Some species require lots of water, others very little – and it's your job to know how thirsty the plant you're dealing with is likely to be.
When planting a shrub or a tree, a good douse is essential. The new plant usually arrives in a small container, so you need to encourage healthy root growth quickly. Dig a hole slightly larger than the rootball and pour in a bucket of water, a handful of bone meal and maybe a sprinkling of Rootgrow for good root development. Keep giving the shrub a bucketful of water every week during summer.
Conserve water by mulching 60cm round the tree. Any vacant space in a shrubbery should be mulched, keeping grass at a distance since it absorbs water and nutrients at an alarming rate. I have three apple trees in grass bordering the kitchen garden. Each sits in an island of soil, covered with mulch. I've gone a step further by constructing willow hurdles to stop the hens hurling the mulch everywhere with their frantic scratching. The barriers also prevent the geese nibbling leaf buds in spring or sampling a Bramley come autumn. Soil beneath mulch stays moist longer, so keep it that way by sticking the hose or watering can underneath.
Some vegetables, such as potatoes, courgettes and strawberries, are notoriously thirsty. Massive tattie shaws act as umbrellas, keeping summer rain well away from the ground, so I lay a leaky hose along the row at planting time, but you could also stick a hose beneath the shaws every week. Leaky hoses are the best way to water thirsty crops but they are a fiddle to install. Courgettes are generous croppers and certainly benefit from a leaky hose because their huge leaves lose lots of water through transpiration. Strawberries are often overlooked. Given how many large, succulent fruits they bear in a short time, it's hardly surprising they need up to two litres of water a day.
Regardless of how wet the summer is, these vegetables need fairly constant watering. Celery and celeriac are just as thirsty and will become stringy and utterly unpalatable if kept dry. But there's enough bare ground round the plants to let you off the hook during a horrible summer.
Possibly the worst weather pattern is a dry spring followed by a wet summer – precisely what we endured for the past two years. It's tempting to water religiously for the first week or two after planting then let the plants look after themselves. They will start to suffer during a dry spell and will be badly stressed when this is followed by a soggy period – one when the rain even reaches potatoes. This irregular supply of water causes problems. Potatoes may develop hollow heart, a condition where the centre of tubers becomes hollow and is surrounded by black putrescence. Other vegetables, such as garlic and onions, may bolt. Having survived a dry, stressful spell, they rush to set seed as soon as it rains. These plants need a different weather pattern: a moist period while the bulbs are swelling, followed by a dry spell for ripening.
Irregular water supplies are certainly damaging but, depending on the species, too much or too little water is equally bad. Most herbaceous plants need a steady supply and can't resist pest or disease attack if stressed. Dry, struggling flowers and shrubs will readily succumb to powdery mildew. This fungus makes it look as if someone's painted the border white. You can prevent it by keeping the soil moist: mulch and water every week. Spray the leaves with liquid seaweed. Aphids cause much less damage when a plant is growing well and roses are much less prone to attack from black spot.
Even though you can apply a mulch to help keep the compost in a container moist, you can't stop the sun drying out the sides of a pot, especially a terracotta or wooden one. Obviously you need to compensate with more watering, but consider mixing water-retaining granules with the compost. A pot, particularly a plastic one, may also become too soggy. If so, remove the plant from the pot and wrap the rootball in kitchen towel to absorb the surplus water.
Excess water damages a few other plants too. In summer, tulip and crocus bulbs need to dry out, preferably in the baking sun, so the worst thing to do is to keep watering them. This applies to bearded irises and dahlias, which will rot if they become too soggy. Pulsatillas, sempervivums and anthemis thrive in hot, dry conditions, so they should be given sparing amounts of water.
In the same way, my favourite pelargoniums need very little water. Natives of South Africa, they love dry heat and the leaves can turn yellow if the plant is waterlogged. Pots should be raised off the ground to prevent any build up of stagnant water and, as a precaution, I grow some beneath the eaves of a shed. n
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