I recently received photos of some redwood trees in Riverside that looked like they were struck by lightning. Foliage at the top of the trees was gone and what remained further down was ragged. The reader wanted to know what could be done to save these trees.
I was rather astonished that the trees had done so well in the first place since they appeared to be 20 to 30 feet tall. I had previously thought that a location as far inland and as hot and dry as Riverside would be rather inhospitable to redwoods. Still, if they managed to grow to such a height perhaps they could be revived.
I assume these trees are suffering from the scorching heat and drought of recent years. My first thought was to water the trees with a root irrigator. This device is a perforated metal rod with a pointed tip that is plunged into the ground. You attach a hose to the top of the rod and water flows down and out through the perforations. You move the irrigator around the tree, soaking each area as you go, so that the entire root zone is saturated. The drip line or canopy perimeter line of the tree is where you want to irrigate because that’s where the feeder roots that take up water and minerals are most actively growing. Root irrigators vary from 24 to 48 inches in length. Although nearly all the water a tree requires is absorbed in roots growing only a few inches beneath the soil surface, having a reserve of water below will benefit these shallow roots as it moves upwards in the soil through capillary action.
I noticed that grass was growing up to the trunks of the trees. Grass will compete with tree roots for water and it is advisable to remove grass around these trees (and any other trees, for that matter) at least as far as the drip line. In the case of warm-season grasses (Bermuda, St. Augustine, Kikuyu) with rhizomatous roots that grow horizontally as well as vertically, keeping grass several feet beyond the drip line is essential to allow tree roots to grow without competition.
I expressed my hope to the redwood caretaker that a string trimmer or weed eater/wacker was not being used to trim the grass around the tree trunks. Those who use this power tool carelessly will allow its whirring plastic string to slice into the bark at the base of the trunk, cutting into the xylem vessels through which water moves up the tree. Only where xylem vessels remain intact will the water continue its ascent and the foliage farthest up the tree at its tip will be the first to wither due to this decrease in water supply.
Finally, I mentioned that watering with SUPERthrive could be beneficial. SUPERthrive contains naphthalene acetic acid (NAA), a naturally occurring hormone that stimulates root growth. The application rate is easy to remember: one drop of SUPERthrive per gallon of water. SUPERthrive is available at nurseries everywhere, easily recognizable by its small brown plastic container with a label touting its many beneficial properties.
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I received the following email from someone who gardens in containers: “The plants and soil in my tall (28″ to 36″) pots keep sinking. What can I do to prevent this?”
The answer to this question depends on the age of the soil. If the soil was fresh and recently placed in the pots (followed by the plants), it’s probably the result of the soil lacking wetness prior to its placement. Soil that is not saturated prior to filling a pot will compact when it is watered. That’s why it is essential to saturate your soil mix before putting it in pots.
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The more likely scenario, however, is that the soil mix included compost or other organic constituents that have decomposed over time, resulting in the sinkage described. Compost in container soil mixes usually decomposes within a year while peat moss may take several years to break down. Coconut fiber or coir is recommended as a substitute for peat moss since it provides the same water-retaining function but decomposes more slowly. Finally, if the soil mix included perlite some of that material may have also been lost over time. Perlite is light and rises to the top of containers where it can be blown away. Pumice is a recommended substitute for perlite since it also enhances drainage in the soil mix but is heavier and stays put. A bonus of pumice is that, unlike perlite, it contains minerals that enhance plant growth.
California native of the week
Banana yucca (Yucca baccata) is native to the high desert and can survive winter cold down to 20 degrees below zero. It is a stunning clumping plant with blue-green leaves and stout clusters of creamy white flowers that are both fragrant and edible. The prized fruit are shaped like purplish-green bananas and may be consumed raw or cooked. Upon being baked or roasted, their taste and texture resembles that of sweet potatoes. The fruit pulp may also be dried and stored in that condition or made into cakes. The only nursery I found in Southern California that grows and sells banana yuccas is Serra Gardens in Fallbrook. However, T-Y Nursery, a wholesale grower of banana yuccas, supplies Green Spot Nursery in Sun Valley, Vineland Nursery in North Hollywood and Sakioka Nursery in Westminster so you could special order the plant from any of them. Banana yuccas are also available by mail for $15-20 through online vendors you will find when searching “Yucca baccata” on both amazon.com and eBay.com.
Send questions, comments, and photos to joshua@perfectplants.com