What to do in the garden in May

April on the whole has been warm and sunny, and at times positively hot!  There have also been the opposite extremes with frosts still being a regular feature of early mornings, and so it has been a confusing time for young plants.

The very warm days coupled with a regular watering routine means that everything seems to be growing rapidly; we can almost see some plants getting bigger in front of our eyes!  With luck we may be able to wave goodbye to the frosts soon, but we can never be really sure until the last week of May, so at the trials field in Kentford, we are still keeping tender flowers and vegetables under wraps for some of the time.  We are lucky enough to have been able to install a new polytunnel at the trials field which is a great addition to our trials team’s growing space and helps us keep young plants and seedlings warm through the frosty mornings.

So, what do you need to do in the garden in May?


Jobs in the flower garden in May

Canterbury Bell Seeds from Mr Fothergill'sSo as May begins, it is time to start the process of hardening-off half-hardy annuals and perennials ready for your summer displays.  All this means is gradually accustoming them to outside conditions before planting them out to their flowering positions later in the month.  To begin with, take them from the greenhouse or cold frame for a few hours a day, returning them at night and protecting them with fleece or newspaper if frost is forecast.  Then they can be left outside all day for a week or two, again returning them under cover at night, before leaving them out night and day for a week or so until they are acclimatised enough to be planted out.  They should then grow away with the minimum check to their systems.

Once the weather warms up a little more, half-hardy flowers destined for bedding schemes, borders, hanging baskets and other containers can begin to be ‘hardened off’ or become gradually accustomed to outside conditions before being set out to their flowering positions.  To begin with, take them out of the greenhouse on warm days and place them somewhere sheltered, returning them to the greenhouse at night.  After a week or so, start to leave them out overnight, as long as frost is not forecast, taking them back into the greenhouse if this is the case.

By the end of May they should be outside virtually all the time, although local conditions will vary around the UK.  Most half-hardies can be planted out in late May and early June to provide you with a wealth of colour right through the summer until the frosts return in the autumn.

sweet peasIf you have not already done so, plant out sweet peas either from an autumn sowing or ones made earlier this year.  They require the same support system of canes and netting or ‘wigwams’ as runner beans do and they are just as easy to grow, being naturally self-climbing and self-clinging.   They may, however, require a little encouragement in the earlier stages of growth, so be prepared to tie them in for the first few inches.  Keep a look-out for slugs around newly planted sweet peas, and keep them well watered at all stages of their growth.

If you fancy growing some really long stemmed and large flowered blooms, why not try growing a few plants as cordons?  This is really no more difficult than training indeterminate, greenhouse tomatoes.  Train just the strongest stem up a single cane, removing the weaker ones.  Remove tendrils and side-shoots as they appear and tie in the stem to the cane as it grows.  It’s a little harder work than growing them as ‘bushes’, but you may be impressed buy the quality of the blooms you produce.

Don’t forget we are holding our annual national sweet pea competition again at Capel Manor College, north London, on Saturday, 18 July.   It is open solely to ‘ordinary’ gardeners, plus classes for schools and individual youngsters.  There are big money prizes up for grabs, so growing sweet peas can be rewarding in more ways than one!  If you cannot make it to Capel Manor, we have a great way of making sure blooms reach us safely by post – all it takes is a two-litre soft drink bottle!  Full details of how to do it are here.

Helenium seeds from Mr Fothergill'sAs forget-me-nots finish flowering, you may wish to pull them up, as they self-seed very freely.  Alternatively, if you are happy to have ‘volunteer’ plants popping up throughout the garden to flower next spring, leave them a little while longer to let the ripe seed disperse before removing the spent plants. Looking ahead to next year’s forget-me-nots and other biennials, May is the ideal time to make sowings of these.  Wallflowers, Canterbury bells, foxgloves and Sweet Williams can all be sown now.  Sow in trays or in the open in a seed bed, although wallflower does much better if sown in a seed bed, as tray-grown plants do not thrive.  Plant them out to their flowering positions in the autumn and forget about them until they burst into life and flower next spring and early summer.

Have you heard of the ‘Chelsea chop’?  It’s less painful than it sounds and is a  technique used to promote better flowering in some perennials.  By cutting back border plants such as helenium, echinacea, solidago and a host of other perennials to about half their size, they will branch out, make bushier growth and produce more flowers than if you had left them to grow unchecked.  This procedure is best carried out with a pair of secateurs in late May, around the time of the Chelsea Flower Show, which serves as a timely reminder.

Spring-flowering species of clematis such as Clematis armandii, alpina and montana can be pruned back now that flowering has finished.

Once you have weeded round roses and perennials and the soil is damp, this is the perfect time to give the plants a 3-4in deep mulch of well rotted farmyard manure, home-made compost or composted bark.  This will help trap the moisture in the soil, suppress weed growth  and improve the structure of your soil as it is gradually taken down by worms.  We believe mulching is one of the most valuable actions you can do in the garden, but

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