# What is the effect of watering on the temperature of the garden?

We have a large garden (<2 acres) that we are growing for the Post Falls, ID. food bank. The farmer is supplying the water. We have 5 zones across the garden and move the sprinklers three times to water the entire area. We are continually watering each zone for 12 hours, and then moving the sprinklers to the next section, water it for 12 hours, moving it to the next section and water it for 12 hours. We do not stop watering during the entire growing season.

It seems that the garden is not ripening as fast as gardens in the city. Can a garden's average temperature get lowered due to the watering, possibly delaying the harvest time?

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Have I got this correct, you water a zone (1 of 5) continuously for 12 hours, then move onto the next zone (2 of 5) for 12 hours of continuous watering? ie Each zone is watered continuously for 12 hours every 60 hours? If I have that correct, that to me seems like a lot! of watering, what exactly are you growing? – Mike Perry Sep 9 '11 at 2:56
+1 for "we are growing for the Post Falls, ID. food bank" – Mike Perry Sep 9 '11 at 2:57
Having re-read the question, does "5 zones across the garden" = 5 (sprinklers) watering zones? & you're able to water the whole garden once every 36 hours (3 x 12)? – Mike Perry Sep 9 '11 at 3:27
@MikePerry I believe he has 5 growing zones (different crops, perhaps) and 3 watering regions. Each watering region covers 5/3 of the zones (or 1/3 or the entire garden). – Lorem Ipsum Sep 9 '11 at 19:43
@MikePerry Yes, that is correct. From what he has said, they get it every 36 hours. – Lorem Ipsum Sep 9 '11 at 19:55

I agree with winwaed - you may be watering too much. Once plants are well-established, don't water until the soil is dry down to around an inch deep, or you see signs of water stress (typically, drooping leaves at first). Then water thoroughly enough that water's getting down the full root depth, and then some. This will vary with soil, etc. If it's hard to get that right all the time, or water cost is an issue, or summer heat stress is a problem even with plenty of water, consider using mulch to slow down soil evaporation and lower soil temperature. For the rest of this season, you may need to water somewhat more frequently because the plants are addicted - the root systems are probably very shallow.

I don't want to sound too diagnostic - without knowing your soil, climate, sprinkler, etc., it's impossible to tell for sure.

Too much watering will:

• cause shallow root systems that do poorly in hot weather or missed waterings
• cause fungal diseases
• waste water
• leach nutrients

Different plants like different conditions, but in general, cool roots and warm leaves is a good thing.

If fungal diseases become a problem, avoid watering late in the day - in cooler climates, you want the sun to evaporate standing water from the leaves before sunset.

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Watering lowers the soil temperature. If the water is cold, it can take quite a few hours before the sun warms the earth back up. Water evaporating from the soil's surface also lowers its temperature.

As the other answers have pointed out, you're over-watering. Solomon's book also has an entire chapter that discusses watering in great detail. I'd highly recommend getting a copy as it covers aspects of watering like requirements for different soil types, how to conserve soil moisture, etc.

Another resource that would be good for your situation (which goes beyond home/backyard gardening) is Eliot Coleman's book "The New Organic Grower". Even if you're not "Organic", it has a lot of excellent advice that is targeted to the scale at which you are growing.

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Watering could cool temperatures - because the water is cool, and (more importantly) through evaporation.

However, I think it is more likely you are simply watering too much, making the soil too wet. How often do other places water? Here in Texas (hotter and drier in summer), 30 mins or 60 mins watering in the evening is more common, and I typically water much less (balancing water conservation into the mix).

I would look into what other food growers in the area do, and try that.

Over-watering can also cause mineral / nutrient leaching.

You're probably already doing this, but are you making and applying compost? just checking - that could make a huge difference if you are not doing this.

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WE do some compost, but most is planted as is. I probably should measure the temperature at other locations and in the garden to see if there is much of a difference. I was hopeing that maybe a study was made on watering effect on temperature. – ronald voights Sep 9 '11 at 3:21
Evaporation of moisture can cool the surface through latent heat of evaporation. This can be sufficient to cause ground frosts when air temperatures get close to (but not quite at) freezing. – winwaed Sep 9 '11 at 3:36