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Know Your Soil Before Amending


QUESTION: You talk about amending the soil for planting, but when I went to the Theodore Payne Foundation to purchase native plants, they told me not to amend the soil. Should I do it anyway?

--S.B., West Los Angeles

ANSWER: It would be nice if the question on amending the soil was as simple as do or don't. It has a lot to do with what kind of soil you garden in, but recent research would suggest not amending the soil for many natives, as well as for most trees and shrubs that eventually grow large.

When I suggest amending the soil, it is usually for flower and vegetable beds and those other intensively cultivated parts of the garden.

What you want to avoid in all cases is amending only the soil in the planting hole. This creates an artificial, often impenetrable "interface" between native soil and amended soil. It is like putting the new plant in a bathtub, or a container with no drainage holes, which the first rain or irrigation will fill with water. Many common garden plants will survive this; natives tend not to.

Roots will want to circle around in that amended soil inside the hole, as they do in a container, and in the case of trees and big shrubs, you simply can't amend a large enough volume to do any lasting good. Simply refill most of the hole with crumbled native soil, amending only the top few inches so water enters the soil more easily.

What you can do--and you may have to in some cases--is amend the soil over the whole area, say, to a depth of 4 to 8 inches. This will be necessary with heavy clay soils (where native plants, other than grasses, never grew) and on graded lots and hillsides with mineral soils and where no topsoil remains.

Those gardening on reasonably good garden soil may not even have to do this. When in doubt, a soil-testing laboratory can suggest specific ways to improve your soil. You can also cover the ground to a depth of several inches with a degradable organic mulch, such as leaves, partially done compost or wood chips from a tree trimmer, keeping this mulch away from the very base of the plants. These will decay and slowly improve the soil, so they should be renewed from time to time. Bark, gravel and lawn clippings won't work as a soil-building mulch.

It may be too general a rule, but don't amend the soil for natives or for trees and shrubs on typical urban and suburban lots; just amend those beds where you will be digging and planting frequently.

A Little TLC Coaxes Orchids to Bloom

Q: I received a Phalaenopsis plant recently as a gift and don't have the vaguest idea how to care for it. Could you give me as much information as possible so I can take care of this beautiful, exotic plant?

--E.M., Canoga Park

A: The trick to growing any flowering plant indoors is getting it to bloom. But give Phalaenopsis (moth orchids) a little care, and they may bloom several times each year, according to Julie Norman, the orchid curator at the Arboretum of Los Angeles County.

Find a place where it will get good light but no sun in the afternoon. Morning sun is good; so is tree-filtered light coming through a window. Keep it in the bathroom or kitchen, which are the most humid rooms in the house, or set it on a "humidity tray," a wide dish or tray filled with pebbles and water. Make sure the water does not touch the pot or it may rot the roots.

The orchid can probably live in its pot for several years; they do fine when they're a bit rootbound. When you do have to repot, increase the size by only a couple of inches, say, from a 4-inch to a 6-inch container. Use a bark and perlite orchid potting mix sold at nurseries. Don't crowd orchids together; they need good air circulation.

Fertilize every two weeks with an orchid fertilizer (also at nurseries), following label directions. Water about once a week in winter, twice a week in summer or whatever it takes to keep the soil evenly moist at all times. Water in the morning so foliage dries quickly and doesn't develop fungus or keep water off the foliage.

The first flower spike will appear some time in spring, and when it is finished, you can get it to bloom again by snapping off the stalk just above where the third or fourth flower appeared. This will cause the stalk to fork and flower again. After the fork flowers, cut the stalk off at the base so it can't bloom yet another time, which will "cause the plant to bloom itself to death," said Norman.

However, there's a good chance it will produce more stalks, at other locations on the plant, and bloom again in summer or fall.

Cymbidium Shows Its True Colors

Q: I have a wooden planter with seven cymbidium orchids next to each other. When I planted these, they were several different colors--yellow, green, pink, burgundy and white. When they came into bloom the following season, they were all pure white. They are very beautiful, but I would like to know why they changed color.

--C.M., Santa Maria

A: They could not have changed color. It's absolutely impossible, according to John Ernest at cymbidium grower Gallup & Stribling Orchids in Santa Barbara. Flowers can't suddenly and radically change color. They might be more intense or faded looking depending on how much light they are getting, but "we grow hundreds of thousands (26 acres of greenhouses) and they always look basically the same. A burgundy orchid can't change into a white," he said. The plants were either mislabeled or somebody swiped yours and substituted whites for the colorful kinds.

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