Timely Tips

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

May 3-9

Perennials: Continue to plant perennials and install stakes for those that will become tall. Once asters, mums and other late blooming perennials have reached 6 inches or more, you may pinch them back to 4 inches. This helps to increase bushiness and fullness of bloom (and can delay flowering a bit). Stay out of the gardenwhen the ground is wet or when it’s raining to avoid compacting the soil and spreading plant diseases. Young spotted lanternfly (SLF) nymphs may be hatching soon. They are small, black with white spots, and move or jump readily when disturbed. Young SLF nymphs feed on perennials and other herbaceous plants before they are large enough to pierce the bark of woody plants.

Flowers:After spring bulbs finish blooming, you can remove (deadhead) the flowers, but don’t cut down foliage until it begins to fade to yellow. The leaves and green flower stalks help the bulbs make food to store for next year’s blossoms.

Fruits and Vegetables: With soil temperatures in the low 50s°F at a depth of 2 inches, you can still plant carrots, chard, and successions of fast maturing early greens if these can be watered adequately as the weather warms. Choose heat tolerant varieties wherever possible. After a warm spell, it may seem ok to plant tender crops, but the weather can be unsettled at this time of year. Even though the air temperature recently reached into the 80s°F in places, soil temperatures are still well below 70°F at a depth of 2 inches that is required for warm season plants to thrive. If peaches and plums have finished blooming, they may be pruned during dry weather. If black knot disease is present, remove the knots, making cuts about 8 inches below the infected growth. Check to see if brambles and grapes are properly attached to a trellis or arbor. Use soft ties to attach canes to the supports as needed.

Trees and Shrubs: Continue pruning spring-flowering shrubs (andromeda, azalea, forsythia, rhododendron, viburnum, etc.) after they’ve bloomed. Remove a few of the oldest stems to encourage new growth and shoots that are very small or thin. Take no more than ¼ to ⅓ of the total growth in each season.

Lawns: If indicated by a soil test, consider fertilizing around Memorial Day with a slow-release fertilizer. A low-maintenance lawn may not need fertilizer more than once per year, if at all, since nutrient cycling may be adequate in well-established turf. Cornell experts advise that fertilizing around Labor Day is preferable to earlier applications for a home lawn. Higher maintenance lawns may be fertilized around Memorial Day and Labor Day if needed.

Houseplants:If plants have been in the same pots “forever” and the soil is depleted, refresh it with new composted potting mix. Remove an inch or two of the old “soil” around the edge of a pot and fill the space with new mix or repot a plant into a container no more than 2 inches larger than the current pot. Use potting mixes that are formulated for specific types of houseplants.

Last updated May 2, 2025