May is when the real garden planting season begins, but that doesn’t mean everything gets planted at the same time. Some crops or plants benefit from early starts and others are endangered or damaged by the last frosty nights in mid-spring. The timing suggestions here won’t apply equally to everyone, since conditions vary even within Western New York, but some basic principles should help.
Decision makers: The last frost date and soil temperature
Tender plants can die quickly when a sudden freeze crushes their cells. Equally important is the weather pattern before and after that last frost, since the warm and cold periods affect the soil temperature. That temperature changes much more slowly than air does and is a key factor in the health and happiness of seeds and young plants. In a time of extreme and rapid weather changes, making decisions about the last freeze or frost date is trickier than ever. Start with estimating the last likely frost date.
The last average frost date in WNY occurs sometime in late May, depending upon location. It is the night when a light freeze (twenty-eight to thirty-two-degrees Fahrenheit) kills tender vegetation. Notice the word “average.” If the National Oceanic and Atmospheric Administration (NOAA) says that the average last freezing temperature is May first in inner Buffalo but May 18 in some Southtowns, we must remember what average means. There is a thirty percent probability that the last killing frost will occur two weeks sooner or two weeks later. After decades of personal experience, and advising gardeners through Cornell Cooperative Extension and at Lockwood’s Garden Center, I have concluded this: if May 21 is your last average frost date, a wise gardener does not expose annuals (impatiens, petunias) or plant tomatoes in soil until about May 30.
We have many frosty nights on Memorial Day weekend. If you are determined to plant tender annuals or warm season vegetables outside sooner, prepare to cover them on the coldest nights. (Warm season vegetables like tomatoes, eggplants, beans, squash, melons, and cucumbers can show growth defects from planting in cold, wet soil.) Several university studies have shown that a tomato planted June first in warm soil may quickly catch up with the tomato planted in early May, at risk of frost damage or other defects. In protected pockets in the city, this advice may be too conservative; here, there are microclimates where gardeners can plant sooner without negative results.
When to plant flowers, shrubs,
Trees, shrubs, and perennials also have ideal planting times, but early in the season is ideal. Remember, most hardy plants have been stored outdoors in professional garden centers or nurseries for many weeks (or all winter). Or they have been hardened-off if they were shipped from warmer places or grown in greenhouses. Warning: beware plants that were shipped into box stores or indoor locations without being gradually acclimated to cold nights. Just check what the plant has experienced before it goes outside at your house. You can plant many annual flowers from seed; look for them and read the timing on the seed packets. Some go outside in May and others want warm soil.
Home gardeners and landscapers have been planting woody plants (trees and shrubs) as soon as the soil was penetrable—and you can proceed to plant these throughout the season, as long as you can ensure deep and proper watering all season as the roots become established. Bareroot plants (most of them locally produced at Turnbull’s Nursery) should be planted before bud break, when leaves start to open. Perennial plants can be planted when the soil is workable and does not cake or compact when you put those roots in the ground. Try to plant as many locally native plants as possible; our ecosystems and pollinators need them and they are most likely to tolerate real conditions here.
Tender or semi-hardy annuals
Garden center folks can tell you which annual plants (or tender perennials often sold as annuals) handle a couple of frosts or cold nights well. Pansies, for instance, love some chilly nights. But if the plants are called tender, then enjoy them in baskets or planters in May, but prepare to cover or move them on nights that threaten temps in the forties. (Specific tolerance varies.) Many tropical plants, such as Mandevillas, don’t grow well until temperatures consistently remain above fifty-five degrees Fahrenheit, which explains why the growers at professional garden centers may be reluctant to sell them while the nights are still cold. Read tags; ask questions.
There is so much more to learn, beyond when to plant. I recommend classes, online learning, and especially garden books relevant to where you live. Eventually you will know how to prepare your soil, plant and water, handle spacing and layout, and what steps to take to block and deter pests and prevent diseases. Then plant at the right time. And if you make mistakes, remember that we all have done that. It’s a process!