Watering New Plantings: How Much, How Often, and When to Stop

Why rain does less than you think

The Irish gardener's article of faith is that we never need to water. It is wrong more often than right, and wrong in exactly the case that matters — a plant that went in this year. Three things conspire. First, the rain shadow: a wall, a mature hedge or a tree canopy throws a dry zone behind it that stays dry through a wet week, and the strip along a south-facing house wall is the driest ground in most Irish gardens — also where people plant climbers. Second, our summer rain mostly arrives as showers, and a shower wets the leaves and the top 20mm of soil, while a new shrub's roots sit 200 to 400mm down. Third, a rootball of nursery compost in garden soil behaves like a sponge in a bucket of sand: water moves reluctantly between the two.

The soil can be wet and the plant still thirsty. That is the whole problem in a line.

How much, how often, and for how long

Water deeply and infrequently. A daily sprinkle wets the surface only, training roots to stay where the next dry spell will find them. A heavy soak once or twice a week drives water through the whole rootball, and roots follow water down.

• First season: a full soak once a week from April to September, twice a week in any dry spell of ten days or more. Newly planted evergreens need it in a dry March or October too.
• Second season: a soak every ten to fourteen days through the dry months. Reduced, not abandoned.
• From the third year: trees and shrubs in open ground can look after themselves, except in real drought or on free-draining ground.
• Autumn plantings need little over their first winter, but are still first-season plants the following June.

Hedging is the case most often missed. A whole hedge dries together, and a seep hose along the base left running for an hour beats a can working down the row.

Check with your hands, not your eyes

• Push a finger into the soil at the edge of the rootball; dry to a knuckle in summer means water.
• Better, open a slot 100 to 150mm deep against the rootball with a trowel and feel what comes out. Cool, dark and holding together when squeezed is fine; pale, warm and crumbly is not.
• Lift a container: weight is the most reliable test there is.
• Check before you water, every time, rather than watering to a timetable.

Do this a dozen times over one summer and your eye learns what a dry week looks like on your own soil.

Making the water land where it matters

• Leave a shallow saucer around the plant at planting, or build a low ring of soil 300mm out from the stem to hold a fill of water while it soaks in.
• Fill it, let it drain, fill again. Two slow fills beat one fast one.
• Aim at the rootball and just beyond, not at the leaves or the mulch.
• Water in the evening or early morning; midday water on a bright day mostly evaporates.
• Mulch after watering, never before.

Containers are another regime entirely

A pot is a different climate: no reservoir, no capillary rise from below, and terracotta losing water through its walls. In summer, containers may need water daily and large pots in wind twice daily. Water until it runs freely from the base, then stop; never leave a pot in a full saucer, as roots in stagnant water rot within days. Do not assume rain has done the job; a leafy plant acts as an umbrella and can leave its own compost bone dry after a wet afternoon.

Too wet or too dry — they look the same

Both give a wilting, yellowing, miserable plant, and gardeners reliably respond by watering more.

• Drought: leaves wilt in the afternoon and recover overnight, edges brown and crisp, older leaves dropping first, the rootball light and pulling away from the soil.
• Overwatering: leaves wilt and stay wilted overnight, yellowing starts low down, foliage soft rather than crisp, the soil sour-smelling, often with liverwort at the surface.
• The test that separates them: open the ground beside the rootball with a trowel and feel it. Ten seconds, never ambiguous.

Some plants warn you first. Hydrangea macrophylla collapses dramatically and recovers within an hour of a soak. Acer palmatum scorches at the leaf margins. Astilbe and Ligularia flag before anything else in a border. Newly planted Betula and Prunus laurocerasus shed leaves without drama, which is why they are so often lost quietly.