Depending on where you live, there are steps you can take to protect the heat-loving subtropicals from their mortal enemy, cold weather. Take for instance this jackfruit (figure A) growing on a hilltop in San Diego (figure B). If the temperature dips below freezing, it's a goner, so the plant's location is critical to its survival. Spellman planted this tree on the edge of a slope where the cold air falls away. It's also planted close to the wall of the house where it receives reflected heat from the surface of the house. Spellman took further precautions by planting it in a soil that has been thoroughly amended and mulched so that it is very fast-draining. He also uses an easy-to-make, customized plant cover (figure C). To build your own protective plant cover, drive four wooden posts into the ground just outside of the foliage line to provide a structure for the cover. Cut and staple a lightweight row covering to the posts, being careful not to pull too tightly because the tree needs air circulation. Then add another length of material crosswise to enclose the tree. This cover provides up to five degrees of additional frost protection. "It's not the saving grace if we have a really severe frost," says Spellman, "but for temperatures down to the mid to high 20s, you're going to get good results from it." The tree cover should stay on until the threat of frost has passed.
For colder climates where a cover is not enough protection, there are more elaborate options. Some gardeners use plastic coverings with small space heaters or light bulbs to keep up the temperature. "Extreme beauty sometimes calls for extreme measures," says James. Another way to nurture subtropical plants is something you probably do already for the rest of the garden--mulch. Wilson recommends using mulch because it holds in moisture and increases the bioactivity in the soil. By encouraging earthworms and beneficial fungi to live in the soil, it also allows the plants' root systems to take up nutrients in a much more efficient form.
If you're still not sure about providing adequate frost protection outdoors, make it easier on yourself and grow your subtropical plants indoors. "Most varieties in areas east of here are only going to be outdoors for the summer," says Wilson. "You're going to have to put them in a glass house or enclose them in a screen porch." Subtropical plants need to be grown some place where they can be maintained in a frost-free environment.
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