IN the deep South, a colorful garden of majestic tulips swaying in a spring breeze is especially rare - and breathtaking. The warm zephyrs that lure winter-weary folk contribute to the problem of growing tulips, which need a period of cold temperature to trigger the blooms in spring. Until recently, only the Southern gardener with a healthy purse could afford a tulip display, since the investment was only for one season.
Tenacious Southerners, however, have been steadily working on the problem of how to include tulips in the spring marathon that continues from late January until May, when roses usher in summer.
Researchers at North Carolina State University have solved a major part of the problem. Using field trials, they have discovered a number of tulip cultivars that do well in Southern climates. Also they have found that the key to future blooms is a fertilization schedule that ensures bulb increase.
Basically, all tulips need initial ``cold treatment,'' which in a warm climate has to be artificially induced by preconditioning with at least 12 weeks of 45-degree temperatures before planting. A rule to keep in mind regarding cold storage time: If you shorten the time, you shorten the stem - and may blight the bud as well. So move the vegetables aside and begin cooling the tulip bulbs early. As soon as they appear in the nurseries, go get them.
Check bulbs carefully before buying. Large size is important, and be aware that bulbs are sometimes damaged when subjected to temperature extremes in transit or in storage.
A final note of caution: Certain fruits, such as apples, give off ethylene gas, thus bulbs don't coexist well with these. So don't store them together. If tulip cultivars for your area are available precooled, the best bet might be to buy these, or cool bulbs in an old refrigerator in the garage where no fruit is stored.
Because bulbs store their own supplies of nutrients, some assume that all a gardener need do is sprinkle a bit of bone meal in the planting hole, cover the bulb with dirt, and ``think spring.''
But according to Dr. Paul V. Nelson of the Horticultural Sciences Department at North Carolina State University, the first concern must be the pH level of the soil, which should be checked yearly. Southern soils are generally acidic, which makes the azaleas and pines happy, but not tulips. Below pH 5.4, tulips may develop a calcium deficiency. As with a great many plants, a pH between 6.0 and 7.0 pleases tulips. Your county extension agent will supply information on soil pH factors.
Plant bulbs where they will be sun-bathed and well drained. At planting time, mix a balanced fertilizer into prepared soil (organically enriched sandy loam) at the rate of five ounces each of nitrogen and potassium and four ounces of phosphorus per 100 square feet of the area. (Three pounds of 10-10-10 or four pounds of 8-8-8 would include the right proportions.)
At emergence, when shoots have just begun to appear, another five ounces of nitrogen alone is needed per 100 square feet. Either 15 ounces of ammonium nitrate; 25 ounces of ammonium sulfate; or 32 ounces of calcium nitrate per 100 square feet are possible sources for the nitrogen. Of course you can use the same 10-10-10 used at planting time, but the phosphorus and potassium will not be used by the plants and are thus wasted.
Another option that lessens the bother for a gardener is a commercial slow-release ``Bulb Booster.'' This product can be mixed into the soil at planting time and eliminates the need for fertilizing at emergence. In following years, all fertilizers should be top-dressed on the beds so as not to disturb the bulbs.
Never fertilize at flowering time or thereafter until fall. The nutrients are not only wasted, but the added nitrogen can foster fusarium fungus, which will attack bulbs when the soil heats up in summer.
For a list of tested varieties of cultivars that have performed well in specific zones in the South, send $2 payable to North Carolina State University to Bulletin 476, Publications, Campus Box 7603, Dept. of Agricultural Communications, North Carolina State University, Raleigh, NC 27695.