Free vegetable garden water calculator. Enter how many beds you water to find the water you use each week and each 4 week month.
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Enter the number of garden beds. This calculator allows 20 litres of water per bed per week, then multiplies by 4 for a 4 week month.
Most vegetable gardens need about 1 inch of water per week, including rainfall. One inch over 1 square foot is about 0.623 gallons, so a 10 square metre bed at 1 inch per week needs roughly 250 litres per week. Hot dry weather can raise demand to 2 inches or more, while cool cloudy weather can drop it below 1 inch. This calculator uses a simpler planning figure, 20 litres per bed per week, which suits a small raised bed in average weather.
The Old Farmer Almanac table gives gallons per week for a 5 foot row: beans 6, cabbage 6, corn 6, cauliflower 6, celery at least 6, tomatoes 6, peppers 3 to 6, potatoes 3 to 6, carrots 3 early and 6 as roots mature, beets 3, peas 3, onions 3, lettuce and leafy greens 2, cucumbers at least 3, squash at least 3. Water demand rises at critical stages: beans at flowering, corn at tasseling, tomatoes from flowering until harvest.
Water deeply two or three times a week rather than a little every day. Deep watering soaks the root zone 6 to 8 inches deep and grows deeper, stronger roots, while frequent shallow watering leaves weak roots near the surface. Check the soil 1 to 2 inches below the surface: if it is dry there, water. Midday wilting alone does not always mean thirst, since leaves can wilt in heat and recover by evening.
Watering frequency depends on soil type. Sandy soil drains fast and needs water every 2 to 3 days in smaller amounts. Loam holds water well and suits a deep soak every 3 to 4 days. Clay holds water longest and needs a slow deep soak every 4 to 7 days. Raised bed mix dries faster than open ground and needs water every 2 to 3 days in warm weather. Containers dry fastest of all and often need water daily in summer.
Water early in the morning when temperatures are cool and evaporation is low, so foliage dries during the day. Evening watering is an acceptable second choice, but wet foliage overnight can encourage fungal disease. Avoid midday watering, when much of the water evaporates before it reaches the roots. A 2 to 4 inch layer of organic mulch retains moisture, keeps roots cooler, and often stretches the watering interval by several days in hot weather.
Drip irrigation and soaker hoses are the most efficient way to water a garden, because they deliver water directly to the roots with little waste. The run time formula is: water requirement in gallons equals area in square feet times water depth in inches times 0.623, and run time in hours equals water requirement divided by the application rate in gallons per hour. A worked example: a 50 square foot bed at 0.5 inches per session with 25 emitters at 1 gallon per hour each needs about 15.6 gallons, so run time is about 37 minutes per session.
In this calculator, 1 bed plans 20 litres per week and 80 litres in a 4 week month. Five beds plan 100 litres per week and 400 litres per month, and 10 beds plan 200 litres per week and 800 litres per month. To compare with inch based guides: a 4 foot by 8 foot bed is 32 square feet, and at 1.5 inches per week it needs about 30 gallons that week. A standard hose delivers about 15 to 20 litres per minute, so 250 litres takes around 15 minutes of hose time.
Underwatered plants wilt, yellow from the base, and grow slowly, and their soil feels dry 2 inches down. Overwatered plants also yellow, but their soil stays soggy and roots can rot. The screwdriver test helps: a screwdriver slides about 6 inches into moist root zone soil with little resistance, but stops short in dry soil. A rain gauge or a tuna can marked at 1 inch shows how much rain and irrigation a bed actually received in a week.
About 1 inch per week on average, or about 20 litres per bed per week as a planning figure in this calculator. Hot dry weather can raise it to 2 inches or more.
Deeply two or three times a week, depending on soil type and weather. Sandy soil needs water every 2 to 3 days, loam every 3 to 4 days, and clay every 4 to 7 days.
Deeply a few times a week. Deep watering soaks the root zone 6 to 8 inches deep and builds stronger roots than daily shallow watering.
Multiply area in square feet by inches of water by 0.623. A 32 square foot bed at 1.5 inches needs about 30 gallons per week.
Check soil 1 to 2 inches below the surface. If it is dry there, water. A screwdriver that slides 6 inches in easily means the root zone is moist.
Evening watering is acceptable, but morning is better, because wet foliage overnight can encourage fungal disease. Avoid midday watering, when evaporation is highest.
Yes. A 2 to 4 inch layer of organic mulch retains moisture, keeps roots cooler, and often stretches the watering interval by several days in hot weather.
A mature tomato in open ground needs about 4 to 6 litres per week in warm weather, up to 8 litres in hot dry conditions. In containers, allow 2 to 3 litres per plant per day.
Divide water requirement by application rate. A 50 square foot bed at 0.5 inches per session with 25 emitters at 1 gallon per hour runs about 37 minutes per session.
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