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Plant Watering Calculator

Enter garden area, plant type, and climate — get weekly watering needs in gallons or liters

Area:
Volume:

About This Tool

Overwatering kills more plants than underwatering. But how much is enough? The answer depends on your garden size, what you're growing, your climate, and the season. This calculator takes the guesswork out of watering. Enter your garden or lawn area, select the type of plants, choose your climate zone, and get a weekly watering recommendation in gallons or liters. The calculator accounts for plant water needs, evaporation rates, and seasonal adjustments. Use it to plan irrigation systems, estimate water bills, or just figure out how long to run your sprinkler. Remember that rainfall counts — if you got an inch of rain this week, you need less supplemental watering.

How to Use

1. Enter your garden area (square feet or square meters) 2. Select the plant type (lawn, vegetables, flowers, shrubs, trees) 3. Choose your climate (arid, semi-arid, temperate, humid, tropical) 4. Select the current season 5. View weekly water needs in gallons or liters 6. Subtract recent rainfall from the recommendation

Formula

Base water need = Area × Plant water factor × Climate factor × Season factor Plant factors (inches/week): Lawn 1.0, Vegetables 1.5, Flowers 1.0, Shrubs 0.8, Trees 0.5, Succulents 0.2 Climate factors: Arid 1.5, Semi-arid 1.2, Temperate 1.0, Humid 0.8, Tropical 0.7 Season factors: Summer 1.3, Spring/Fall 1.0, Winter 0.5 1 inch of water per sq ft = 0.623 gallons

Frequently Asked Questions

How much water does a lawn need per week?
Most lawns need about 1 to 1.5 inches of water per week, including rainfall. In hot, dry climates, this can increase to 2 inches. A 1,000 sq ft lawn needs about 620 gallons per week to receive 1 inch of water. Water deeply and infrequently (2-3 times per week) rather than daily shallow watering.
When is the best time to water plants?
Early morning (6-10 AM) is ideal. The water soaks in before the heat causes evaporation, and leaves dry quickly which prevents fungal diseases. Evening watering is second best but can promote fungus. Avoid watering in the midday heat when up to 50% of water can evaporate before reaching roots.
How do I know if I'm overwatering?
Signs of overwatering: yellow leaves, wilting despite wet soil, root rot (mushy brown roots), fungus gnats, mold on soil surface, and edema (water blisters on leaves). If soil is constantly wet and plants look unhealthy, reduce watering frequency. Let soil dry between waterings.
How do I measure an inch of water?
Place several empty tuna cans or straight-sided containers around your lawn while watering. When they contain 1 inch of water, you've applied 1 inch to your lawn. Time how long this takes — that's your watering duration. Different sprinkler types have different application rates.
Do potted plants need more water than garden plants?
Yes, generally. Container soil dries faster than ground soil because it's exposed on all sides. Small pots dry faster than large ones. Terra cotta pots dry faster than plastic. Check potted plants daily in summer. This calculator is designed for in-ground gardens — increase recommendations 20-30% for containers.
How does mulch affect watering needs?
Mulch reduces watering needs by 25-50%. A 2-4 inch layer of organic mulch (wood chips, straw, leaves) reduces evaporation, keeps soil cool, and retains moisture. If your garden is well-mulched, you can reduce the calculator's recommendation by about 25%.
Should I water differently for clay vs sandy soil?
Yes. Sandy soil drains fast and needs more frequent watering with less volume each time. Clay soil holds water longer but absorbs it slowly — water slowly to prevent runoff, and water less frequently. The total weekly amount is similar, but the schedule differs.

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