Invasive roots
Q. How can we prevent roots from shrubs from invading our sick looking fruit trees?
A. Invasive roots are a serious problem in California, especially in old gardens. The best solution is to install a root barrier. The method is to dig a two or three-foot deep ditch and install a commercial root barrier vertically inside the ditch and then replace the soil. Root barriers are made of several materials including rubber, plastic, stainless steel, and fiber glass. Most tree and shrub roots are mainly located in the upper levels of the soil, so depending on the species of shrub that is sapping the strength of your trees, you may not need to dig a very deep trench in order to give your trees the necessary protection.
If you do a search on the internet for “Tree Root Barriers” several manufacturers will come up, including Deep Root and Century Root Barrier. Root barriers are widely used to contain the roots of running bamboo species and also to protect sidewalks in urban environments.
You will also need to fertilize and mulch your fruit trees in spring in order to get them growing again. If they are, as you said, “sick looking” most likely they’re starved for adequate nutrition. In warm-winter climates deciduous fruit trees may be fed lightly in spring just as flower buds swell. Citrus trees are heavier eaters. A mature citrus tree can take up to 1 pound pure nitrogen per year beginning in late January. Consult my book Pat Welsh’s Southern California Organic Gardening, Month by Month for specific fertilizing requirements and exact directions for fertilizing fruit trees, including avocados, citrus, deciduous fruit trees, and bananas along with many other plants and detailed explanations of organic methods and applications.
Trying to remember name ofsmall invasive plant –with red and yellow leaves–but with roots 18 inches long. Will invade lawns, gardens, etc.
Can be grown in pots only. Roundup the only thing which will kill it.
Dear Enid:
Do you mean oxalis? (There are both yellow and red-leaves varieties of this plant.) Or do you mean knotweed (Persicaria capitata, Polygonum capitata)? It is a deep-rooted ground cover with red and green leaves and pink flowers. Some varieties of Persicaria have more colorful leaves.
Many thousands of plants are grown in Southern California gardens, and an invasive plant having “red and yellow leaves with roots about 18 inches long” is not enough information for plant identification.
But one thing is clear, don’t use Roundup! Whatever the problem, just pull it out or kill it with soil solarization (described on pp. 295-296 of my book). Follow up with an organic non-poisonous pre-emergent herbicide, such as corn gluten meal, to prevent its return from seeds. Roundup is a poisonous chemical product that has been shown to be more dangerous and more lasting than previously supposed. It lasts in the environment and can invade groundwater.