Water the right amount, not more. This chart gives you weekly water needs by crop, climate multipliers, and irrigation efficiency factors so you can stop guessing and start watering with confidence.
1. The Core Formula
Water Needed (gal/week) = Area (sq ft) × Water (in) × 0.623
Actual Water to Apply = Water Needed ÷ Irrigation Efficiency
(1 inch of water over 1 sq ft = 0.623 gallons)
2. Weekly Water Needs by Crop
| Crop | Water (in/week) | Category | Notes |
|---|---|---|---|
| Lettuce, Spinach, Kale | 0.5–1.0 | Low | Shallow roots; water lightly, often |
| Radishes, Peas | 0.75–1.0 | Low–Medium | Keep evenly moist |
| Carrots, Beets | 1.0–1.5 | Medium | Consistent moisture prevents cracking |
| Tomatoes | 1.0–1.5 | Medium | Deep roots; water deeply 2–3×/wk |
| Peppers, Eggplant | 1.0–1.5 | Medium | Sensitive to over-watering |
| Beans (bush & pole) | 1.0–1.5 | Medium | Critical during flowering & pod set |
| Cucumbers | 1.5–2.0 | High | Bitter fruit = water stress |
| Squash, Zucchini | 1.5–2.0 | High | Large leaves lose lots of water |
| Corn | 1.5–2.0 | High | Critical at tasseling & silking |
| Melons, Watermelon | 1.5–2.5 | Very High | Reduce slightly as fruit ripens for sweetness |
| Okra | 1.5–2.0 | High | Heat-loving; drought-tolerant once established |
| Potatoes | 1.0–1.5 | Medium | Uneven water causes hollow heart & scab |
| Onions, Garlic | 0.75–1.0 | Low–Medium | Stop watering once tops begin to fall |
| Herbs (basil, etc.) | 0.75–1.0 | Low–Medium | Let soil dry between waterings |
| Strawberries | 1.0–1.5 | Medium | Critical during fruiting |
3. Climate Adjustment Factors
| Climate | Multiplier | Typical Regions | Effect on Water Needs |
|---|---|---|---|
| Cool / Maritime | 0.7× | Pacific NW, coastal NE | Reduces needs by ~30% |
| Temperate | 1.0× | Midwest, mid-Atlantic | Base (no adjustment) |
| Hot / Dry | 1.3× | Southern plains, interior West | Increases needs by ~30% |
| Desert / High Heat | 1.5× | Southwest, deep South summer | Increases needs by ~50% |
Hot, dry, and windy conditions increase evapotranspiration (water lost from soil + plant leaves). Use the multiplier that best matches your summer conditions.
4. Irrigation Method Efficiency
| Method | Efficiency | Water Lost | Best For |
|---|---|---|---|
| Drip irrigation | 92% | 8% | Raised beds, rows, containers — most efficient |
| Soaker hose | 75% | 25% | Rows, beds; low-cost drip alternative |
| Hand watering (wand) | 70% | 30% | Small gardens, containers |
| Sprinkler (above-ground) | 65% | 35% | Large areas; loses most to wind & evap |
Lower efficiency means you apply more water to deliver the same amount to the roots. Divide your needed gallons by the efficiency (e.g., 100 gal needed ÷ 0.65 = 154 gal to apply with a sprinkler).
5. Water Needs for Common Garden Sizes (1 in/week, sprinkler)
| Garden Size | Area (sq ft) | Gal/week at roots | Gal to apply (65% eff.) | Min/week (10 gpm hose) |
|---|---|---|---|---|
| 4 × 4 ft bed | 16 | 10 gal | 15 gal | 1.5 min |
| 4 × 8 ft bed | 32 | 20 gal | 31 gal | 3 min |
| 10 × 10 ft plot | 100 | 62 gal | 96 gal | 9.6 min |
| 10 × 20 ft plot | 200 | 125 gal | 192 gal | 19 min |
| 20 × 30 ft plot | 600 | 374 gal | 575 gal | 58 min |
| 1,000 sq ft garden | 1,000 | 623 gal | 958 gal | 96 min |
Assumes 1 inch of water per week with a 65%-efficient sprinkler and a 10 gal/min garden hose. For 1.5 in/week, multiply values by 1.5. For drip (92% eff.), divide the "gal to apply" by 0.92/0.65 ≈ 1.42.
6. Watering Best Practices
🌅 Water in the Morning
Early morning (5–8 AM) minimizes evaporation and gives foliage time to dry before evening, reducing fungal disease.
📏 Deep & Infrequent
Apply 1–2 inches at a time, 2–3 times per week. Shallow daily watering creates shallow, weak roots.
👆 Finger Test
Stick your finger 2 inches into the soil. If it's dry at that depth, it's time to water. If damp, wait.
🌧️ Track Rainfall
Use a rain gauge. Subtract weekly rainfall from your crop's water needs before irrigating — most gardens get 1+ in/week in summer.
🍃 Water the Soil, Not Leaves
Wet leaves invite fungal blight. Use drip, soaker hoses, or aim water at the base of plants.
🛏️ Mulch Heavily
2–3 inches of organic mulch (straw, wood chips) can cut watering needs by up to 50% by reducing evaporation.
🍅 Adjust by Stage
Seedlings need frequent light water. Fruiting crops need the most. Reduce water as crops near harvest to concentrate flavor.
🌡️ 1 Inch = 6–8 Inches Deep
One inch of water typically penetrates 6–8 inches into loam soil. Sandy soils need more frequent watering; clay soils less.
7. Quick Conversions
| Convert | Multiply By | Example |
|---|---|---|
| Inches of water → gallons | × 0.623 / sq ft | 1 in × 100 sq ft = 62.3 gal |
| Cubic feet → gallons | × 7.48 | 1 cu ft = 7.48 gal |
| Cubic feet → cubic yards | ÷ 27 | 27 cu ft = 1 cu yd |
| Gallons per minute (hose) | ~10 gpm | 10 min = 100 gal |
| 1 cubic yard of water | ≈ 202 gallons | — |