COLUMN: GARDENING: Many gardening needs to be addressed at this time of year

c If you have gardening questions, call the Master Gardeners' hot line at 257-5555 between 9 a.m. and 4 p.m., Monday through Friday. There is also a Web site at http://

ExtremeHort@aol.com.

This is one of the busiest times of the year for gardeners. The following needs to be addressed now: crabgrass and spurge control in lawns with preemergent weed killers, dormant oil applications for aphid control on fruit trees and roses, fertilizing fruit trees and other woody plants, last-minute pruning before new growth, planting of bare root plants, soil preparation and planting of summer color. Let's quickly cover them.

Fruit trees and other woody plants need their fertilizer application in the ground when new growth starts in the spring. The fertilizer needs to be near the root zone and watered in so that it can release nutrients into the soil water. The plant starts pulling in this water in high volumes as soon as leaves begin to appear. Basically the plant takes in whatever is in the water in the soil. If fertilizer isn't there, it can't take it in. It is so very important to have fertilizer available in this way at this time of year. In particular iron fertilizers or fertilizers containing iron must be applied now if you haven't done it. Which iron fertilizer is best? The iron chelate (pronounced "kelate") containing EDDHA will work the best. I used to tell

people Organo's KeRex was the one to buy, but I noticed they started using a different chelate a few years back that wasn't as good. You can check the label and see if they have changed back to EDDHA. Your informed nursery salesperson should be able to help you.

Aphid control. They are hiding, clustered around buds and waiting of new, soft succulent new growth to appear. They will then move from their overwintering spots to this new growth, which is easier for them to feed from. They then reproduce quickly to cover the new growth. Horticultural oils when applied properly cover soft-bodied insects like aphids and scales in the crawler stage and suffocate them. Oils should be applied when you know you will have a couple of days of warm weather. Applying them in the cold of winter will not be effective. Applying oils when it is hot may damage plants. Crabgrass and spurge. I never like to recommend pesticides (pesticides are anything that controls a pest and I consider crabgrass a pest) unless there really isn't any other alternative. In the case of crabgrass and spurge (that net-like, prostrate, purple plant with white sap) the best defense is to have a dense lawn mowed tall. But if you had bad problems last year with these weeds and you haven't done anything to improve the lawn then they will be back. There are some very good pre-emergent weedkillers you can use to control these pests provided you get these chemicals down now with good coverage. This would require a drop spreader on your part or a professional applicator who will probably apply the chemical as a liquid. In preparation for the application mow the grass to its desired height before applying then follow the label directions exactly. If the chemical is not a weed-and-feed type, then fertilize the lawn before you apply the weedkiller. Light applications of water (two to five minutes) are usually needed to wash the weedkiller onto the soil surface where it kills weeds as they are germinating from overwintering seed. Overwatering will ruin your application. If you still have living crabgrass that has made it through the winter it would be best to eliminate these plants by hand digging.

We had our very typical warm spell this year at the beginning of February instead of the end of January this year. If your tall fescue lawn got a bit brown this winter you probably did not put enough nitrogen fertilizer down in late fall to keep it green. You probably won't get it green again until it stays warm for a couple of weeks in a row. A few days of warm weather won't be enough. You could apply a normal application of nitrogen in anticipation of warm weather. Ammonium nitrate is one of the best nitrogen fertilizers for cold weather. Use no more than three pounds of this fertilizer for every 1,000 square feet of lawn. But be sure to get a good quality lawn fertilizer for the rest of the year. This would be a 21-7-14 or a fertilizer with a similar ratio of nitrogen, phosphorus and potassium. At least half of the nitrogen should be slow release. The bag will state that on the label under the nitrogen content if the nitrogen is slow release. Otherwise the manure-based fertilizers are terrific.

Question: How long should tree wraps be left on trees? Can you spray over the top of these wraps for borers?

Answer: Wraps are usually used to protect the tree from sun damage on the south and west sides of the trunk. The best protection is to leave enough foliage on the tree to shade the trunk during the summer months when most of the damage occurs. Wraps should be left on at least during the first year after transplanting. Larger trees may need to be wrapped longer. Leave wraps on long enough to last until the tree has recovered from transplant shock. This may take up to three or four years in the case of 36-inch boxed trees or larger.

Some tree wraps may not give the tree the kind of protection that you might think. Dark-colored tree wraps may actually cause more damage than if you left the tree unwrapped. The best color is white or reflective wraps. Avoid placing any kind of petroleum product on the trunk. Thin-barked trees such as palo verde, acacia, honey locust, stone fruit trees and their relatives, some ash like Modesto, crape myrtle, and others would probably benefit from some sort of wrap. One of the best methods is to use white wash or diluted white latex paint but it can really look tacky. Yes you can spray over the top of tree wraps but if they are plastic, you might be wasting your money.

Q. I read an article in the paper about houses being built on expansive soils in Las Vegas and the damage that can result. How do I know if I have an expansive soil and what can I do about it?

A. Expansive soils are soils that contain clay particles that expand when they become wet and contract when they dry out. You may have seen pictures of dry ground with huge cracks on the surface. These cracks can open to a depth of several feet. When wet, this same soil expands and the cracks disappear. These are pictures of extreme cases of expansive soils. You can imagine what would happen to structures built on these types of soils. Not all types of clays will do this. Soils containing clays that are expansive will cause heaving to occur on foundations, driveways, patios, sidewalks and other permanent structures after repeated wet and dry cycles. Expansive soils are usually

determined by civil engineering companies that specialize in soil analysis. This is supposed to be done before development of the property. If soils contain too much expansive clays, they are unsuitable for building certain types of structures or modification of the structure is required. Contact the Natural Resources Conservation Service at 388-6426 if you need additional assistance on expansive soils. They have maps that identify where these soils are principally located in the Las Vegas Valley.

This isn't the only problem that we have with our soils in this valley. Our soils contain high levels of salts such as gypsum that can dissolve with irrigation water and cause our soils to collapse. It can be a principle reason for walls and foundations to crack. A good reason for dry landscaping in these problem areas.

Bob Morris is area horticulturist, University of Nevada Cooperative Extension.