How Much Water Does My Vegetable Garden Need?

comments (2) January 28th, 2014

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ChrisMcLaughlin Chris McLaughlin, contributor
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Photo by Beth Kingery under the Creative Commons Attibution License 2.0.Click To Enlarge

Photo by Beth Kingery under the Creative Commons Attibution License 2.0.

For some of us this is going to be a banner year for water conservation (ahem, California). So how much water are your vegetables going to need? First of all, most seeds will need to be kept moist until they germinate and the little seedlings show up. Transplants will also need frequent watering for the first two weeks after being moved to your garden bed.

I've never been satisfied with the typical garden advice of watering in "inches" simply because I have no way of truly measuring the water I give my gardens. While I'm certain that there's some wonderful math formula to calculate this, I'd rather let the plants tell me.


Shallow, Medium, and Deep Roots

Aside from the above special instances, it's usually the plant's root depth that will give you clues about their water needs. Soil will also play a major role, as well as the environment (weather). Soils that are rich with humus or compost will have good to excellent water retention, so you can get away with less water, while sandy soils will have you hose-in-hand more often.

Because the top few inches of soil dried out quickly, shallow-rooted vegetables such as cucumbers, spinach, cabbage, celery, corn, onions, leeks, carrots, broccoli, radishes, and Brussels sprouts will need frequent watering in hot weather or soils that are light on humus or compost. Here in California, on the hottest days of summer, my shallow-rooted veggies need water nearly everyday.

Vegetables with a medium root depth such as eggplant, beans, turnips, kale, lettuce, peas, peppers, potatoes, rutabagas, and summer squash will, of course, require moderate watering. While the deeply rooted plants such as watermelon, winter squash, pumpkins, parsnips, asparagus, okra, tomatoes, rhubarb, and sweet potatoes can reach down and tap into lower water reserves for moisture.


Important Watering Times

If you're actively conserving water in your vegetable garden this year, you should keep in mind that specific plants have their certain times when it's important for them to receive steady water. Vegetables that produce fruit such as tomatoes, peppers, watermelon, eggplant, pumpkin, and cantaloupe will need sufficient water during flowering and fruit development.

Turnips, parsnips, carrots, beets, and sweet potatoes need steady water while their roots (or bulbs) are growing; lettuce, cabbage, broccoli, cauliflower, and Brussels sprouts need focused watering while they leaves or heads (really unopened flowers) are developing; and radishes, Swiss chard, celery, kale, leeks, and mustard prefer to have consistent water throughout their life cycle.

Edited to add: In an effort not to confuse people who may have vegetable varieties that don't have the exact root measurements that I originally suggested, I've removed the estimated root depths.

posted in: vegetable garden, Water, water conserving

Comments (2)

ChrisMcLaughlin writes: daShrubber: Different varieties will play a role in root depth. For example, Thumbelina carrots will never reach the depth that Danvers will -- there's a huge variance there. So I can see how gardener's experiences will vary. The point still remains the same as far as shallow, medium, and deep for the most part.

I've been growing a wide variety of lettuces for about 20 years and I've never had any lettuce reach 3-4 feet deep! Once again, we all have our own specific experiences, I suppose taking the variety and soil into consideration.
Posted: 5:51 pm on January 29th
daShrubber writes: Very simplistic and a bit misleading. See the book Roots Demystified. Where did your list of root depths come from? The drawings in the book - based on actual diggings - show some of a lettuce's roots go to 3-4 feet deep.
Posted: 10:28 am on January 29th
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