Advice
August's weather
Sultry late summer
August is usually one of the hottest months of the year. It is often dry and sunny, but can be thundery, with summer storms. It can feel humid and dull. Pests and diseases thrive in such conditions. Lawns, hedges and weeds are generally growing more slowly in late summer.
Temperature
Nightly temperatures rarely drop below 11-13°C in the south of England, and 8-10°C in the north of England and Scotland.
During sunny days, temperatures can be double this or more, up to 35°C plus in some places. Cooler conditions are more likely on higher ground and by the coast. Inland flats and valleys can be the warmest areas during the day.
There is virtually no risk of frost anywhere in the UK, except in frost pockets on the highest mountain peaks.
In wetter, duller conditions, areas such as the north and east of Scotland can be cooler, with mean temperatures only reaching 14-15°C. But there should still be some warmer days, and night temperatures are still unlikely to fall below the 8°C mark.
Ventilation in the greenhouse and conservatory will be a priority, as will ensuring that fruit trees and border plants are not overcrowded. If the air can circulate around them, this will reduce the risk of fungal disease. Shading will also be necessary on sunny days. Remember to keep ponds and water features topped up.
Rain
The amount of rainfall varies considerably both from year to year, and depending on where you are in the UK. August 2003 saw an average of 27mm (1in) rainfall across the UK, whereas August 2004 saw 159.5mm (6.5in) on average. 50mm (2in) is a more common figure for the south east of England, and 90mm (3.75in) for the whole of Scotland. Regional variations within Scotland see the west and north being the typically rainiest regions. Within England, areas of higher ground and the Midlands are the most prone to thunderstorms. East Anglia, particularly the Essex and Suffolk borders, are classically dry areas.
Despite any bursts of heavy rain, watering is of paramount importance, as the downpours will mainly run off rather than penetrating to the water table. Water reserves will still be low, and plants will be using up more water than usual, because of the higher temperatures. Watering during the rain can actually be a smart move, as the rain will have wetted the soil surface, making absorption more efficient. Use grey recycled household water or stored rainwater wherever possible.
Dew can be heavy at this time of year, which helps limit drought stress, particularly to smaller shrubs, herbaceous and annual plantings.
Wind
Gales are uncommon in August, but strong winds are possible in coastal areas, particularly in the north and west of England, and in Scotland, particularly the western isles.
For most of the UK, conditions are generally still and close.
Ventilation of the greenhouse or conservatory will be a priority. Fruit trees and border plants will benefit from being pruned or thinned if overcrowded, as freely circulating air will help to reduce the risk of fungal disease.
Despite the still conditions, it is worth checking plant stakes and supports, as thunderstorms and heavy rain can be just as damaging as high winds.
Light
August is generally a bit duller than July, with increasingly marked differences in day length between the north and the south of the UK.
The south of England can still expect light levels in a broadly similar range as in July (175-180 hours over the whole month). Some areas will actually get more than this in a good year. Light levels over 200 hours have been recorded in particularly sunny summer months. Light levels are often lower in the north of England (150-160 hours over the month). Scotland receives the least light (about 140 hours in total on average).
This means that the growing season is beginning to wind down, even though temperatures are still warm. New sowings or cuttings may struggle, even with extra heat, and fertiliser and water requirements will be less than earlier in the summer.