Things to do in your garden in May.
Taken from the Ontario Master Gardener Calendar
By John Hethrington, Master Gardener Emeritus
Past President, Master Gardeners of Ontario
Please contact John for more information!
Garden Tips: Things to do in, or for your garden in May 2026!
- It’s been a long hard winter and a slow-to-arrive spring, with constant rain, recuring snow and lots of cold temperatures. Wiarton Willy must have died of embarrassment for forecasting an early spring this year!
- Find out your average last frost date (May 11 in Thornbury) and allow at least an additional 2 weeks (May 25th) before you plant out tender transplants and warm weather seeds, e.g. beans and corn.
- For my money (and yours) June 1st is the earliest to put out tender annuals and perennials.
- If you are growing seedlings, don’t forget to harden them off before transplanting them into your garden. Put them out during the day and bring them in at night or at least cover them with a bed sheet at night.
- Consider protective measures against slugs, cutworms, earwigs and tent caterpillars.
- Your Hybrid Tea roses should already be pruned back to 6” to 8” and any dead ends removed from other roses, like the climbers.
- Treat roses against black spot and aphids as required
- IMPORTANT! Take notes, and more importantly, take photos of your bulb plantings in bloom as a guide for possible changes and additions next fall.
- Deadhead faded tulips and daffodil blooms. But leave the green leaves to wither and die so they can charge up the bulbs for more blooms next spring. Being too neat and tidy can be a problem.
- If not done already, fertilize lawns with slow-release lawn fertilizer. Look for a high nitrogen number (the first number of the 3 on the bag). The extra cost is well worth it!
- Treat lawns against weeds and grubs as required.
- When they have dried up a little, start regular hoeing and hand-weeding your garden beds.
- Add well rotted manure around each perennial. It will improve the friability (look it up) of your soil and feed the plants all summer long.
- Having cleaned out the old leaves and cut back the tall plants, I sprinkle a little well-rotted manure around each plant in the garden. (I know it’s quite a job!) Then I gently dig the manure into the soil around each plant. You will be greatly rewarded for this extra effort.
- Mulch newly-planted seedlings and shrubs, plus add 2’ to 3” of mulch on bare spots in your gardens. It will supress weeds for the rest of the summer and you can dig it in, once Fall is here.
- Stake and tie up shrubs, vines and soon-to-be tall perennials, as required
- Early June is the time to plant tender summer bulbs, e.g. dahlias and glads for colour and cutting.
- And don’t forget the St. George’s Anglican Church Annual Giant Plant Sale, Saturday My 30 2026, corner of Russell & Bruce St. in Clarksburg. It opens at 8 AM. Come early for best selection. Hundreds of fine potted perennials, and shrubs to choose from at very competitive prices. Plus, get FREE GARDEN ADVICE from the experienced 599 Garden Club Experts in their green aprons.
John Hethrington,
Master Gardener Emeritus,
Past President, Master Gardeners of Ontario
Beaver Valley Probus Club