How much water do you really need? When is the best time to water your vegetable? See our tips on watering your garden—plus, our Watering Guide listing critical times on when to water your crops and how much water they need.
According to some experts, less is often more when it comes to watering your vegetable crops. In areas without drought, a common mistake new gardeners make is watering too much!
Historically, gardeners have been advised to make sure that vegetables are getting an inch of water a week. The old rule of thumb of watering 1 inch per week originated from an understanding that, on average, it takes about 1 inch of precipitation at one time to deliver enough moisture to the deep root zone. In fact, this is not the case. For example, clay-based soils hold more water than sandier soils, so an inch of water a week could result in overwatering.
More important, there are methods and practices that can result in using less water but achieving better results with your plants.
Start With Good Soil
Cultivate Your Crops
Before the advent of hoses, water pumps, and trickle irrigation, farmers and gardeners practiced regular cultivation. Frequent cultivation prevents the wicking up process that draws water from the lower levels to the surface of the soil, where it is lost to evaporation. By aerating the upper layer of soil, cultivation also greatly improves the capture and retention of rainfall. Plus, it disrupts the germination and growth of weeds that would compete with crops for water.
Cultivate your garden early and often. A rototiller or push cultivator is good for large beds, but hand tools work fine in small plots. Alternate between fluffing up only the first inch or two of soil and tilling down 5 or 6 inches—always being careful not to disturb crop roots.
Timing is important: Many gardeners stop cultivating their gardens in midsummer once crops are established enough to out-compete weeds. But midsummer is the hottest time of year, when soil and plants are most vulnerable to moisture losses through evaporation and transpiration. Also, midsummer rains often come fast and furious, in the form of violent cloudbursts that dump a lot of rain in a short time. Frequent cultivation prepares your plots for dramatic percolation, allowing you to capture as much of that rainfall as possible, rather than have it run off or just puddle on the ground.
Traditionally, farmers and gardeners have cultivated their crops 3 days after a good, soaking rainfall to prepare the soil for the next rainstorm. And they often cultivate again just before a predicted thunderstorm.
After a rainfall, stay off (do not step into) freshly cultivated soil for 3 days. This will prevent soil compaction, allowing the rainwater to percolate down to the lower root zone. You want plants to root deeply so that they do not become dependent on surface watering.
Make Mulch Matter
Mulching is perhaps the #1 water-conserving technique for areas that receive less than 40 inches of rainfall annually. Organic mulches reduce evaporative moisture losses from the soil surface, and because the soil stays cooler, they also reduce transpiration water losses.
Mulching goes hand in hand with cultivation. After starting with bare ground, cultivate your crops in the early part of the season to keep the soil well oxygenated, until plants become established. If you are growing vining crops—cucumbers, melons, and squashes—apply mulch as soon as the plants begin to set runners. With fruiting crops such as tomatoes and peppers, wait until the blossoms drop and the plants begin to set their main crop.
Lose Your Guilt About Wilt
Temporary wilting during the heat of midday does not mean that it’s time to water. Some plants go through an obvious midday slump, which is an indication of the plant’s natural adaptation to its environment. Visit your garden again in the early evening and see if the wilted plants have regained some turgidity. If they have come back—that is, if they look perkier—do not water.
Don’t baby your crops: Plants are incredibly adaptable. They have the ability to draw water from deep in the soil. Periodically, take a trowel and dig down several inches into the zone where the roots are most active. If the soil there is still moist, there would be no benefit from watering.
How and When to Water
What you want in a healthy plant is deep root penetration, and the only way that you’re going to get deep roots is if there is water down deep.
Start at the very beginning: Saturate each plant hole when you transplant seedlings. When you do water, make sure that you get the soil saturated enough that the moisture percolates several inches down.
Believe it or not, sometimes the best time to water is during or immediately after a rainfall, especially if the rain shower amounts only to a half-inch or so of water. The reason for this is that you want to add sufficient water at the same time to ensure penetration down to 5 or 6 inches. If you wait another day or two to water, you will be adding only surface water, which evaporates rapidly. With only frequent, light watering (or rain showers), you never build up a reserve of water in the soil.
So, cultivate, mulch, and water in the rain. And learn from nature: Spend more time observing your garden and less time watering.
Watering Guide: Critical Times to Water and Amount of Water Needed
To address the big watering question, below is a chart that tells you critical times to water each vegetable crop as well as the number of gallons of water needed.
Of course, these guidelines assume that you have rich, well-balanced soil. Increase frequency during hot, dry periods.
|Needs a lot of water during dry spells.||Needs water at critical stages of development.||Does not need frequent watering.|
|Vegetable||Critical time(s) to water for a 5-foot row||Number of gallons of water needed|
|Beans||When flowers form and during pod-forming and picking||2 per week depending on rainfall|
|Beets||Before soil gets bone-dry||1 at early stage; 2 every 2 weeks|
|Broccoli||Don’t let soil dry out for 4 weeks after transplanting.||1 to 1 ½ per week|
|Brussels sprouts||Don’t let soil dry out for 4 weeks after transplanting.||1 to 1 ½ per week|
|Cabbage||Water frequently in dry weather for best crop||2 per week|
|Carrots||Before soil gets bone-dry||1 at early stage; 2 every 2 weeks as roots mature|
|Cauliflower||Water frequently for best crop.||2 per week|
|Celery||Water frequently for best crop.||2 per week|
|Corn||When tassels form and when cobs swell||2 at important stages (left)|
|Cucumbers||Water frequently for best crop.||1 per week|
|Lettuce/Spinach||Water frequently for best crop.||2 per week|
|Onions||In dry weather, water in early stage to get plants going.||½ to 1 per week if soil is very dry|
|Parsnips||Before soil gets bone-dry||1 per week in early stages|
|Peas||When flowers form and during pod-forming and picking||2 per week|
|Potatoes||When the size of marbles||2 per week|
|Squash||Water frequently for best crop.||1 per week|
|Tomatoes||For 3 to 4 weeks after transplanting and when flowers and fruit form||1 gallon twice a week or more|
How to Measure Your Water
If you set up a rain gauge or bucket in the garden, you can measure how much rain or irrigation water your garden is getting and time how long it takes your watering system— or a good steady rain—to drop an inch of water. Use a clean, empty tuna or vegetable can as a gauge. Measure its contents by putting a ruler into the water it collects.
For more on watering the garden, especially in drought, read our article on “The Water-Wise Garden.”