Timely Tips

What to Do in May 2026
Weekly Gardening Timely Tips from
Cornell Cooperative Extension of Westchester County

May 17 - 23

Perennials: Finish dividing overgrown fall-blooming perennials over the next few weeks. Use the divisions to fill bare spots in the garden if needed or share with friends. If invasive jumping worms are present, wash soil off plant roots and replace the plants in clean soil mix before they leave the site. Also consider native plants to fill gaps in blooming time to help provide continuity for pollinators. Provide an inch of water weekly, inclusive of rainfall, for establishment. Lightly mulch to conserve water, moderate soil temperatures and suppress weeds.

Flowers: When buying plants for flower beds, choose compact, bushy seedlings that haven’t yet flowered. It’s too early to plant many warm season annuals. Keep an eye on the weather and bring tender plants indoors at night. Thoroughly wash planters that were frequently used or filled with diseased plants. Refill with fresh potting mix.

Fruits and Vegetables: Continue to sow a succession of early crops, such as fast-maturing lettuce, radishes, carrots, beets and dill. Thin plants that need more space, mulch and water as needed. Remove flower stalks from rhubarb. If you haven’t already done so, prune out dead bramble canes and thin new canes to a recommended spacing: leave 3 to 5 healthy, vigorous canes per liner foot. Wait until the end of the month to plant warm season crops.

Trees and Shrubs: Finish planting balled and burlapped trees and shrubs as soon as possible.Nursery grown woody container plants have a wider planting window than balled and burlapped plants if given sufficient care, but these also do best planted when temperatures are moderate. Be on the lookout for the invasive spotted lanternfly. See Spotted Lanternfly | CALS for more.

Lawns: Are you confused about “No Mow May”? Skipping a whole month of mowing could be a disaster for a lawn. Lawn grasses that are not mowed often go to seed, producing thin, tough, and stemmy growth, and may create spaces for weed encroachment. Cutting the lawn to remove no more than ⅓ of the height of the blades at any given time helps to regulate the growth of the grass. This can help to prevent production of grass seed, and encourage better recovery from the stress of mowing, which in turn can support deeper roots and thicker growth. For example, when the grass reaches 4 inches in height, it is cut to 3 inches. Done every 2 weeks or so, this can save time, energy, and money. So, forget “No Mow May” and remember “Mow High in May, June and July” (a good practice for the whole growing season).

Houseplants:During especially mild spring days, it might be tempting to stick houseplants outdoors in the sun all day. Don’t. They need gradual exposure to outdoor conditions to move outside. Temperatures are usually sufficiently warm for many houseplants around Memorial Day or early June, but it may be a good idea to protect very tender tropical plants a few more weeks or until night air temperatures are consistently in the high 60s or low 70s°F. Consider the growing information in their native conditions to assess weather preparedness. For gradual exposure, bring plants into a shadier area for several hours at a time. Gradually expose them to more time outdoors until they are used to outdoor conditions, and it’s warm enough that they can spend the night outside.

Last updated May 17, 2026