How to recognise it
The first symptoms of drought tend to be a dulling of the leaves and a general wilting of the plant. The leaves and roots will then dry and begin to brown. If the drought continues the leaves will start to drop and the plant will die, possibly going to seed first.
In tomatoes and peppers symptoms of drought are often first noticed as an appearance of blossom end rot, which is caused by a lack of calcium. The plant can only draw calcium up from the soil if it is carried in water, therefore without water the plant won’t get any calcium.
What causes it
Drought can be caused either by a lack of water in the soil (or potting compost) or by high and/or warm winds which can carry ‘pull’ moisture away from the plant quicker than it can be replaced from the soil.
Why it’s a problem
When a plant loses more water through its leaves than it can draw up through its roots it begins to wilt. It closes the ‘stomata‘ openings in the leaves which allow water to leave the plant and carbon dioxide to enter. This means that the plant is lacking both water and carbon dioxide, two main ingredients for photosynthesis, without which the plant can’t produce the energy required to keep growing. Unless the situation is rectified the plant will exhaust its internal resources and gradually die.
The speed at, and extent to which, drought affects plants will vary dramatically between different plants. As a generalisation, plants with large, smooth leaves will suffer most as they lose water rapidly from their leaf surface. Plants modified for drier conditions, such as cacti, will withstand significant shortages of water, but even they cannot carry on indefinitely without water.
Where you are likely to find it
Drought is most likely to occur in dry seasons and when there is a warm and/or harsh wind which can strip moisture from plants. It’s naturally more prevalent in well draining soils and with plants grown in containers or grow bags.
Any plant can suffer from drought, but those with larger, lush, smooth leaves are likely to be more vulnerable. Plants which originate from warmer environments, such as Mediterranean plants, will cope better with drought; look for plants which enjoy well drained soil and full sun. However, if you have cold, wet winters you may find that these plants suffer and need to be brought under cover or given winter protection.
How to prevent it
Make sure that you understand both your plant’s water requirements and the environment you are placing it in. Putting plants in soil which drains freely, in containers, in open/windy areas where humidity will be low or in places with high temperatures (such as glasshouses) will naturally make drought conditions more likely. This will give you a bigger watering job unless you choose plants which can cope with the dry.
One solution is to use drought tolerant, warmer climate plants. Plant them in the spring, as soon as the soil starts to warm up, to help them to establish over the summer and give them a better change of surviving the winter than they would have if planted in the summer or autumn.
In dry periods ensure that your plants are sufficiently and regularly watered (but not excessively so), particularly when they are flowering and fruit is setting. Give newly planted plants or plants growing in containers or grow bags extra attention, as they may need watering two or three times a day in very dry conditions.
Using a mulch will help to retain soil moisture and has plenty of other benefits, such as suppressing weeds and giving containers and borders an attractive appearance.
Try to avoid adding fertilisers to the soil in dry conditions; you may create an imbalance of water and minerals in the soil (ie too many minerals from the fertiliser to be carried by the water) which can prevent the plant drawing up the fertilisers and the water. In fact you could trigger plasmolysis, where water actually leaves the plant to balance up the ratio of minerals to water in the soil.
Wet the floor in glasshouses to maintain humidity, so there is less water loss through the leaves, and spray plants such as tomatoes, cucumbers and vines with water when they are flowering to aid pollination.
Growing plants, particularly those in containers, close together can help to maintain a level of humidity around them and reduce the levels of water lost through the leaves. Various water retention solutions for containers are also available to help to reduce the amount of watering trips you need to make.
If you need to move established plants, be cautious about where you move them to as, if they are used to a moist environment, they may fail to adapt to a drier environment. If you want to put plants into a dry soil, do so when they are small so they establish in that environment.
How to get rid of it
Act quickly at the first signs of drought to replenish the water supply; if you leave it too late the roots will start to desiccate and will be unable to draw up any water you do give them.
Lawns are generally pretty drought tolerant; even if they seem to be browning in a dry period they will generally recover fully once the rain has returned. You should only need to water lawns when you have had an exceptionally long period without significant rainfall.
Is it good for anything?!
Some consider a bit of garden drought a small price to pay for hot and sunny weather!
Other useful information
It’s a great idea to store rain water in wetter seasons to use to water plants when the weather dries up. This is not only environmentally friendly but also means that you are supplying your plants with a more natural water supply, rather than the chemically treated water that come out of our taps.