As soon as the heat wave abated, I received an email from Gerda Maxey, an avid 92 year old gardener in Sylmar. Maxey was thrilled because her flamboyant tree (Delonix regia) was flowering like never before. Germinated from a seed she brought to Sylmar from her native Paraguay, the parkway flamboyant is a rebuke to everything you thought you knew about tropical plants. According to Sunset Western Garden book, this tree can only grow locally in Santa Monica or Malibu, yet I have never seen it in either place. Astonishingly enough, it thrives in Sylmar, far removed from the beneficent coastal influence that it supposedly demands in Southern California. You would think that such a tropical species, native to Madagascar, would have been seriously burnt by the recent heat, if not by the Valley’s winter cold, yet it has come through unblemished. Perhaps the seed that Maxey brought from Paraguay carried within it resistance to temperature extremes that was previously absent in this species.
During the recent heat wave, something curious happened. A tree that had every reason to burn or at least get mildly singed emerged unscathed.
But first let’s mention some horticultural favorites that did suffer heat damage, such as Nick Kurek’s ‘Little Gem’ magnolia tree in Granada Hills, Ronald Chong’s pitaya cactus (bearer of dragon fruit) in Hacienda Heights, and just about everyone’s tomatoes.
A quick habitat check explains why certain plants burned while others did not. Magnolias are native to the humid Southeastern USA and pitaya cactus comes from steamy Central America. Tomatoes trace their origin to the tropical highlands of Peru and Ecuador where the weather is balmy and much like spring throughout the year. In other words, plants that burnt in the recent heat wave were not meant for such harsh summer temperatures.
The leathery, waterproof cuticle that covers magnolia leaves as well as the succulent, water tight stems of pitaya cactus — meant to serve as barriers to water loss — were no defense against sizzling temperatures. When water exits a plant’s leaves faster than it can be replenished by water taken up by the roots, burning may occur.
So what do you do about a tree or other plant with foliage that burnt from the heat? The same thing you do when foliage burns in the winter from freezing cold. That is, you do absolutely nothing. As long as there is some green foliage or even if only parts of some leaves are green, your plant should eventually make a complete recovery. It is not a good idea to detach dead leaves from a burnt plant because those leaves may be shading healthy foliage that could also burn when suddenly exposed to all day sun.
The one thing you don’t want to do is over water a plant when it has lots of burnt foliage. Burnt foliage means that the quantity of foliage for taking up water from the roots has been reduced. If you water excessively, you are likely to end up with water standing in the root zone, which is a formula for development of root rot, typically brought on by dormant fungal spores that come to life in the presence of warm, water-logged soil.
Getting back to the tree that should have burned, but didn’t . . .
Tip of the Week: Another strategy to shield your plants from heat damage is to place garden or landscape fabric over them. This material is sometimes referred to as “floating row cover” because its primary function is to shield rows of vegetable crops from cold and windy weather, yet it is also prevents overheating and sunscald, allowing in only 70% of the sun’s rays. Row cover fabric, readily available online, can be placed directly over your tomato plants, for example, or you can float it over them through the use of wire hoops or supports made of wood or PVC pipe.