Train your plants to be less thirsty
Help your plants survive the drought, writes Gerry Daly, with a few easy tips
WITH all the talk of drought, it’s no harm to be aware of some preventive measures and strategies that you can use to help the plants in your garden survive. These strategies are built on an understanding of how plants use water and why.
Basically, water is part of the growth process, its hydrogen molecule combining with carbon dioxide to make carbohydrates. Just as carbs are the fuel for human consumption, they are the fuel that drives growth and keeps plants alive during the winter when growth is next to impossible. In fact, we humans actually eat the carbohydrates that plants lay down for winter use. As well as water’s importance in the growth process, plants also use it to cool down in hot weather, thus avoiding the likelihood of sun scald.
Outdoors, plants depend on natural rainfall but watering can be necessary if rainfall has been inadequate, or if a plant’s root system is not properly established. Seedlings, young plants, especially vegetables, and plants growing in shallow or dry soil, are the ones most at risk.
Watering is obviously necessary indoors
for house plants and for plants growing in a greenhouse or polytunnel.
There is a very simple way to assess whether the compost in a pot is adequately moist. Place a fingertip on the compost and press slightly. If the compost feels cold and wet, it is overwatered. If the compost feels dry and scratchy, then it is too dry. Ideally, the compost should feel moist and your fingertip should come away with a few crumbs of compost.
How much water do plants need? Normal summer rainfall is at least 50mm per month. This amount closely matches plant requirements. Twenty-five millimetres of rain is equivalent to almost 25 litres of water per square metre. If there has been no rain for a week, plants need about 12.5 litres per square metre — perhaps even more if the weather has been very hot. Established plants with deep roots can keep going in a spell of drought, but young plants may come under stress. 1 It is a waste of time, and of water resources, to water lawns because lawn areas recover so quickly, within a week or two, when normal rainfall resumes. 2 Lay down organic mulch. While mulches are best applied before the month of May to retain most moisture, they are still effective in late summer, especially if some watering is done to rescue a badly stressed plant. 3 Plants do not waste time making unnecessary roots. When new plants are set out, they need to grow fast to establish themselves in either pots or the open ground. If overwatered from the beginning, plants become dependent on hand watering and can wilt rapidly in the event that service not be kept up. 4 By observation, get to know which plants need watering and which ones don’t, or at least, which need less. For instance, among vegetables, peas and potatoes, lettuce and sweetcorn, French beans and rhubarb, all need relatively larger amounts of water.
Among ornamental plants, those from Australia, California and the Mediterranean hills such as lavender, rosemary, geranium, pelargonium, fuchsia, are likely to be able to survive, once established, on very little water. Think of grey-leaved or woolly-leaved plants that are sun lovers and have adapted by evolution to survive water shortages. 5 The combination of watering new plants that need it and ignoring those that don’t is the best way to make watering easy, less time-consuming and more effective. The key to good watering technique is to water at the base of the stem to make sure the water filters down deeply into the soil and, if you’ve just planted out, the pot-set shape.