Advice
April's weather
Sunshine and showers
Spring should now be in evidence, with daffodils in flower and blossom adorning trees. But there are likely to be marked regional differences in the weather across the country. In Wales, the Midlands southeast and south central England, the seasonal averages are broadly similar. However, in northern England, the spring is about a week behind, and in Scotland it is two to four weeks behind, depending on the locality. On the Lizard and other especially mild southwest regions, spring is more advanced, and tasks can be carried out sooner than anywhere else in the UK.
Frequent sunny days and rising temperatures make perfect gardening weather. It is now possible to sow and plant most vegetables and flowers, and even to begin harvesting a few edible crops.
Temperature
With longer days and stronger sunshine, growing conditions are now improving rapidly. Average daytime temperatures for the UK as a whole are typically above 11°C (52°F), with regions varying by 4 or 5°C (6-8°F) around this mean. Maximum temperatures in Scotland generally hover around 10°C (50°F), whereas southern England maximum temperatures are about 12-14°C (54-57°F).
At night, temperatures across the UK average 3.8°C (39°F), generally varying between 2.5 and 4-5°C (36-41°F). Gardeners can still expect around four frosty nights over the month. In Scotland, there is twice as much chance of frost as in England, especially in eastern Scotland, which is colder than western Scotland at this time of year. Cornwall and south Devon very rarely have frost in April.
If a sudden cold spell is forecast, protect tender plants and new shoots with a double layer of horticultural fleece. Unfortunately, Magnolia flowers can often become browned, and Acer leaves scorched by April frosts.
Continue to check your conservatory and greenhouse heaters, to make sure they are working properly (a maximum-minimum thermometer is useful for monitoring). In many cases, one frost could kill an unprotected tender glasshouse plant.
Rain
Widespread bursts of rain, or ‘April showers’, are common this month. But do not be deceived by sudden bursts of rainfall. Ground water reserves are very low after a very dry winter, and showery rain will tend to run off or evaporate before it can penetrate the water table and replenish rivers and wells.
With overall UK averages of only 57mm (2in) of rain for the whole month, plus rising temperatures, the soil is drying out in all but the wettest and coldest areas. Northwest parts of the UK can still expect around 100mm (4in) of rain, but if you live in a dry region like East Anglia or southeast England you may need to start watering vulnerable plants such as seedbeds and new plantings during dry, bright and windy spells.
If you need to dry out your soil further before sowing seed outside, then you can speed up the natural drying process by about two weeks, by lightly cultivating the soil. Covering it with fleece, cloches, or plastic, will warm the ground, improving the germination of seed crops like carrots.
Heavy rain showers and melting snow, which are still common in some districts, will continue to wash nutrients out of the soil. These will need replacing by applying fertiliser.
Wind
Generally the wind eases off this month, but thunderstorms can bring short spells of gusty weather. North and north-westerly winds can still bring snow, but southerlies will bring warmer days with a hint of summer.
Light
The days are now much longer, with light levels averaging out at three quarters of the maximum summer levels. However, in northern districts, and when there is substantial cloud cover, light levels may be lower, and plant growth not as strong.
Most areas can expect around 150 hours of sunshine, ranging from about 120 hours in a dull year to about 190 hours in a sunny year.
Remember to ventilate the greenhouse or conservatory during the warmest part of the day, to prevent the sunshine scorching the leaves of your plants. Consider applying shade paint to the glasshouse panes, to protect them from the stronger sunshine at this time of year. Shade netting is an alternative, and newspaper is the cheapest option.