Cold Protection

Q. How do I protect my trees from cold weather?

A. The Treasure Coast is in the sub-tropics, which means weather is usually mild, but we can get cold or freezing temperatures a few days each year; now and then we get tree killing cold snaps. How your fruit trees react depends on the species. If you grow true tropical trees, you will need to take extraordinary measures to protect them. For Durian, Mangosteen or Breadfruit you would need a heated greenhouse and a lot of luck. In northern Treasure Coast, Abiu, Soursop and Mamey Sapote are especially difficult to keep alive. Cashew trees are extra cold sensitive (the 50s can kill them) when very young, {a little less so after a few years;  they will fruit in a container, so grow them that way so you can bring them in when necessary.}
The “TC Fruit List” page indicates trees that need special cold care.

The most cold sensitive tree set out in my yard (Vero South) is probably the Black Sapote. When the temperatures got down to 26° two nights in a row a few years ago, it lost all its leaves and branches. Since I wrapped the trunk with the old-style incandescent Christmas lights and covered the tree with frost cloth, it survived and was covered with new growth by summer. It bore less than a dozen fruit the next year, but has done well since. I’ve seen full size Black Sapote trees in Ft. Pierce, typically the northern limit.

• Cloud cover is good; clear skies increase radiant cooling.
• A light wind keeps frost from settling. Strong wind is not so good, and no breeze at all is not good.
• Sudden cold snaps are more damaging than when plants are able to more slowly adjust to cold.
• Cold air settles. Florida is flat, but slight differences can still channel cold air to low spots. Be aware of micro climates before planting your trees.
• More protection is found next to a canal, river or lake, anywhere on a barrier island with water on both sides or with container plants in a screened pool area.
• Your house can provide shelter, as can trees. The south edge of a taller tree can still get sun but be protected from radiant heat loss. You could espalier trees on the side of your house, especially on the south face, but take care: some trees behave well near structures, others have invasive roots or are difficult to keep small.

• Grow more cold tolerant fruits like blueberry, figs, jaboticaba, jujube, pomegranate, white sapote. Some avocado varieties like Brogdon, Day, Florida Haas, Joey, and Winter Mexican can take a lot of cold. Choquette, Hall, Lula, Marcus Pumpkin and Monroe are medium cold hardy, and should do fine in eastern IRC and southern TC.
• Water the ground a few days before the cold weather hits. Water holds a lot of heat from the sun, which can radiate and create a micro-climate around the tree.
• You may have heard commercial orchards sometimes spray water to cover the branches with ice, which keeps them from getting colder than 32°. Don’t try it at home: it only works under certain conditions. Especially with wind, this can make things worse.
• Some foliar micro nutrients can give the tree enough of a boost in strength to withstand a few degrees lower temperature than they otherwise would. Spray on the leaves in the fall. Also keep your trees on a regular feeding schedule to keep them in top notch health. Stop fertilizing in September to encourage winter dormancy. Don’t start again until around mid March, depending on the forecast.
• Cover trees with frost cloth, burlap, sheets, or blankets. This can protect from radiant heat loss and wind chill, and can trap any heat from the ground or heating devices. Be aware if the cloth touches leaves, those leaves may freeze and die, especially in cold wet weather.
* Don’t use plastic unless you remove it first thing the next day. Otherwise the trees will cook when the sun comes out. Leaves touching plastic will freeze worse than on cloth.
• Watch for dessication on a sunny day after a cold night. Provide water the next days to keep the tree hydrated.
• Combine a cover with incandescent Christmas lights. (Don’t wrap the lights, loop them around the trunk and clip the lights to the wire. It is much easier to remove them that way.) The idea is to protect the trunk and main branches from freezing, not the whole tree. (You can get lights right after the holiday for big discounts, but who knows how long they will be made. LEDs are the new thing, but they provide no heat.) Alternatively you could use a regular incandescent lamp, but only if there is no chance of rain, or use an exterior grade fixture. Be careful with extension cords, especially if there might be rain. Follow all label precautions to prevent a fire or shock.
• Be sure to also protect the graft area. Wrap the trunk with insulating material, or mound up leaves. Be sure to remove them as soon as the freeze threat is past.
• If the outer branches freeze and die, do not remove them until mid March, even if it is ugly. Pruning will encourage new growth which will die if there is another cold snap. Also the dead leaves will protect the living branches below.
• Don’t assume a tree is dead–give it time to re-sprout. As long as it sprouts above the graft, the tree can recover. Remove any sprouts below the graft. If that is all you get, the named variety is lost.
• Group your most sensitive trees together and use a patio heater in the middle.
• Grow your most sensitive trees in containers. Move them in the garage or inside, or tip them on their side and cover with blankets.
• Add a tall post next to sensitive trees. Then use the post to support frost cloth protection, to keep it away from the leaves. Or build a frame around a tree to stretch a temporary greenhouse around.
• Build a greenhouse. (Or a portable garage from Harbor Freight is often on sale {$180 in Feb ’15} minus one of their 25% off coupons.)