Gardening Monthly Calendar - May
Apr 30th 2018 ⋮ in Advice

What to do in your garden in May?

This month we should be seeing an increase in temperature with sunnier and drier days, meaning the lawn will need regular mowing. Sowing and planting out bedding can begin, but be mindful of late frosts.


If the weather is dry, it can help to retain moisture and nutrients by leaving grass clippings on the lawn after mowing. At this time of year mowing should be done at least once a fortnight and add clippings to the compost heap in layers.

Using a spade or a half-moon edging iron, create a 3 inch gutter around the edge of your lawn to help prevent grass from growing in to paths and borders.

Sowing new lawns and over dead patches can still be done in early May. Do not walk over newly sown grass until it has reached at least 3 inches and then only trim on a high setting. Ensure new lawns do not dry out.

Use a high nitrogen summer lawn fertiliser for a lush healthy lawn. Now is a great time to apply lawn weed killer to your lawn.  Always follow the instructions on the label of the product you are using.

During particularly hot weather your lawn may need watering, new lawns especially should not be allowed to dry out.


May is a great time to brighten up patios and doorways by planting up hanging baskets. Hanging baskets can be kept indoors or in a greenhouse until the weather is consistently warm. For best results, use a good quality compost with slow release fertiliser and water retaining crystals. This will help the baskets to last the full summer. Planting around the edge of the baskets can give the appearance of a fuller, brighter basket quicker and will fill out as the plants grow.

Summer bedding can be planted in to containers, when frost is no longer likely towards the end of the month. Cannas and Dahlias can also be planted out towards the end of the month. To grow your own spring bedding for next year, they can be sown from now until July.

After primroses have finished flowering, they can be divided and planted into a nursery bed until autumn, to display the following spring.

Spring bulbs will be fading now, so deadhead dying daffodils and tulips but leave the foliage to die back naturally.  For good flowering of spring bulbs next year, apply a liquid fertiliser after they’ve finished flowering.

Forget-me-nots can release a lot of seeds and become unmanageable, so lift clumps of the plant before too many seeds drop.

Herbaceous plants that have heavy flowers, such as peonies can benefit from being supported by a cane before they grow too tall.

To encourage new growth, trim back trailing plants such as Alyssum and Aubrieta which can become tired looking if left unkempt.

Trees and Shrubs

Check for any birds nests before trimming and hedges or bushes.

Evergreen hedges can be clipped at this time of year. Provided the waste isn’t overly woody, it can be shredded and added to your compost.

Clematis montana can be cut back quite heavily once it has finished flowering. Try to untangle the stems so you are able to see what you are trimming.

Tie in climbing roses to restrict sap flow, to cause shoots to grow along the side of the stem, so more flowers will be produced.

Prune pyracanthas that are wall-trained, trimming new growth by about 3 inches to increase flowering.

Pests and Disease

Pests will continue to be a problem during the mild weather up until the winter. Watch out for virburnum beetles that are most active between late April and June and can severely damage foliage, causing discolouration and holes to the leaves. Early prevention of pests and diseases is easier than curing.

Protect hostas, lilys and delphiniums from slugs and snails. The mild weather at this time of year can often see a rapid increase of aphids, caterpillars and other fly pests; early infestations can be removed by hand.

Check roses for any sign of black spot, black spot is easier to prevent than it is to treat. Watering the plant in the morning can help prevent the disease as it allows the water to evaporate, and avoid getting the foliage wet.


Vegetable seeds such as marrows, pumpkins and squashes can still be sown this month in to pots, keeping compost moist. These should be kept in the greenhouse until there is no risk of frost. In warmer periods, open vents and doors to release some heat. If the weather is particularly hot greenhouse shading can be used but this will reduce the amount of light that plants receive.

During hot spells, dampen the floor of the greenhouse to increase humidity and to help deter red spider mites.

Fly traps can be hung around the garden to help catch flying pests.

Young plants raised by seeds can benefit from being exposed to the outside gradually. Start by taking them outside during the warmest part of the day and gradually increase to over-night. Doing this for around 2 weeks before you plant them outside will increase their chances.


At this time of year annual and perennial weeds can rapidly increase, hoe borders to prevent weeds spreading and establishing roots.

Odd Jobs

Continue to earth up potatoes, depending on how big you want the tuber to be and what type of crop it is as to when they are ready to lift.

Keep containers and hanging baskets well-watered as the weather can be particularly dry. Use collected rain water or recycled water to water plants when possible as rain water has a neutral PH.

Any newly planted trees and shrubs need checking regularly so that they do not dry out.

Check that any tree ties are not becoming too tight and digging into the bark.
Climbers need regular tying to their supports in order to control where they grow.

Use a hard brush or a jet wash to remove dirt and algae from walls, paving and patios.