Frost

To plant or not to plant, when is the question!
By Alan Titchmarsh

There was a time when the gardening novice could time the planting out of tender bedding by watching to see when the groundsman of their local park planted up massed displays in beds and containers. Now though, so few parks are planted with summer bedding that this expertise and foolproof guide to the local climatic conditions is lost. Tender plants, like summer bedding and patio plants, cannot cope with freezing temperatures and cold winds, so they must not be planted outside until after the last frost in your garden. Even after this date you should be prepared with sheets of newspaper or gardening fleece to hand so that you can protect vulnerable plants on cold nights. If at all unsure, I always advise to err on the side of caution and plant slightly late to avoid disaster.

Use the map, below, to help you work out when you are likely to expect your last frost of spring. Also keep tabs on the weather forecast, because the last frost dates can very dramatically from year to year. Make a point of checking out the Crocus three-day weather forecast as a guide. The altitude and exposure of your garden will also need to be taken into account. For example, for every 50m (150ft) above sea level the last likely frost date of spring can vary by as much as a week. Bear in mind, however, that cool air sinks so that the coldest areas are often at the bottom of valleys where the cold air is trapped (known as frost pockets). On a much smaller scale, obstacles such as fences and walls in a sloping garden can trap cold air behind them causing a localised frost pocket. For this reason, you need to understand the microclimate in your garden - it can vary even over very small distances. If you are new to gardening or have recently moved to a new garden, take the time to keep a record of which borders are first to get frosted as well as those which remain frost free even on very cold nights.

Hardening-off plants

Now that few gardeners raise their own plants from seeds and cuttings, the essential technique of hardening-off is fast becoming a lost art. All tender plants which have been grown inside, and even some hardy plants that have forced by growers for sale in garden centres in early spring, need to be carefully hardened off before being planted outside - unless the supplier has already done this for you. If you are not sure, you'll need to allow about two weeks to harden-off the plants yourself at this time of the year. The technique is easy enough, you simply wean the plants gradually from the cosy environment to which they have become accustomed, until they can cope with the harsher realities of life outside. If you have a coldframe or greenhouse this is easy to achieve, by gradually increasing the amount of ventilation to improve airflow and slowly reduce the temperature. At first, ventilate during the day only, slowly increasing the time and amount of ventilation during the first week until you can leave the coldframe open on milder nights. During the second week, ventilate freely during the day and shut at night only if cold temperatures are forecast.

If you don't have any of these facilities, you can harden-off plants perfectly well in a sheltered corner of your garden, once the last likely frost has passed. I often harden-off bedding under a hedge at the bottom of my garden when I've run out of space in my greenhouse and frames. Cover the plants with a couple of layers of gardening fleece overnight and during cold or windy conditions, removing it during the day if the weather is mild. As before, uncover the plants gradually over the following days until they are left completely unprotected on all but cold nights. If your garden is exposed to the wind then you will have to take extra care.

Other jobs for the weekend

  • Give grey-leaved shrubs a trim to keep them compact
  • Stake perennials that tend to flop in summer
  • Continue to prune early-flowering shrubs
  • Look out for self-sown seedlings that you can pot up and grow on
  • Lift and divide perennials
  • Protect vulnerable plants from attack by slugs and snails
  • Tie in whippy new growth on climbers
Check for winter damage and prune if necessary

Happy gardening!