Frequency/amount to water

A set of interesting documents from the University of California Master Gardener Program. Both documents are downloadable PDF files. In addition to a good discussion on water needs, they give good sample calculations on the amount of water raised beds need.

1. How Much Water Does My Food Garden Need?

2. Food Gardening with Less Water

3. A More In-Depth Look at Food Gardening with Less Water

Scorpio Rising wrote:So. sick. of watering.

I know the feeling.  That is why I put in drip irrigation with a timer a few years ago. I'm getting too old for dragging around water hoses and watering cans.

The subject of how much water, and how often, came up today as a neighbor new to gardening asked how much water the vegetables need. I told him that in general vegetables need 1" of water per week, with a couple exceptions -- those exceptions are cucumbers and eggplant. Both cucumbers and eggplants need 1" of water per week until they set fruit, and then they need 2" of water per week. The reason cucumbers and eggplants need 2" of water when they set fruit is because their fruit is almost all water.

But, how much water is 1" in the garden. That is easy to calculate by converting cubic inches to gallons: 12"x12"x1" equates to 0.62 gallons of water. That means to provide 1" of water to a bed would need 0.62 gallons of water per square foot - a 4'x8' bed, then, would need 20 gallons of water to provide 1" of water to that bed.  Twenty gallons sounds like a lot of water, but if you water 4 times a week, that is only 5 gallons of water each time, or if you water 3 times a week that would be 6.6 gallons each time.

With my drip irrigation I have to count the number of drip emitters in the bed, each providing .5 gph, to calculate how long the timer must run the water to provide that 5 gallons of water.

lisawallace88 wrote:Wow, just over half gallon per week? my tomatoes are demanding more water and they are getting prob a gallon each every 2nd day (for now-will increase to every other day when the real heat of the summer arrives) but they are in grow bags.

Yes, good point, but it is important to remember that the "one inch of water per week" is a measurement of water available to the plants. Water that runs off or evaporates is not available to the plants, likewise water that is below the root zone is not available to the plants. It is important to have heavy mulching that keeps the soil cool and contain the moisture, just as it is important to apply the water directly to the soil and not sprayed into the air.