Winter Plant Care Guide for Tropical Fruit Trees and Perennial Plants
Over-Wintering Zone 8 and Below
Bring your plants in when the temperature is predicted to be under 45 degrees. Even though they would be fine all the way down to 33 degrees it’s best to be safe and not risk an incorrect weather prediction.
To avoid excessive foliage dehydration and light deprivation bring the plants back outside when temps are above 45. Even if just for a few hours a day it’s very good for them to get sun and natural air.
If possible when keeping the plants from the cold, put them is a basement or garage somewhere warmer than the outside air but away from artificial and dehydrating home heaters. As long as conditions in these rooms are above 32 degrees the plants will survive and actually be able to stay healthy longer because they will not be exposed to the dry air of the heated house.
Tip: A concrete floor of a basement or garage remains stable and warm thanks to the air temperature in the winter. Placing the pot directly on the concrete floor will provide a little bit additional heat to the soil and plant.
Winter Tropical Plant Care in Zone 8
Some small frost sensitive tropical fruit trees and plants can survive outdoors in zone 8 with enough mulch in the winter. Start with heavy mulching in late fall to protect the roots. For additional protection on nights that temperatures will dip below 32, use loose hay or straw to mound up around as much of the tree as possible. The fluffy hay pile surrounding the tree will work like insulation trapping the ground heat and keeping the immediate area around the tree above 32 degrees.
Hay is economical and wildly available in the fall and is a double win because it will work great as mulch for the tree in spring. We have found that hay is superior to blankets and frost cloth in its insulating ability.
Trapping Ground Heat
While air temperatures may be low, the earth’s surface temperature is warmer and more stable. At night when the air temp drops, the heat accumulated in the earth from daytime sunshine naturally transfers up into the air. The hay insulation acts as a blanket trapping some of the warmth on its way up. While this ground heat is trapped in the immediate area around the tree the result is a warmer micro environment and a tree safe from freezing temperatures.
Because extreme winter low temps in zone 8 will likely dip to 20 degrees use A LOT of hay for freeze protection to be extra Frost protected.
Winter Plant Care and Frost Protection Zone 9 and 10
Similar to Zone 8 instructions but protection is needed less frequently and freezes and frosts are less severe and much shorter in Zone 9 and 10. Most years in these zones gardeners enjoy frost-free winters with the occasional freeze every 3-6 years. In Zone 9 and 10, hay is used as an insulator for freeze protection on frost nights until the tree is about 6 years old or large enough to create its own heat insulating canopy. Once a tree has a large/dense enough leaf canopy and thick enough trunk it can be trusted to be strong enough to protect itself from a hard freeze.
Though it may suffer some leaf and branch damage the canopy will protect the majority of the tree and should bounce back with explosive growth in spring. Even large established tropical trees in Zone 9 will greatly benefit from a heavy mulch in the winter.
In addition to hay and mulch as insulation to protect from frost and freeze damage, well-hydrated and healthy strong fertilized trees have better resilience to below freezing temps.
Soaking the ground around the trees in the late afternoon before a freeze or frost will also provide a warmer environment in the trees microclimate. The moist soil around the tree will allow the ground heat to diffuse slowly, steadily helping to conserve the ground heat throughout the night. Keep in mind that on a freezing night, the most damage occurs just before sunrise. This is because by 6 am the environment has been without sun (heat source) for many hours and a majority of the ground heat has radiated away to the cooler atmosphere. Having the soil moist slows this process and conserves the precious little bit of surface ground heat as long as possible.