Basic concepts by which you must irrigate:

1. Plant coverage partially determines water use rate. Plants take up water from the soil through their roots and lose it through their leaves. The more of the soil surface covered by leaves, the faster water will be pulled from the soil. There is some water loss from the soil surface, but it isn't much compared to the rate that is lost from the leaf cover.

NOTE: "An inch" of water is the way we measure applied irrigation water. If water applied to the soil would have built up to one inch deep if it had not soaked in, that is "one inch" of water. Plants6 generally use about 36-40 inches of water per season. If you scatter a few large, straight-sided containers (coffee cans) around under your sprinklers, and AN AVERAGE of one inch of water is caught during your sprinkling, this is considered an inch of water. Use more than one can to determine how long it takes to apply an inch, as there is a lot of variation under most sprinklers. It is important that you measure your irrigation water to avoid over or under-irrigating.

2. The rate of plant water loss from leaves is dependant on air temperature, humidity, wind and sunlight. Water use rate per day is low in April, (about .1 to .15 inches of water per day), picks up slowly in May (about .25 inch/day), then really starts to roll in June (about .25-.30 inch/day), peaks in July and early August (at about .33- .40 inch/day), then finishes out the summer at .25-.3 inches per day, and drops to about .12 to .2 inches per day in the cool of the Fall. So, if you water once a week, you will likely need 1/2 to 1 inch each irrigation in April, 1- 2 inches / week in June, 2-3 inches per week in July through the hottest part of August, then back to about 1 to 1 1/2 inches in the warmer parts of Fall. Unless your soil is real high quality, you are unlikely to be able to water only once a week when the plants are using high rates per day.

3. Your soil holds more or less "inches" of water, depending on its texture (sandy? moderate? silty? clay?), compaction (how deeply have you turned it?), and the depth of rooting of the plant.

4. The amount of water you apply each irrigation is determined by your soil quality, and/ or the amount that the plants may have used since your last irrigation.

5. When your plants need to be irrigated is related to both the water use rate and the water storage capacity of your soil. Most frequent irrigation (using lesser amounts of water per irrigation) is necessary on sandy soils in July. Least frequent irrigations (using greater amounts of water per irrigation) are required on finer textured soils or in the Spring and Fall on any soil.

6. To match your irrigation to water use, you must vary the number of hours you apply water, the number of days between irrigations, or both. Short irrigations of 15-30 minutes are generally a waste of water. When you apply water, make certain it soaks in, and you apply water adequate to recharge the soil deeply. People often irrigate the top 6 to 12 inches of soil, and allow the deeper soil to dry out. This is real tough on trees and shrubs, which generally root in the top 2 or three feet of soil. (They have deeper roots, but most of the action is up where the oxygen is plentiful.)

The soil should become moderately dry between irrigations to encourage plant health and fruit quality. Roots need air, and drying the soil sucks air down into it.

Irrigate watermellons about half as often as other mellons. THEY HATE WET SOIL!! They are native to African deserts.

As soon as the weather becomes reliably warm, you must irrigate carefully. Pay no mind to the generalized suggestions about watering that you see in the gardening mags. They usually suggest "about one inch of water per week" during the summer. This is not true. Water use starts slowly, but when the plants are little, and roots have not grown much, (in early May), they need frequent, but fairly light irrigations. "Frequent" is about every 4-5 days, "light" means about 1/2 to 3/4 inch of water, depending on warmth of the weather.

Once we get into the hot weather, and plants cover a larger percentage of the soil surface, they can use between 1/4 and 1/3 inch of water every day. This means you may need that inch of water on about every third or fourth day. If your soil is quite sandy, then replace the water about that frequency. Most soils will hold about 1 1/2 to 2 inches of water in the melon root zone, so you may need to apply that amount of water every 5 to 7 days during the highest summer heat. The number of days between irrigations can be reduced or increased if the weather is warmer or cooler than "normal".

As late summer approaches, and fruit begins to ripen, irrigate in the morning, and less. Some fruits may split if they take water to quickly when they are almost ripe.