How and When to Water a Vegetable Garden

The commonest mistake is watering too often, not too little.

More garden plants are killed by bad watering than by drought, and most of the damage is done by watering a little, often. Almost everything below follows from fixing that one habit.

Deep and infrequent beats little and often

A light daily sprinkle wets the top couple of centimetres and no further. Roots follow water, so they stay in that top layer, and a plant rooted in the top few centimetres is at the mercy of the first hot day you miss.

Water heavily and less often instead. Soak the bed properly, then leave it until the top few centimetres are dry again. Roots chase the water down, and a deep-rooted plant looks after itself through a hot week.

How to tell you have watered enough: push a finger in, or dig a small hole with a trowel. If it is damp a hand's depth down, that is enough. If it is dry two centimetres down, you have wet the surface and nothing else.

When to water

• Early morning is best. The plant fills up before the heat, and the leaves dry as the sun comes up, which matters for fungal disease.
• Evening is second best and better than not watering, though wet foliage overnight invites mildew and it is the reason evening watering gets a bad name.
• Midday is not the sin it is made out to be. Water does not scorch leaves through a lens effect, that is a myth. You simply lose more to evaporation. A wilting plant at noon should be watered at noon.

Where to put it

At the soil, not on the plant. Wet leaves spread disease and most of the water on foliage evaporates before it reaches a root.

• A wand or a can at the base is fine and gives you control.
• Drip line or soaker hose is the best return on effort in a vegetable garden, because it puts water exactly where it is wanted and loses almost none.
• Sprinklers waste most of what they throw and wet every leaf, so they belong on lawns rather than beds.
• A buried pot or bottle beside a thirsty plant delivers water straight to the root zone and is an old trick that still works.

Holding on to what you have put in

• Mulch is worth more than extra watering. A good layer cuts evaporation sharply and keeps the soil temperature steady.
• Organic matter holds water. Compost dug in improves both drainage and retention, which sounds contradictory and is not.
• Shade the soil, not the plant. Close spacing and mulch keep the ground cool.
• Windbreaks save water. A hot dry wind pulls more moisture out of a garden than the sun does.

Who needs more, and who needs less

• Seedlings and new transplants have almost no root system and need little and often until they take, which is the one time that rule applies.
• Anything in a pot needs far more than the same plant in the ground, sometimes daily in summer, because a container has no reserve.
• Leafy crops need steady moisture or they turn bitter and bolt.
• Fruiting crops want steady water while fruit swells, then less as it ripens. Late heavy watering splits tomatoes and dilutes melons.
• Established perennials and fruit trees need a deep soak occasionally rather than anything frequent.

Reading the plant

Wilting in the afternoon heat is normal and is not by itself a sign of thirst. Many large-leaved plants, squash especially, wilt at two and recover by six without any help. Judge in the morning: a plant still wilted at breakfast is genuinely short of water.

Yellowing lower leaves and soil that stays wet are signs of too much, not too little, and overwatering kills more container plants than drought does.

See also: Mulching, which cuts evaporation sharply.