Timely Tips

What to Do in May 2025
Weekly Gardening Timely Tips from
Cornell Cooperative Extension of Westchester County

May 24-31

Perennials: Spring flowering perennials are glorious at this time of year! Enjoy and keep up with regular scouting for insect and disease presence that may need addressing.

Flowers: If the soil has reached 70°F at a depth of 2 inches, tender summer bulbs like cannas, crocosmia, dahlias, and gladiolas can be planted. Plant warm-season annuals like browallia, coleus, cosmos, impatiens, marigold, petunia, and verbena when nighttime air temperatures are consistently above 55°F and soil temperature has reached 70°F at a depth of 2 inches. Very tender annuals like begonia, celosia, cleome, geranium, impatiens, nicotiana, portulaca, salvia and zinnia are best transplanted outdoors after Memorial Day. When filling a hanging basket, window boxes, or other container with plants, use potting mix, not soil from the yard or topsoil. Potting mix is free of weed seeds and is less dense than many ambient soils, allowing roots to grow well and water to drain, which in turn helps to prevent root rot.

Fruits and Vegetables: Warm season vegetables require soil above 70°F to do their best – eggplant and other tropical vegetables prefer soil temperatures above 80°F. In particularly warm areas, consider direct seeding cucumber, squash and melon, and harden off tomato, eggplant and pepper seedlings. Gradually expose seedlings to the outdoors before planting. Set seedlings outside for up to an hour the first day and protect them from direct sun and wind, gradually increasing their outdoor exposure every day. When the plants can remain in full sun all day and spend a warm night outdoors, they’ll be ready for transplanting. Be prepared to protect tender seedlings if temperatures dip. Remember to put plant supports like stakes in place before the planting or seeding. This will avoid harm to young plants as they grow.

Trees and Shrubs: Needled evergreens vary in their ability to tolerate various types of pruning. Identify the type of plant before removing any growth. When pruning most evergreens, do not prune back further than the limit of the green foliage. Local Cooperative Extension offices can help you identify plants and provide pruning information. Hire an arborist to work on large trees.

Lawns:When grass has grown to about 4-inches tall, cut it back to about 3 inches. Continue to mow on a 2-week schedule to regulate grass growth. When following the “⅓ rule”, clippings can more easily filter through grass blades and protect the grass crowns. Leave cuttings on the lawn for a natural mulch and to return nutrients to the turf. Remember to “Mow High in May, June and July.” If needed by soil testing, lawn fertilizer can be applied now. Fall is the best time to fertilize, especially for lower maintenance lawns, when the grass uses the nutrients to store and prepare for winter.

Houseplants: If houseplants are outdoors, make sure they’re protected from wind and direct sun. Fertilize houseplants as needed to replace nutrients lost due to increased watering and growth. Use a balanced fertilizer according to label directions.

Last updated May 23, 2025