Cold protection of tropical container plants

Q: I am long time customer of yours, I live in San Diego California and while the summer and Fall temperatures are warm to mild, the winter temperatures dip to a point where some tropicals die off. We are experimenting with different variations of way to heat and insulate the pots we have the tropicals planted in as a way to keep them alive during the colder winter months. I was wondering if you knew of the ideal soil temperature for these tropical in order to look their best year round. All of the heaters we have installed have thermostats and temperature adjustments so we can now keep the soil anywhere between a range of between 65-75 degrees. Any advise you can provide would be greatly appreciated.

A: This is a very interesting concept you are working with. Indeed, keeping pots/roots warm, may help a lot! We've been experimenting with cold protection for a long time - for the above-ground plant parts. For sure keeping roots protected (even with a thick layer of mulch) will benefit tropical plants during winter. In case with container plants, this may help dramatically.
The guideline is, tropical plants slow down or stop their metabolism at 65F. As long as you can keep soil above that temperature - this should work great. Of course, the higher the better.
Optimum temperature for growing tropical plants in general - 70-85F. Above 90F, metabolism stops too, unless it's a heat tolerant, desert plant.

Greenhouse in Virginia
Plumeria cold protection
Ghost Cold Protection
Seven rules of cold protection for tropicals
About Cold Protection
Cold protection - winter action for your plant collection
Tropical Treasures articles on zone pushing.

Q: Has anyone ever tried using heat packs under frost blankets to protect tropical plants from frost?

A: The reality is, the heat packs used for shipping do not have enough heat capacity to create efficient warming effect. From our own experience, the best way is to use small 25W incandescent bulbs which produce lots of heat (considering observing all safety precautions and fire safety). Some gardeners use Christmas lights. See picture of our plants in the ground during a cold night. We called them Ghost Cold Protection! ;)

See more columns on cold protection:
Seven rules of cold protection for tropicals
About Cold Protection
Cold protection - winter action for your plant collection
Tropical Treasures articles

Seven rules of cold protection for tropicals

Q: I was always wondering how you guys manage to grow true tropical trees in Florida? I live in Puerto Rico and we have Breadfruit trees growing here in a wild... but my sister lives not far away from you, in Orlando, which is much colder, and I wonder if I can get her a Breadfruit tree for Christmas?

A: Your sister can grow a Breadfruit tree in Orlando either in a pot (and bring it indoors during cold periods) or in the ground inside a structure (an elclosed conservatory with heating system). See our customer's Greenhouse in Virginia. Cold protection of tropical plants is a lengthy subject and we have many interesting publications about it in our managine Tropical Treasures and on the website. In a nutshell, when growing tropicals outside of tropical climate, you need to follow these 7 rules:
1. Cut watering to a minimum. Cold+wet kills tropical roots.
2. Water thirsty plants before a cold night. Jucy leaves have fewer chances to be cold-zapped.
3. Wind protection is more important than a temperature drop. Plant tropicals close to a house or surrounded by other trees.
4. Duration of a cold period is more critical than the cold itself. If expecting long cold hours, bring up all available protection resources. Christmas lights or propane heaters - as long as there is a heat source, everything helps!
5. Remove plastic covers during the daytime so plants don't get "cooked" in the sun. Fabric covers are better than plastic.
6. Grow ultra-tropicals in containers and bring them inside the garage or even indoors during the cold.
7. Use SUNSHINE plant boosters and feed your plants well during Summer to improve cold hardiness.

Related topics:
About Cold Protection
Cold protection - winter action for your plant collection
Improving cold hardiness before winter: fertilizer and micro-elements
Cold hardy tropical fruit trees