How much water per day for a tomato plant in a pot?

TL;DR - How much water for a potted tomato?

A normal tomato plant in a 15-20 litre pot needs about 500-800 mL of water per day, depending on:

• Pot size (small=less, large=more)
• Soil type (clay dries slower than sand)
• Temperature (warm=more water)
• Growth stage (flowering/fruiting=more than vegetative)

Rule of thumb: The soil should feel moist, not waterlogged. Test with your finger: poke 2 cm deep into the soil. Dry? Water. Still wet? Wait.

Why tomatoes in pots need so much water

A tomato plant in a pot cannot develop deep root systems like it would in the ground. All roots sit in a limited amount of soil, so water needs are higher. On hot summer days, potted plants may need watering twice a day. The pot also cannot draw water from deeper layers - you are entirely responsible for what you provide.

Additionally, water evaporates from a pot faster than from soil. The sides of the pot warm in the sun, speeding up evaporation. A dark terracotta pot warms faster than a white plastic pot.

Which pot size, which water needs?

The size of your pot determines how much water your tomato needs per day.

Small: 5-7 litre pot

• Only for very young seedlings or dwarf tomatoes
• Water needed: 200-300 mL per day
• Stays moist for only a short time
• Not recommended for mature fruiting tomatoes

Standard: 15-20 litre pot

• Standard size for tomato growers
• Water needed: 500-800 mL per day
• This is the "goldilocks" pot: large enough for nutrition and moisture, small enough to warm water directly
• Fits well in a balcony box or garden tub

Large: 25-30 litre pot

• For extra production or if you cannot water daily
• Water needed: 1000-1200 mL per day
• Larger moisture buffer
• Heavy to move

Very large: 40+ litre (planter box)

• For multiple tomatoes or very long growth
• Water needed: 1500+ mL per day
• Provides soil-like water stability
• Nearly as good as in-ground, but still not true soil

Water needs by temperature and season

Water needs also depend heavily on weather. A potted tomato in May needs far less water than the same plant in August.

May (growth, mild weather)

• Daytime temperature: 15-20°C
• Water needed: 300-400 mL per day
• Soil dries slowly
• Checking once daily usually suffices

June-July (growth, warm weather)

• Daytime temperature: 20-25°C
• Water needed: 600-900 mL per day
• Soil dries quickly
• Check twice daily, especially in mornings
• During heat waves, watering twice may be necessary

August (production, sometimes very hot)

• Daytime temperature: 22-28°C
• Water needed: 800-1200 mL per day
• Peak evaporation time
• Water early in the morning before it gets too hot
• Extra needs: during fruit setting, tomatoes are thirsty

September (finishing, cooler)

• Daytime temperature: 15-20°C
• Water needed: 400-600 mL per day
• Plant focuses on ripening, not growth
• Water slightly less
• Risk of root rot from excess moisture increases

How to water: methods and timing

Not all watering is the same. How you water affects how well the plant absorbs it.

Moisture check method (most accurate)

Stick two fingers about 2 cm deep into the soil next to the stem.

• Feels dry: Water now.
• Feels moist but not soggy: Wait.
• Feels like a wrung-out sponge: Perfect.

This works every time, without thermometers or experience.

Morning watering (recommended timing)

Water early in the morning, as soon as it gets light (06:00-08:00).

• Roots have focused on growth overnight without evaporation
• Morning water ensures the plant can absorb nutrients all day in the heat
• Leaves dry quickly, reducing fungal disease risk
• By evening, your tomatoes are fully hydrated

Evening watering (less ideal, but sometimes necessary)

In very hot summers, a second watering in the evening may be needed.

• Water only if the soil truly feels dry
• Evening water leaves leaves wet overnight, increasing fungal disease risk
• Limit to very hot days (>28°C)
• Use less than morning watering (e.g., 200-300 mL, not full dose)

Bottom watering (for pots in trays)

Place small pots in a water tray with 2-3 cm of water.

• The pot absorbs water from below
• Less leaf wetting risk
• Prevents fruit cracking from sudden water swings
• Check daily that water remains in the tray

Symptoms of too much and too little water

How do you know if your tomato is getting the right amount of water?

Too little water:

• Leaves wilt and close mid-afternoon, but recover by morning
• Soil cracks and pulls away from the pot edge
• Fruit develops radial cracks because water supply suddenly increases
• Plant grows slowly, no new leaves
• Flowers drop without setting fruit

Too much water:

• Roots rot; entire plant suddenly wilts even during heat waves!
• Lower leaves yellow; green colour only remains high
• Black or brown streaks on stems (root rot/phytophthora)
• Moisture-loving pests and fungi increase
• Fruits crack and split (chaotic water management)

Ideal condition: tomato wilts very slightly mid-afternoon in hot sun, but fully recovers by morning after watering.

Calculator: how many millilitres of water today?

Use this simplified formula for your situation:

Pot size x Temperature factor = mL water today

Pot size:

• 5-7 litre = multiply by 0.3
• 15-20 litre = multiply by 1
• 25-30 litre = multiply by 1.5
• 40+ litre = multiply by 2

Temperature factor (daily average):

• <15°C = x 0.4 (under-water)
• 15-20°C = x 0.8
• 20-25°C = x 1.0
• 25-30°C = x 1.3

• 30°C = x 1.6 (sometimes twice daily)

Example: 20-litre pot, 24°C => base 600 mL, climate factor 1.2 = 720 mL today.

Honestly: use your finger. That is most reliable.

Special water needs by tomato variety

Some tomato varieties have different water needs than average.

Cherry tomatoes (Sungold, Black Cherry)

• Smaller fruit, less water loss
• Pot can be smaller: 12-15 litre
• Water: 400-600 mL per day
• Tolerate drought better

Beefsteak tomatoes (Beef Master, Brandywine)

• Large fruits, more water loss due to surface area
• Need larger pot: 20-25 litre
• Water: 800-1000 mL per day
• Prevent cracking: consistent watering (not dry-then-flooded)

Plum/paste tomatoes (Roma, San Marzano)

• Thick tissue, somewhat drought-tolerant
• Medium pot: 15-20 litre
• Water: 500-700 mL per day
• Tolerate a few dry days better

Golden/yellow varieties (Golden, Yellow Perfection)

• Thin tissue, prone to cracking
• Regular consistent water needed
• Water: 600-800 mL per day
• No fluctuations

Step-by-step

Step 1: Choose your pot size

Decide based on your situation:

• Can water daily? 15-20 litre works
• Cannot water every day? Go to 25-30 litre

Step 2: Fill the pot with moisture-rich soil

Use soil with compost, peat or coco (moisture-retaining). Dry potting soil dries too quickly.

Step 3: Check moisture: stick two fingers 2 cm deep

Feels dry: water now. Still feels moist: wait.

Step 4: Water in the morning

500-800 mL per day for normal 20L pot in summer. Adjust for temperature and plant symptoms.

Step 5: Repeat daily in June-August

Growth and fruiting require consistent moisture. Do not skip days.

Frequently asked questions

Can I bottom-water my tomato pot via self-watering system?

Yes, works well. Place your pot in a saucer with water, or use a drip line on a timer. Ideal if you go on vacation. Ensure drain in saucer stays open (prevent waterlogging). For August production, I recommend a true drip hose: even and no leaf wetting.

How do I know if my tomato needs more or less water?

Observe daily how your plant looks in the morning. Does the leaf wilt after watering? Too much water. Does the leaf not recover later in the morning? Too little. Ideal: slightly wilted mid-afternoon, fresh in the morning.

Can I water the leaves from above?

Better not. Water on leaves in evening increases fungal diseases (powdery mildew, septoria, phytophthora). Water at the root base, not over leaves. Morning spray (13:00+) is acceptable; it dries quickly.

What if my tomato gets no water for two days?

In May: no problem, plant survives easily. In August (hottest period): Plant wilts severely but usually recovers same day. Problem: repeated dry periods cause cracking (water stress). Ensure consistent watering.

Is rainwater better than tap water?

Rainwater is free and contains no chlorine. For a tomato pot, it makes little difference. Tap water is fine. Collect rain via a rain barrel for savings in hot summers.

Discover your own garden design

At [gardenworld.app](https://gardenworld.app) you can upload your front yard and see where vegetable pots fit best - considering shade, windbreaks, and accessibility for watering. Plan before you place pots!