The winter was the deep-freeze kind, but fruit trees are responding to the extra heat March has brought. Flower buds on apricots and plums are preparing for their fruit producing role.

To answer a frequently asked question, although not the topic of the day: A little color showing on the developing bud indicates the time is right for the delayed dormant spray. Purchase a supreme or superior spray oil. Volck is readily available. Mix the recommended rate of diazinon or thiodan insecticide with it and apply the combination to every branch, twig and bud to help control overwinter insects such as aphids, scales and mites.Right now another question of home (and commercial) orchardists is: "How can I be sure to get a fruit crop - the weather forecast is for frost tonight?"

There is, to be practical, little you can do in the lopsided battle with a formidable foe, Mother Nature.

Let's first consider the need for protection. Fruit trees produce several times more blooms than can possibly mature into ripe fruit. Some thinning accomplished by frosts will save you a lot of time and work later. The frost of a night or two may not affect the total fruit crop because of the difference in bloom opening. If you look carefully, you'll see some unopened buds even though it looks like "popcorn popping on the apricot tree."

Information coming out of Washington State University research indicates fruits will tolerate lower temperatures than previously thought. I've extracted some figures that indicate how cold it must get to kill 50 percent of fruit buds at various stages of development. These values are from an accurate thermometer with a cover over it to avoid the nighttime radiation effect. Damage is greater, of course, if the low temperatures persist for longer periods of time.

DELAYED DORMANT: (apricots and plums about now). Bud scales widely separated but still attached. Leaf tips on apples showing. Pear and cherry blossom buds exposed.

Red Delicious - 17

Golden Delicious - 16

Pears - 19

Cherries - 25

Apricots - 18

Peaches - 20

FULL BLOOM:

Red Delicious - 25

Golden Delicious - 24

Cherries - 26

Bartlett Pears - 25

Apricots - 23

Peaches - 25

Prunes - 21

SMALL GREEN FRUITS:

Apples - 27

Pears - 26

Cherries - 27

Peaches - 27

Apricots - 27

Plums and prunes - 25

There are certain microclimates to consider. Buildings may offer some nighttime protection as could expanses of asphalt or concrete. Bare soil will release more of the heat that it has absorbed during the daytime than will a grass covering. Trees at the bottom of a slope may be in the cooler part of the yard because cold air "runs" downhill.

The air is colder close to the ground on a calm, clear night. The temperature at a 5-foot level may be 10-15 degrees warmer than near the soil. Taller trees may have blossoms that survive, even though most will be killed in the lower part of the tree. Gentle winds may have a mixing effect, and warmer, upper layers may save the fruit crop. That's the principle behind the commercial orchardist's use of wind machines.

The home orchardist can provide only a limited amount of protection if temperatures reach the point that can damage the fruit at various stages. The easiest operation, according to some orchardists, is to put up their Christmas lights on the fruit tree branches. If a bud happens to be right next to a light, it may survive, but in general this practice is an exercise in futility.

Covering the tree comes to mind also. However, any but the smallest tree (possibly not blooming yet anyway) will take a larger expanse than you realize. Blankets or quilts may provide a limited insulating value and trap some heat rising from the soil on very small trees.

Larger trees mean larger sheets and plastic is the most common material readily available. A single layer of plastic does little good to keep heat in and, unless it is removed during the day, will probably do more harm than good. A tree covering may provide a trap for a heat source placed under the tree to gain a few degrees protection. But have you ever handled a large sheet of plastic and tried to get it over branches of a tree several feet higher than your head? And what heat source is cost effective? Electricity and kerosene add up pretty fast.

If I were to try and save my fruit crop, I would try water. Sprinkling can provide considerable freeze protection - probably to 25 degrees or so. The ice that forms in freezing weather is not insulating. The protection is from the "heat of fusion" as water turns to ice. The released heat is transferred to the plant tissue and keeps the buds at 32 degrees, above the damaging temperatures. You need to keep the water running to cover the trees from the time air temperature reaches 32 degrees until the ice has melted. The coolest temperature is usually just before sunrise.

Some drawbacks to sprinkling include:

- Obtaining a sprinkler that will apply only one-seventh to one-eighth inch of water per hour. Most sprinklers put on twice that rate.

- You may damage the tree with a load of ice that forms. Unless you have pruned to develop a strong limb structure, breakage will be common.

- The soil around that part of the yard may turn into a quagmire with several nights of sprinkling. Tree roots may be damaged if drainage is poor.

- Some tree diseases may be encouraged by the excessive water application.

A total crop loss is rather uncommon if you are where tree fruits are ordinarily recommended. Preserve an extra year's supply when fruit is abundant. Occasionally you'll be spared the drudgery of spraying, picking and processing and will be able to accomplish something you've always wanted to do to enrich your life!

FREE WORKSHOPS

March 29, 7 p.m., "Lawn Managment."

Planting, fertilizing, mowing, etc. Extension Office Training Room S1010 South Building County Government Center (CGC), 21st South and State. Enter by northeast double glass doors.

April 4, 7 p.m., "More Vegetables from a Small Space."

Granger Bishop's Storehouse, 3648 S. 72nd West.

April 5, 2 or 7 p.m. Same topic, CGC.

(Note new dates for "Gardening in a Drought.")

April 11, 3 p.m., "Gardening in a Drought." (CGC)

7 p.m. Same topic. Granger Bishop's Storehouse.

April 13, 3 or 7 p.m. Same topic CGC.