Garden tips for May

Keep an eye on the weather this month. Sunny days can bring high temperatures but clear skies and possible frosts. If you have a greenhouse, consider fitting an autovent to keep the temperature down during the day. Always have some horticultural fleece to hand and group vulnerable plants together so you can cover them at night if necessary. Many half hardy plants can be hardening off now, ready for planting out, when there are no frosts where you live. When the ground is dry take the opportunity to hoe the borders and the vegetable patch to keep annual weeds in check; hairy bittercress and shepherd’s purse can reach epidemic proportions if you do not keep on top of them. Perennial weeds are in active growth now and can be treated carefully with a systemic herbicide; dandelions are often in full flower, deadead them before you treat them as they can often seed before they die. Early May is a good time to apply a dressing of fertiliser to the flower border. Avoid products with too much nitrogen as this can lead to floppy soft growth which will require staking later in the year. Give spring flowering bulbs a liquid feed to plump up the bulbs and ensure a good display next year. Deadhead narcissus and firm the soil around the leaves to prevent narcissus fly burrowing down to consume the bulbs. As you do this look for slug and snail damage and place out beer traps if you find any. If there are no slime trails and your plants are being eaten, slaters or earwigs are likely to be the culprits; inverted pots filled with straw on canes are a good trapping method. At the end of the month look out for lily beetles. They are not too common yet in Scotland but can make short work of lilies; as can the more common caterpillars of sawfly on gooseberry and related soft fruit. Mow the lawn on a regular schedule as it will be growing strongly now. Early May is a good time to lay turf and it is still not too late so sow grass seed, if you have patches to fill or need a new lawn. If it turns dry remember to water turf to stop shrinkage. Use a fine spray to stop the soil capping or the seed being washed away. Most of your herbaceous plants will be above ground by now. If you have gaps in your borders, sow hardy annuals such as calendula and nasturtium. Pots planted with dahlias, gladiolus or lilies can also be very useful for filling holes. In the vegetable garden, you can plant out new strawberry plants. Make repeat sowings of salad crops to ensure a continuous supply. Earth-up early potatoes to stop greening of the surface tuber. Plant brassicas but remember the pigeons will be watching so net them, or use fleece to avoid caterpillar damage too.