May it is a good time to feed plants. If you are growing plants in containers, especially tender plants which have been overwintered, this is a good time to feed them. You can do this without re-potting by sprinkling the fertiliser on the surface and gently, with small hand rake, work it into the top spoil. This is suitable for plants such as Agapanthus where the container maybe full with little bare soil showing.
Alternatively, if there is bare soil and room in the pot, you can "top dress" the container. This means to remove the top few centimetres of compost and replace with new compost with added fertiliser. Feed garden shrubs and roses now, just add a handful of fertile around the base of shrub and fork it in. If you have time, Roses benefit from at least two feeds per summer.
May is also the right time to stake perennials. Staking plans has a number purposes: it supports stems so that they are protected from damage, especially wind damage, it enables you to train them stopping them from flopping over and it keeps them upright so they do not lie over or swamp neighbouring plants. Some of the more vigorous perennials can grow over their neighbouring plants and smother them. Staking helps to keep them in order but it is important to get the stakes in place early. Staking and putting supports around plants, particularly the herbaceous perennials, helps them to look their best when in full bloom later in the year but it becomes more and more difficult to insert the stake as the plant puts on more leaf. If the plant is more mature, it is tricky to get the support in place without damaging plants or the budding flower heads. It is so easy to leave this job until too late. Many plants need support, for example Peony, Delphinium, dahlias, Allium, anything waving around in the wind looking vulnerable, or with heavy plant heads, such as Peony, and Oriental Poppies. The choice of support depends on the type of plant, but make sure any ties used are soft and there is room for the plant to grow. The Peony in the image left is just at the right stage to stake it before it has really put on much growth. The support is in place and the plant can then be trained through it. Different plants need different types of support; Peony do well with a grid support as in the image, Delphinium are better suited to individual stakes and plants such as Crocosmia respond best to firm supports to keep the plant upright, with string or raffia linking the supports.