Gardening in Massachusetts: zones, frost dates and when to plant

East and south first, west and north later

Massachusetts is a small state, but planting time still moves across it. UMass Extension’s Vegetable Planting Chart notes that planting can start earlier in eastern and southern Massachusetts and runs later in the western and northern parts of the state. In the west and north, lean toward the late end of any planting window; in the east and south, you can usually start sooner. Check the frost dates for your city above and plan from there.

The coast brings its own risk. NOAA’s state climate summary describes the coastline as highly exposed to nor’easters, tropical storms and hurricanes. Inland areas are not spared heavy rain either: in late August 2011, Hurricane Irene dropped more than 4 inches on a number of stations in central and western Massachusetts.

What limits gardeners here

The main limit is season length. UMass Extension’s Planning a Vegetable Garden fact sheet says many warm-weather crops are grown from transplants because the Massachusetts season is too short to sow them in the garden. Tomatoes, peppers and eggplant almost always go in as started plants.

The climate is also shifting. NOAA reports that Massachusetts temperatures have risen almost 3.5°F since the start of the 20th century. Hot days have been well above the long-term average since 2010, and warm nights have been climbing since 1995. NOAA expects more extreme rainfall and warns that warmer temperatures and earlier snowmelt may make droughts worse. In practice that means planning for both downpours and dry spells: mulch, water evenly and keep the soil well drained.

How UMass Extension times the garden

The Vegetable Planting Chart puts crops in three groups:

• Cool weather crops such as arugula, beets, carrots, lettuce, peas, radishes, spinach, broccoli, cabbage, kale and potatoes. Many can go in during late winter or early spring, as soon as the soil is dry enough to work. Many can be planted again in succession for a fall harvest.
• Intermediate crops: basil, beans, corn, cucumbers, melons, pumpkins and summer and winter squash. These go in after the cool crops and before the warm ones.
• Warm weather crops: eggplant, peppers and tomatoes. Set out transplants only after all danger of frost has passed.

The Planting a Vegetable Garden fact sheet adds detail. Hardy transplants like broccoli, cabbage, lettuce and Brussels sprouts can go out about two weeks before the average last frost. Tender crops should wait until frost danger is over and both the air and soil have warmed to 60-65°F. Harden off home-grown seedlings first by giving them gradually longer periods outdoors and watering a little less, without letting them wilt.

Site matters as much as timing. UMass recommends 6 to 8 hours of sun for most vegetables. Tomatoes, peppers and squash need a full day of sun, while lettuce and other leafy greens can handle some shade.

Tomatoes in Massachusetts

UMass Extension’s tomato fact sheet recommends varieties developed for the Northeast over hard, bland shipping types. Heirlooms are worth trying, but most lack disease resistance. To lower the risk of Verticillium and Fusarium wilt, plant them where tomatoes, peppers, potatoes, eggplant, brambles or strawberries have not grown for a few years.

Late in the season, once nights drop below 60°F, tomatoes taste better if you pick them as they start to color and let them ripen at room temperature.

Lime, compost and soil testing

Start with a soil test. UMass Extension advises spreading ground limestone at the rate the test recommends. Work a 2-inch layer of compost into the top 6 inches of soil, and add more organic matter if your soil is sandy or heavy clay.

There is a lime issue particular to this state. According to UMass, most limestone sold in Massachusetts is dolomitic, which is high in magnesium. Years of dolomitic lime can leave a garden high in magnesium and low in calcium. Use calcitic lime about every other time, or add gypsum to supply calcium.

Compost can also overshoot. The Fertilizing the Vegetable Garden fact sheet warns that heavy, repeated compost use can build up nitrogen and phosphorus. It sets a goal of nutrients in the high (optimum) range and organic matter between 5 and 8 percent. UMass fact sheets differ on how often to test: every three to five years for the general garden, every two or three years for tomato beds.

The UMass Soil and Plant Nutrient Testing Laboratory in Amherst measures nutrients, pH and lime needs. It can also flag elevated lead and other toxic heavy metals.