape is reached the only reason to prune is to prevent infection and encourage a little light to penetrate lower into the canopy. Cutting out crossing branches is fine, but it is really best to leave the tree alone. When in doubt, don't cut anything out. Pruning will reduce fruiting, and pruning at the wrong time can spur new growth when you don't want to risk low temperatures.
Citrus trees need fertilizer to produce an abundance. A monthly addition of citrus-specific fertilizer is a great idea to keep the tree productive. Organic citrus fertilizer is readily available.