May Annuals and biennials

For a succession of blooms throughout the summer months continue to sow the seeds of annuals such as calendulas, candytuft, clarkias and godetias every two weeks till the middle of June. In cold areas, however, complete sowing by the end of the first week of May as even quick-maturing annuals may not have sufficient growing time to flower well if sown later in the month.

Although at this time of the year hardy annuals will germinate if sown directly into seed beds outdoors, you will usually get better results by sowing them under glass and then pricking them out into pots or divided seed trays. You will then need to harden off the seed trays. If you adopt this method, strong, weather-resistant plants should result. Moreover there is no need for thinning and the root disturbance when planting out is minimal.

Annuals for late flowering include ageratums, love-lies-bleeding or tassel flowers, nicotianas, nasturtiums, zinnias, annual lavateras such as ‘Silver cup’ or ‘Mont Blanc’, ten week stocks and annual rudbeckias. If sown now, these annuals will flower from August until the first frosts arrive. They make the perfect gap filers for the mixed border, especially as they come into flower as many early flowering herbaceous perennials are over. Sow some in containers; these can then be moved around the garden to create interest.

Transplanting overwintered annuals

Move any hardy annuals, which are sown in rows and overwintered, to their final flowering position in the garden.

Feeding young plants

There is only a certain amount of fertiliser in compost and, when it runs out, seedlings and young plants can show signs of starvation. Such signs include poor growth, pale, yellowing foliage and red and purple leaf tints. This is a particular problem for plants sown early in the year which cannot be planted outside until the risk of frost has passed. Water them with a balanced liquid feed, applied according to the manufacturers instructions.

Clearing spring bedding

Once displays of spring flowers start to fade, or if you need the space for planting out summer bedding, you can begin to clear the beds. Most plants can be discarded, but bulbs, such as tulips, should be moved to a trench in a spare part of the garden to finish building up reserves for next year’s flowering.

Planting out

Check on the last likely frost date for your area. In milder regions it should be possible to plant out half-hardy plants around the end of the month. Plants sown during February or March should now be ready to harden off. Do this two weeks before you intend planting them out. Hardy annuals sown in pots and trays during March and early April can also be planted outside in their flowering position once they are hardened off.

Sowing biennials

In mild areas, towards the end of the month, you can start to sow biennials for flowering next spring. Sow the seeds in straight rows in prepared seed beds. Space the seeds out well to cut down on the need for thinning. Sow double daisies, forget-me-nots, polyanthus, wallflowers and sweet williams now, but leave Brompton stocks till June or July.

Thinning out

It is very difficult to sow hardy annuals sparsely enough to avoid overcrowding. Thinning may seem wasteful, but it is better to thin out plants than to keep seedlings crowded together. Overcrowded seedlings will grow tall and leggy instead of developing into bushy, weather-resitant plants.

Pinch out the tips of annuals, such as salvias, which can be induced into a bushy habit.

This will delay flowering but produce better plants.

Controlling pests

Plants are often infested soon after being planted out and, if unchecked, foliage and flowers can become unsightly. Watch particularly for aphids such as greenfly.