Gardening in Rhode Island: zones, frost dates and when to plant

Coast, bay and western uplands

Rhode Island’s weather comes from two directions. NOAA’s state climate summary describes the state as exposed both to cold winter and warm summer air from the continental interior and to mild, moist air off the Atlantic. That mix is why the weather changes so often. Providence averages around 74°F in July and about 29°F in January, and the state gets roughly 46 inches of precipitation a year.

Snowfall shows how much the ocean matters within such a small state. Block Island and the southeastern shores of Narragansett Bay average about 20 inches of snow a year, while the western part of the state gets 40 to 55 inches. Even a single town can have pockets that run cooler or warmer than the frost dates for your city above suggest, and URI’s planting calendar tells gardeners to allow for these microclimates.

What limits Rhode Island gardeners

• Acidic soil. URI says native, uncultivated soils across southern New England typically test between pH 4.5 and 5.5. That’s ideal for blueberries, rhododendrons and azaleas, but most vegetables want 6 to 7. In soil that acidic, nutrients are tied up and plants struggle.
• Storms. Nor’easters, coastal storms, severe thunderstorms and the occasional hurricane are part of the climate. Hurricane Irene in 2011 brought southeast winds up to 70 mph, and heavy downpours have become more frequent since the mid-1900s. NOAA rates the coastline as highly vulnerable to flooding from winter storms and hurricanes.
• Late cold. When to plant vegetables is the second most common spring question at URI’s hotline. Its answer is to hold tender crops like tomatoes and peppers until after the last frost, while hardy crops such as snap peas and spinach can be seeded earlier.

Using URI’s planting calendar

URI Cooperative Extension’s Rhode Island Planting Calendar for Fruits and Vegetables (R03) is the state’s main planting guide. It runs from February through October in half-month steps and marks each crop with a code: start seeds indoors, direct seed in the garden, transplant indoor-grown seedlings, or plant cloves or crowns. It also gives the days to harvest. Some patterns stand out:

• Tomatoes, peppers, eggplant, leeks and celery are started indoors well before they go out. Tomatoes take 50 to 75 days from transplant to harvest.
• Lettuce for cutting, radishes, beets, carrots and kohlrabi have many seeding windows, so you can sow small amounts again and again instead of all at once.
• Broccoli, cauliflower and head lettuce get a second round of indoor starts for later transplanting.
• Garlic is planted as cloves and needs 5 to 7 months. Asparagus goes in as crowns and takes one to two years before harvest.

The calendar’s dates assume one statewide frost window. Shift them earlier or later to match your city’s frost dates and your own garden. URI also reminds gardeners to harden off transplants. The hotline suggests setting new plants outdoors for five to seven days in a spot sheltered from wind and direct sun, and bringing them in at night, before planting.

Soil testing and help from URI

URI Master Gardeners run free soil pH testing from March through October. Their Gardening Information and Soil Testing (GIST) program takes samples at the Kingston campus on weekdays, by mail, and at community events around the state. To collect a sample, dig about half a cup of soil from 4 to 6 inches deep, air-dry it on newspaper (wet soil can’t be tested), and bag it. Along with the result, volunteers recommend how much lime to add, if any. Lime takes two to three months to change pH, and spring applications don’t take effect until early summer, which is why URI favors fall liming. For a full nutrient or lead analysis, URI refers gardeners to the soil labs at UConn and UMass. It suggests retesting every few years, and especially when building new beds.

URI also recommends working compost into every garden. For problems, the free Gardening and Environmental Hotline, staffed by Master Gardeners, takes calls at (401) 874-4836 and email with photos at [email protected]. Volunteers advise scouting the undersides of leaves and identifying a pest before spraying anything.