Magnolias not easy to grow in desert

Q: I'm probably going to be at the mercy of the stock at the local nursery . I really liked the 24-gallon magnolia tree they had, but do you think my space of 18 feet by 14 feet will be too small for a magnolia?

A: As long as you understand I am not endorsing planting a magnolia, but if that is what you want, then read the following. Magnolias can get huge, so if you want to enjoy it for a few years and yank it out when it no longer does well, then go for it. You might get 10 or more years before this happens.

Do not put it close to a hot, south- or west-facing wall. But you must plant it in a hole that is 3 or 4 feet wider than the container. Mix good compost (bagged and good stuff will be expensive) half and half with the soil you take from the hole and remove rocks that are baseball sized or larger.

Mix a fertilizer like 16-16-16 with this backfill, about one handful for each 10 gallon bucket. Mix it all together and put this modified soil back into the hole surrounding the root ball of the plant.

As you are putting this soil back into the hole, add water from a hose so it makes it the consistency of quicksand. This helps get rid of air pockets and lets the slurry flow all around the root ball.

Plant the tree at the same level as it was in the container. Immediately after planing, water it deeply, three times, when the soil has drained. After planting, it will be watered best with something that can deliver a lot of water, because this tree will require lots of water each time it is watered.

The amount of water should be equivalent to filling a basin around the tree with 3 inches of water; if it is a 15-gallon plant, then apply 15 gallons of water. You don't have to use a basin, but this basin idea should give you an idea of the amount needed.

If you use drip emitters, then you should initially have at least three emitters for a 15-gallon tree. If it is a 24-inch boxed tree, then you should put at least at four emitters. As the tree gets larger, you will need to add more emitters and more water, perhaps 1 or 2 gallons more at each application per year of growth. Big trees use more water than little trees.

Lastly, dig out an area around the tree that will allow you to put about 4 inches of wood mulch in an area covering a circle, at least 8 feet in diameter, around the tree .

Q: Is deep-root fertilization a good way to fertilize our African sumac tree, purple sage bushes and the purple plum tree? I've seen advertisements from some landscapers for this process.

A: There is nothing special or magical about deep-root fertilization from landscapers or done by yourself. If done properly, and many do not, the fertilizer is injected into the soil at the depth of the roots. This is usually only a few inches beneath the surface of the soil.

Deep-root fertilizer applications have made a name for themselves mostly where trees and large shrubs are growing in a lawn. By applying fertilizer beneath the surface of the lawn, high amounts can be applied without damaging or killing the lawn or causing dark green spots of tall grass where the fertilizer is injected. The amount of fertilizer applied is quite high, so the "saltiness" of the fertilizer (all fertilizers are salts of some sort) would normally kill the grass if applied directly to the lawn.

Also, lawn grasses are fertilizer "hogs." Because of their fibrous root system, they take fertilizer, nitrogen in particular, easily and quickly from the soil, thus robbing it from deeper-rooted trees and shrubs. By placing a complete fertilizer (one containing all three elements: nitrogen, phosphorus and potassium) several inches beneath the soil surface, it places the slower moving phosphorus and potassium right where the roots are feeding.

Commercial companies will usually use a liquid fertilizer and inject it with what is called a "soil needle" or deep-root feeder. This is a probe that is connected to a tank on the back of a truck containing a fertilizer solution. A hose comes from the tank through a pump and, under high pressure, the liquid fertilizer is injected into the soil.

Real fancy units will allow the operator to squeeze a handle on the injector (a probe with holes in it ) and apply a precise amount of fertilizer solution with each injection .

You will know if they are doing it correctly by how deeply they push the injector. If they push it too deeply, the fertilizer will be placed beyond the plant roots and a large amount will be wasted. If they don't push it deep enough and it is in a lawn, then you may have burn spots in the lawn. Burn spots are usually less of a problem in the winter months.

You can deep-root fertilize your own trees and shrubs by using tree and shrub fertilizer stakes and pounding them into the soil a few inches beneath the surface. You also can do it by irrigating the lawn and, while the soil is still moist, pushing a shovel into the soil in spacings about 2 feet apart under the canopy. The shovel is pushed into the soil all the way and pushed forward so that the slit cut by the shovel is open. Then, drop some fertilizer into the open slit, pull the shovel out and push the slit closed with your foot. Irrigate immediately after you are finished.

If your trees are in a desert landscape with drip irrigation, then the whole idea of deep-root fertilizer comes into question .

Roots of trees and shrubs in a rock or desert landscape will not grow like they would in a lawn. Instead, with drip irrigation, roots grow profusely near the emitters and do not go "searching" for water or grow toward water. They are not psychics.

With drip emitters is best to drop your fertilizer in slits next to the emitters or use tree fertilizer stakes at the emitters.

Bob Morris is a horticulture expert living in Las Vegas; he is on special assignment in the Balkh Province, Afghanistan, for the University of California, Davis. Visit his blog at xtremehorticulture.blogspot.com.