Plants hate an irregular supply of water. Most of them, especially newly planted ones, need a constant supply of moist, but not soggy, growing conditions. With the increasingly erratic weather brought by climate change this is often challenging for gardeners.
How and when to water depends on the size of a plant. Established ones can tolerate arid spring weather that would kill young transplants. And plants grown in containers usually need more cosseting.
Water so that plants receive a regular supply and avoid erratic dousing followed by very little. Many plants struggle when the weather swings from one extreme to the other with heavy downpours following a long dry spell. Then plants which had merely survived respond by rushing headlong to flower and set seed, with skins cracking as a result of the sudden injection of water. And, of course, pests and diseases quickly suss out any struggling and poorly performing specimens.
When using a hose or watering can in the open ground, I always sweep slowly over the area several times rather than soaking a section once and then moving on to another part of the bed. This lets the soil gradually absorb moisture to a greater depth and prevents run-off. This also applies to pots and trays of seedlings. How often do you find most of the water runs through on to the ground leaving the compost still dry.
And it’s much easier to top up moisture levels than trying to rehydrate dry ground or compost: moist material readily accepts some more.
The volume of soil or compost also matters. A plot of ground takes in, and should retain, larger amounts of water and releases it more slowly, so less frequent watering is fine. This explains why we’re always advised to give ground a good soak rather than frequent sprinkles. But how often to ‘soak’ depends on the quality of the soil and the size of plants. Monitor whether you need to water by sticking your finger into the ground or pot. The top layer may have dried out, but the earth underneath, where the roots are, must be kept damp and never allowed to dry out.
But less frequent watering usually doesn’t apply with containers, especially small pots because there’s a much smaller volume of material and much less moisture to retain. And faster-growing, large-leafed fruit-bearers like tomatoes need liquid to cool themselves by evaporation as well as for growing. In a greenhouse, this could mean both morning and evening watering in high summer.
Soil or compost structure is always pivotal. When good, crumbly, and fertile, it absorbs and retains moisture both in containers and the open ground. When water passes through the pot, scarcely touching the roots, it means the structure has collapsed and you need to replace or refresh the compost with, at least a new layer on top. I find home-made compost or wormcast are always best and they help compensate for commercial material which often becomes inert and lifeless quite quickly.
Mulching helps to retain structure and moisture. Water passes through mulch more slowly and is completely absorbed without run-off. And the mulch prevents evaporation. In the open ground, a mulch stops weeds competing for precious moisture. Without a mulch, compost in pots would form a dry skin rather than providing nutrient for plants.
During a prolonged dry spell, re-arrange pots to minimise evaporation. When exposed to the heat from direct sun, the sides of pots readily dry out, but when grouped together, only the outer pots are affected.
And use plant saucers to reduce run-off. Properly watered large planters can then retain enough moisture.
Plant of the week
Iris “Jane Phillips” is a large, mid season bearded iris that has classic iris flowers in the blue of a summer sky. Also scented and rabbit resistant.