The answer is… it depends. You have two important guides when you’re assessing if it’s okay to plant: is your ground thawed and workable, and when is your average last frost date?
Is the Ground Workable?
Many trees and shrubs can be planted as long as your soil is fully thawed and not too soggy from the melted snow and ice. You should be able to get a shovel into the ground easily, and not see or feel any ice as you work the soil through your hands. The soil should hold its shape and texture as it normally would. Trees and shrubs are still dormant until new growth appears, and can be planted or transplanted while still dormant. Trees and shrubs often have roots that travel deep into the ground, below the frost line, so a light morning dew with some frost will not hurt or disturb them significantly.
Last Frost Date
Another indicator is your average last frost date. Scientists track this data every year and report the accumulated average, so it’s an “official” estimate, but not a guarantee – Mother Nature loves surprises. On the Seacoast, here in New Hampshire, our average last frost date is May 15. This is the average date when we experience the last light freeze of the winter. Degrees of freeze are measured like this:
- Light freeze: 29° to 32°F (1.7° to 0°C)—tender plants, like many Annuals, are killed.
- Moderate freeze: 25° to 28°F (3.9° to -2.2°C)—widely destructive to most vegetation (unless the plant is dormant).
- Severe freeze: 24°F (-4.4°C) and colder—heavy damage to most garden plants (unless the plant is dormant).
Starting Plants from Seed
Many gardeners love to grow vegetables and flowers from seed. If you are starting plants from seed, read the back of each packet, which will instruct you on when to sow indoors or outdoors, often using the last frost date as your guide. Try to align a growing calendar with plants that like being sown at roughly the same time. Botanical Interests and the Old Farmer’s Almanac have excellent growing guides to help you plan this.
Annuals and Perennials
In spring, gardeners are jonesing for flowers and color, and impatient to get started. Because the roots and foliage of many annuals and perennials can be tender and often grow closer to the frost line, they can be more affected by shifting temperatures. We recommend using containers to plant cool-tolerant annuals like Pansies, Violas, Senetti, Ranunculus, and spring bulbs before the last frost date. You could also use cool-tolerant perennials like Basket-of-Gold, Forget-Me-Nots, Lavender and Herbs in containers. Most days, these plants can be left outside happily, and if temps dip below freezing, you can just bring the containers indoors (a garage or shed are perfect) until the cold snap passes. Or, you can throw a cloth over them during cold snaps: Bed sheets, drop cloths, or light blankets make suitable covers for vulnerable plants. Woven fabrics are better than solid ones such as plastic. As temps stay reliably above freezing, you can then plant your annuals and perennials into the ground.
So in closing, evaluate your soil, study up on the plants you want to grow, understand what they can or cannot handle, and be ready to protect certain plants from cold snaps the dip below freezing. This way, you can get an early start on gardening, and keep your plants happy and healthy. Enjoy!