What to do in the Garden in May

The Sunday Gardener's Calendar for May is full as May is such a busy month in the garden.  

 By May, Spring is in full swing, but the weather can still catch us out with unpredictable changes from mild spells to a shift down in temperatures and chilly winds. The gardening magazines may be in full Spring glory, but are the gardens? All gardening advice needs to be adjusted to the weather, and each Spring brings different weather from the previous year. In many parts of the country May is a month in which more tender plants can be put outside, but not in the northern parts and it depends on the May weather. We should be frost free by the end of May, but it is always an idea to have a fleece or cloche handy. 

May is a good time to think about the "Chelsea Chop" which is a great way of stopping some plants getting too big and leggy, and with others, staggering flowering times. The plant needs to be of a reasonable size and it is important not to chop too early in May if plants have just not reached the right growing stage because of a cold spring. If you haven't used the Chelsea Chop before it is really worth considering; for more tips and information about the Chelsea Chop. Video :How and when to do the Chelsea Chop

What to plant in May

May is a busy planting time in the gardening year. We gardeners are keen to get planting but we need to keep an eye on the weather - so what can we plant in May?

Plant outside now

  In the veg plot: Broad beansRunner beansPeasOnionsGarlicCarrotssalad crops,  LeeksStrawberries.

In the garden : all hardy perennials & evergreens. These are plants you may buy from the garden centre or on line which are described as hardy.  In terms of annuals you can plant out Sweet peas and Sow hardy annuals where they are to flower (explanation "hardy")

Delay planting outside

  Even in May the weather can still be cold and some plants are best to plant under glass and / or delay planting out at the end of month or Early June. These are the more tender vegetables which are : French Beans, Squashes, CucumbersTomatoes, Melon, Chillies, Aubergine Sweetcorn, Courgettes and Sweet peppers.

May is tomato time!  It's a good time to buy plants to grow on in the greenhouse, or late in May when all risk of frost has passed tomatoes can be planted out in the veg plot in a sunny spot. Tomatoes need attention to produce a good crop. Advice Growing tomatoes is set out  on the growing Tomatoes pages. There is also a handy Sunday Gardener E book " Success with Tomatoes" which contains  55 pages of detailed advice with 23 illustrations and approximately 12,000 words. (see below) 

By the very end of May/early June everywhere in the country is usually frost free and so it is safe to plant out tender Bedding plants, and non hardy plants such as Agapanthus (some), Canna Lilly, Dahlias.

A job for May, whatever the weather, is to stake perennials. I always leave this task too late and end up trying to persuade the delicate stems of a Peony through the hoops of a plant support. If you planted Dahlias earlier in the year, the growth takes about 6 weeks to reach to soil surface, which can be around May time so if there is a frost it will need to be protected. For advice and tips on growing Dahlias

May in the Flower Garden

   The Chelsea Chop 

Not like the Barnsley chop. The Chelsea Chop is a way of stopping back herbaceous and perennials plants to make them bushier, and flower slightly later. It's very good for plants which tends to get leggy later in the year, by chopping it in May growth will be checked, and the plant will throw out more shoots and flower later. This makes it less leggy and more bushy. The Chelsea chop is really a light prune and the result is a more compact plant which will flower slightly later.

Traditionally executed in Late May, (about or after the time of the Chelsea flower show after which it is named,) the idea is to prune the plant back by about a third, which means reducing the plant stems. You can either chop the whole plant, or selected plants in the group or individual stems on the plant cut back to stagger flowering. Experiment to vary flowering times and to make plants more bushy. Whilst May is traditional, it depends on the growing season as the plant needs to have put on a good degree of growth to be reduced by the Chop.

More information about the Chelsea Chop, details of suitable plants and a video. I grow Nepeta as Lavender struggles to grow well in my garden which tends to be wet, especially over winter which Lavender hates. Later in the growing season Nepeta sprawls all over the place, refuses to be contained by plant supports and lies on adjacent plants. The way to tame it and other plants which you wish were smaller and neater, is to use the Chelsea Chop; its very effective. The down side of Chelsea Chop is later flowers, and sometimes smaller.

Looking after Garden plants

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.  

  Growing Sweet Peas

April and May is time to plant out sweet peas. They are half hardy but it is still essential to ensure they are hardened off before planting out. Sweet peas look just great in the border climbing up an obelisk or suitable support and add colour, height and best of all scent. Sweet peas are an effort, but very long flowering with regular dead heading I have picked Sweet peas in late October so you do get your money's worth.  Sweet peas like moisture and one tip is to line the trench with newspaper to add extra moisture retention. If sweet peas get too dry they are prone to mildew. 

  For tips on growing sweet peas and for a video about planting out sweet peas. Sweet peas are marked as a red wheelbarrow plant, because they require time and effort throughout the growing season but reward with masses of blooms and scent. Sweet peas make a lovely cut flower and to look good in a vase we want them with long straight stems - tips on how to get straight stems on sweet peas.  

  Train Climbing plants

Climbing plants will be putting on spurts of growth in the warmer weather and need checking and the new growth to be tied in. This supports the plant but also enables you to guide the plant to grow where you want it to and not where it may want to go. It is a wild generalisation, but many climbing plants can be a bit of a thug, fast growing and clinging to anything around including neighbouring plants. It is good to train the climbing plants and tie it in otherwise you can find a smaller plant next to the climber gets tangled up and it's growth restricted by shoots from the climber.

Shrubs to Prune in May 

May is the time you can, if the shrub needs it, prune early spring flowering shrubs. These shrubs are pruned only after flowering, so whatever the books and magazines say with regard to the time to prune, it depends whether your shrub has finished flowering. Pruning helps to stop the shrub getting too big for it's space and to shape it. If you been admiring a spring flowering shrub, but at the same time thinking its getting too big, now is the time to attack. Cut back all of the older, woodier stems from the base, and if needed you can also cut back, by about half, any long stems. Suitable shrubs are Deutzia, Ribes sanguineum (Flowering current) ForsythiaPhiladelphus (mock Orange) Spiraea arguta and Viburnum bodnantense. Some of this group maybe ready for pruning in May such as the Forsythia others may need to wait until June.

  Annuals

There is still plenty of time to sow annuals to add to the colour of the borders and many are very easy to grow. The advantage of sowing annuals is that you can pick from a wide range of seed and grow plants you do not generally see in the garden centre. Some annuals are showy but not easy to grow such as Cobaea Scandens. It is very tender, a native to South America and a beautiful climbing plant to have as part of the summer display. It's common name is the cup and saucer plant which describes the flower shape. The specialist seed catalogues have a fantastic range of seeds and its great fun to grow something unusual.

Another excellent annual is morning glory Latin name Ipomoea . Again, a very tender annual and it is best grown on under glass until at least early June before planting out.   An easier annual which is attractive to bees and butterflies is our native Cornflower Centaurea cyanus, image above, and in its true blue colour can look stunning on its own or as part of a wild flower patch. Why not grow a collection of annuals and plant a wildflower patch. This a really easy way create colour and its much easier that you may think by using a pre seeded mat.  

  The vexed subject of planting out Bedding plants

Late May is generally a safe time to plant out bedding plants, but don't rush. If it's a cold May the bedding will not like it and planting out when it is cold can cause the plants to sulk. The plants we buy from garden centres and Internet providers have been grown in perfect conditions, warm, no wind or cold and perfect amounts of water. To bring these plants home and stick them outside in a cold May with a chill wind will give the plants a shock and set back growing. It could delay the plant's growth and flowering for a number of weeks. It is always better to plant bedding plants during a warm spell and get them off to a good start.

  Even if the plant is fully hardy, it is essential to " harden off" plants grown under glass so they are ready to be planted outside. Also plants purchased on line and in garden centres will have been grown in ideal conditions and need hardening off before planting out side in variable weather conditions. To do this, put the plants outside on milder days and nights, gradually exposing them to more and more time in the outside conditions. On colder days and nights, bring back under glass or cover with a fleece gradually reducing the cover until they are out 24/7 and acclimatised to the growing conditions outside. A good tip, if you have a potting shed or greenhouse, is to plant up the containers and grow them on in the greenhouse until late May. The plants will get established in the container and will be more mature when moved outside. Whether outside or in, nip out the growing points to produce a bushier plant otherwise some plants, particularly petunia, fuchsia, verbena will grow leggy, see image above. Whether growing bedding plants on inside/windowsills/in the greenhouse I usually stop them from flowering by pinching out the flowers until ready for planting out. There is no point in the plant using energy to flower in the greenhouse, nip out the flower and divert the energy to the plant growth until outside in the garden. Cut back early flowering Perennials This is the time to cut back early flowering plants. In May/June, the early perennials such as Aubrieta, and Alyssum have finished flowering and can be cut back. This promotes good flowering next year and encourages the compact shape. Simply trim into neat shape removing all spent flowers.

May in the Veg plot

  Growing Potatoes in May 

If you are growing potatoes outside keep an eye on the top growth, because if there is a frost, the top growth, called 'haulm', will need protection. This is illustrated left, and it can be damage by frost. If the top growth does get caught in a frost, the Potato will survive, although it is likely to delay the flowering and harvest. 

 Potatoes like to be planted into a warm soil, so check the soil, not the calendar, if you want to get them off to a good start. 

  The same applies if you are growing potatoes in containers. Check the temperature of the compost as bags which have been stored outside can be surprisingly cold. Cover the bed or tubs with fleece if there is frost. The early potatoes may need earthing up for the first time in late May/early June, which helps to improve the crop as it allows more potatoes to form as the season goes on; more about growing potatoes with tips and hints on how to get the best crop.  

   Vegetables to sow in May 

Continue to sow under glass the more tender vegetables such as French beans, tomatoes, sweetcorn, squashes, Cucumber and courgettes. These will need to be grown on under glass until frost free conditions are available in the veg plot which means late May/early June, depending on where you are in the country and the garden aspect. Delay planting out any of these veg until frost has passed

Onions and garlic can be safely planted out; advice on how to grow onions and garlic.


  If conditions are right and the soil warmed up, you can sow outside the hardier veg such as carrots, broad beansonionsgarlic and purple sprouting broccoli. Carrots always benefit from protection against carrot fly and this needs to be a physical barrier such as euro mesh, illustrated in the image above. Carrot fly can severely damage the crop, and although it is a nuisance to erect mesh around the carrots, it is the only safe way. Specialist varieties of Carrots such as Flyaway are less vulnerable to damage, but not guaranteed. Tips on how to grow carrots and a Video on how to plant out beans and Video on how to Grow and plant onions and garlic. Tomato plants which are filling their pots and beginning to look at bit top heavy will need to be potted on before being planted in final position/container. More about growing tomatoes and video How (and why) to Pot on tomatoes. Even at this early stage tomatoes will be producing side shoots and it is important to remove these regularly. Advice on side shoots look like and how to remove them on growing tomatoes and video. E book "Success with Tomatoes" by the Sunday Gardener, comprehensive guide to growing tomatoes.

  Herbs and Salad Crops

Herbs make a great addition to the veg plot, but not all herbs can be planted out just yet. 

Plant outside Thyme, Rosemary, Parsley and Mint. Sow the tender herbs, basil, coriander, dill, Thai basil, and tarragon in pots under glass ready to plant out later month.

Parsley can be slow to germinate, and may look as if its doing nothing, but don't abandon the pot for a number of weeks. Herbs are so expensive to buy they are always top of my list. Growing herbs from seed or small plants and home grown seem to last a lot longer than the supermarket versions.

  Tip re cycle supermarket herbs. I keep pots of herbs purchased from the supermarket over the winter and put them in the greenhouse. They re grow and get planted outside in the summer. This month is the right time to plant out lettuce and rocket, either as small plants or sow under a cloche. 

As the lettuce appear, so will the slugs. Slugs love young lettuce and will munch through a crop over night. More information on protection and how to beat the slugs

  Avoid gluts successive sowing

Even at this early stage in the growing season it is worth thinking about how to avoid gluts which is by "Successive sowing" To have a regular supply of veg it is necessary to sow/or plant a regular supply of plants or seeds at regular intervals so that they are ready to harvest spaced by the of planting interval. Generally seeds sown together, will crop together, and so create a glut. A useful rule of thumb, (and easy to remember) is to plant or sow every fortnight for successive cropping.

  Also in May check out emerging fruit on the strawberries before the birds do. Net and protect the plants from the birds to make sure you can enjoy the crop as the birds love strawberries. It is a good idea to place straw around to protect the fruit from dirt and rain splashes (which can cause mold). I like to keep strawberries covered with a cloche through the early growing months as the extra shelter aids an earlier crop. 

These strawberries are mulched with strulch a brand of mulch which I find very effective and easy to use. I use it on the strawberry plants and all around the garden as an good mulch. It is also very light and clean to handle.

Home