The recent heat wave put gardeners with their hose pipes and watering cans on high alert! Unlike people, plants can't move themselves to shady spots or turn the tap on for a cooling glass of water; they have to grin and bear it, until refreshing relief comes along. In the garden, varying water requirements by so many different types of plants growing in a variety of soils makes it a challenge for plant and gardener alike.
Plants use roots to take water and nutrients from the soil; a somewhat complex plumbing system carries the water and diluted nutrients all around a plant. Plants lose water easily from small holes (stomata) in their leaves; plants are clever and can control how much water they lose by closing the holes at certain times during the day. This does pose a problem for plants because these same holes are the pathway in for carbon dioxide, which is vital when they are making food during the photosynthesis process.
Plants know exactly how to balance the complexities of water economy and food manufacture. Visually when plants have enough water they appear rigid and firm, but once water becomes in short supply they wilt.
When the weather is hot and dry one of the first parts of the garden to be affected is the lawn, where thousands of grass plants with shallow root systems are in competition with one another searching for every last drop of water to survive.
While it's not impossible to keep the lawn green by watering in dry weather, it can be hard work and often overlooked because there are other areas that are in greater need of water. Incredibly, some species of grass, although they quickly turn brown, are resilient to dry weather, with only the finer species permanently dying away. After a reasonable amount of rain much of the grass will recover and soon 'green up', after which a liquid lawn feed could be applied to give the grass a boost. There may be areas of the lawn where the fine grasses once lived that look a little thin. Over sow with new grass seed in the autumn or early next spring to bulk it up and make less space for weeds to take hold.
Where I live, I am surrounded by a number of huge mature trees, which are looking green and healthy and haven't suffered at all during the hot weather. That's quite surprising given the daily amount of water that mature trees require.
On a hot sunny day a large oak would consume over 150 litres of water an hour and probably require 10 times the amount to survive the day; over a week or so that's a huge amount of water! How do they cope? Mature trees have massive root systems which delve deep into the soil and beyond to search out a necessary constant supply of water – a supply replaced indirectly by heavy rainfall during the winter months and most certainly by last year's seemingly constant excessive rainfall.
Every garden has soil which, for the gardener, is full of hope and potential. It contains organic material called 'humus' and inorganic particles of rock which together hold water, air, and supports a population of animals and plants.
A clay soil is heavy to dig because it contains fine particles and is full of water; it sounds silly but not all of that water is available to plants. The water in the spaces between the soil particles is available but water contained in the very thin film that covers each particle is not, so it stays stuck in the soil and useless to plants. Hot weather bakes a clay soil hard. Vitax Clay Breaker garden compost and manure applied during the autumn will help to improve the structure.
Plants such as roses, weigela, hypericum, forsythia and deutzia are happy growing in clay soil.
By contrast, a sandy soil is completely the opposite. Water moves freely between larger or rounded particles. This causes water and nutrients to drain quickly from the soil. The soil maybe easier and lighter to work but it dries out and becomes devoid of nutrients all too quickly. Well rotted manures and garden compost are good for sandy soils as they help bind particles together and improve water and nutrient retention.
Plants such as lavender, santolina, lampranthus, sedum, and brachyglottis (senecio) prefer well-drained soil and sun.
Gardeners who strive to have a good mixture of particles and organic material in their soil create good loam which is able to support a variety of plants through the typical mix of British weather.
Understanding the type of soil you have will help to answer the familiar questions; how often to water and how much water to apply? I have heard many a time how gardeners water their gardens every night, which may not be the answer. Let me put it another way and, at the risk of contradicting myself, please bear with me; if plants were meant to be watered every night it would be raining much of the time, and we all know how we feel about that.
Although I jest, there is a serious side. If garden plants need watering it is far more beneficial for them to have a really good soaking two or three times a week than to be on the receiving end of a light watering every night. By giving them a good soaking it forces their roots to go down searching for water. If the water is only available on the surface, the roots are encouraged to grow upwards towards the surface where they are likely to be damaged and scorched by the sun.
Plants growing in a greenhouse or conservatory, or any covered area are different; likewise hanging baskets and planted pots and containers. They will need checking daily sometimes twice and they may need watering both times. It's surprising how much water tomato and cucumber plants need once they are carrying a full load.
Young and shallow rooted plants. or plants that have recently been planted in the garden will all need water during dry periods. Roots of established plants are deeper and growing where the soil will be cooler and damp. Their need for watering will be reduced to once a week or fortnight or even less. Unbelievable though it may sound it is possible to give plants too much water during hot weather. Established plants do have ways and means of dealing with hot spells. After all, who looks after them when they are growing in the wild? I'll leave you to work that one out.
Plant expert Rose Clark has worked at Otter Nurseries, the region's leading garden centre chain, for more than 30 years. To find your nearest branch, visit www.otternurseries.co.uk or call 01404 815815.