photo by Nancy Cordua
IN GARDENING IT HAS ALWAYS BEEN a given:
You dig round holes with round pointed shovels to plant the round rootballs
of landscape trees and shrubs. Not anymore, according to Bruce Asakawa, who is a landscape architect and host of "West
Coast Garden Line," a syndicated radio talk show that's aired locally.
At a Saturday morning lecture in September at Miller Farms Nursery in McKinleyville, Asakawa, visiting from San Diego, gave a presentation centered around the basic principles of plant growth, illustrated by a 5-gallon ficus tree. He revealed to more than 75 eager gardeners the recent changes in planting and transplanting techniques. For example, gardeners should now dig square holes, instead of round ones, when transplanting trees and shrubs, he said. A plant installed in this manner will knit in the soil faster.
"Develop a recto-linear planting pit, rather than a circular one," he advised. "If you think about it a bit, a plant that has been growing in a container for an extended period of time becomes root-bound because the root system grows out from the root flare and fits the inside of the round container and starts to bind itself. So if the root ball is in a round planting pit, it actually delays the penetration of the soil it eventually has to grow in.
"If it were in a recto-linear pit 11/2 times the depth of the root ball and six to eight times the width, the root system will go into the inside of the planting pit and move to the corners and then start to penetrate the soil it has to grow in. So that makes a lot of sense from the standpoint of cultural adaptation," he said.
What this means is that when planting a typical tree in a 5-gallon container the square hole should be about 2 feet deep and 6 to 8 feet wide. That's a lot of digging. In addition, Asakawa suggests the backfill soil be amended with organic matter so that it has a loamy consistency like the soil the root mass was growing in.
Mix the backfill with mulch and compost to give it about 20 to 30 percent of organic matter by volume, he said.
There are also new rules when pruning after transplanting an established shrub or tree, according to Asakawa. It has always been believed that since a good deal of the root mass of a plant was severed after transplanting, the canopy had to be pruned back to make up for the loss, making the foliage in proportion to the remaining root system. Not anymore, said Asakawa.
"It has been found that this (severe pruning) is a negative way of transplanting the plant. Keep in mind that there are auxins in the tip structure in the canopy of the plant which are called plant growth hormones. And in the root system there are plant growth hormones called cytokinins. Cytokinins and auxins are always in proportion in a plant and when the root system is destroyed the auxins kick in and they actually stimulate new plant growth root systems in the newly disturbed plant," he explained.
Cutting back the tips of the branches, said Asakawa, essentially removes the plant's ability to manufacture hormones. "If you were to cut back a plant substantially removing the auxins, you slow down the regeneration of the root system," he said. "So what you can do is defoliate the plant, taking 60 to 80 percent of the foliage, but still leave the tip structures intact."
In a question-and-answer session, Asakawa addressed burnt leaves, nagging weeds, poor soils and pruning overgrown plants. One gardener, plagued with an overabundance of Himalayan blackberries, asked how to get rid of the stubborn intruder. "Move to another neighborhood," said Asakawa, revealing his humorous side.
"The West Coast Garden Line" airs Sunday from 8 to 10 a.m. on KINS 980 AM. Questions can be called in to 1-800-660-GROW.
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