Enter your bed size to find out exactly how many litres or gallons of water your garden needs each week — and how much less you need after rainfall.
Length and width in metres or feet. Add the number of beds if you have more than one.
Most gardens need 2.5 cm (1 inch) of water per week. Enter how much rain already fell.
We calculate litres and gallons needed — total and after subtracting rainfall.
The widely accepted rule of thumb is 2.5 cm (1 inch) of water per week — including rainfall. This figure applies to most vegetables, annual flowers, and established shrubs. It is a starting point, not a fixed rule — different crops, soils, and climates all affect actual need.
The most reliable way to know exactly how much water your garden receives is to place a rain gauge or an empty straight-sided container in your garden. After each rainfall or watering session, measure the depth of water collected. If you've received 1.2 cm of rain this week and your target is 2.5 cm, you only need to apply 1.3 cm yourself.
Hot and windy weather increases evaporation significantly. In summer heat waves, many gardeners find they need to water more frequently — every 2–3 days — rather than delivering the full week's water in one go. Splitting the same total volume into smaller, more frequent sessions reduces evaporation and improves root uptake.
| Crop type | Water per week | Notes |
|---|---|---|
| Leafy greens (lettuce, spinach) | 2.5–3.5 cm | Shallow roots, dry out quickly |
| Tomatoes | 2.5–5 cm | More in fruiting period; consistent moisture prevents blossom end rot |
| Root vegetables (carrots, beets) | 2–2.5 cm | Deep but infrequent watering encourages downward root growth |
| Courgettes / squash | 2.5–5 cm | Heavy feeders and drinkers during fruiting |
| Herbs (basil, parsley) | 1.5–2.5 cm | Mediterranean herbs (rosemary, thyme) need even less |
| Beans & peas | 2.5 cm | Critical during flowering and pod formation |
Most vegetables and annual plants need about 2.5 cm (1 inch) of water per week — from rain or irrigation combined. This depth of water soaks the top 15–20 cm of soil, reaching the active root zone of most crops. Mediterranean herbs and drought-tolerant plants need less; heavy-fruiting crops like tomatoes and squash may need more in peak season.
Place a straight-sided container (a tin can or plastic cup works perfectly) in your garden bed. After rain or after watering, measure the water depth inside with a ruler. This tells you exactly how many centimetres or inches your garden has received. Empty and repeat each week.
Deep, infrequent watering is almost always better. Watering deeply once or twice a week encourages roots to grow downward in search of moisture, making plants more drought-resilient. Daily shallow watering keeps the top of the soil wet but leaves lower layers dry, encouraging shallow surface roots that suffer quickly in dry spells.
Yes, significantly. Sandy soil drains very quickly and needs more frequent watering to keep moisture in the root zone. Clay soil holds water much longer but can become waterlogged if over-watered. Loamy soil — a balance of sand, silt and clay — is the ideal growing medium and holds moisture well without becoming boggy.
Early morning is best. Water applied in the morning has time to soak into the soil before the heat of the day increases evaporation. Leaves that get wet in the morning also dry out quickly, reducing the risk of fungal disease. Avoid watering in the middle of a hot day — water evaporates too quickly. Evening watering is acceptable but leaves plants wet overnight, which can encourage mildew.
Mulch is the single most effective way to reduce watering frequency. A 5–8 cm layer of wood chips, straw, or compost on the soil surface dramatically slows evaporation, keeping moisture in the ground for much longer. Grouping plants with similar water needs together, and growing drought-tolerant varieties in exposed areas, also reduces overall demand.
The calculator works by multiplying your bed area by the target watering depth to get a total volume of water. This is the amount of water that needs to fall on — or soak into — the bed each week.
The formula (metric):
Area (m²) = Length × Width
Volume (litres) = Area × Depth (cm) × 10
To apply (litres) = Volume × soil factor − rainfall volume
1 cm of water over 1 m² equals 10 litres. 1 gallon = 3.785 litres.
For a 1.2 m × 2.4 m raised bed targeting 2.5 cm per week with no rainfall: 1.2 × 2.4 = 2.88 m² × 2.5 × 10 = 72 litres per week (about 19 US gallons).
Drip irrigation
Drip lines deliver water directly to the root zone at a slow, steady rate. This eliminates evaporation from leaf surfaces and reduces the chance of fungal disease. Drip systems typically use 30–50% less water than sprinklers for the same growing area.
Soaker hoses
A more affordable alternative to drip irrigation, soaker hoses weep water slowly along their full length. Lay them at the base of plants and cover with mulch for best results. They work best in straight raised beds rather than winding borders.
Watering by hand
Watering by hand with a watering can gives you the most control. Use a rose head to spread water gently, and aim at the soil rather than leaves. It takes more time but lets you observe your plants closely and spot problems early.
Rainwater harvesting
Collecting roof runoff in a water butt reduces your mains water use and gives plants slightly acidic water they prefer. A 200-litre water butt fills quickly in moderate rain. Position it near your beds to reduce carrying distance.
Mulching to retain moisture
A thick layer of mulch — bark chips, straw, or grass clippings — reduces surface evaporation by up to 70%. Apply 5–8 cm around plants once the soil is moist. This single step can halve how often you need to water in summer.
Everything you need to plan and grow a productive garden.
The EdenVatika app connects to your local 7-day forecast and generates watering tasks automatically. Dry spell ahead? Reminders appear. Rain expected? Tasks are skipped. No manual calculating required.
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Track every bed and planting
Log what's growing and get crop-specific care reminders
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