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

The lake, the mountains and the Kingdom

Vermont is small, but its growing conditions vary a lot. A UVM Extension Master Gardener article on garden planning describes three broad patterns.

• The Champlain Valley: Lake Champlain buffers temperatures, so gardens near the lake in northwestern Vermont run warmer than northern sites farther from the water or higher up.
• The Northeast Kingdom: this is the coldest part of the state, with especially cold pockets in Orleans and Essex counties.
• Southern Vermont: the south is generally milder, but many mountain towns there are noticeably colder than the valleys around them.

These differences decide what grows well. Long-season crops like winter squash are easier in the warmer valleys and the south. Leafy greens do well in the colder areas and can be sown well into summer there. In hill country, treat the frost dates for your city above as a starting point and adjust for a garden that sits higher or farther from the lake than the town.

What limits Vermont gardens

A short season. The main limit is time. The UVM garden planning article notes that colder parts of the state also have shorter seasons, partly because the ground takes longer to warm in spring. Long-season crops are the first to struggle there.

Cold soil in spring. UVM’s Planting the Garden stresses patience. Warm-loving crops need warm soil as well as warm air, and plants set out too early just sit.

Acid soil. UVM Extension notes that most Vermont soils are naturally acidic or become more acidic over time, so many gardens need lime to raise pH. The two UVM articles cited here give slightly different targets. Garden Health and Soil pH puts the ideal for most vegetables and berries at 6.5 to 6.8, while Soil Test Now for Healthier Gardens in the Spring calls 6 to 7 optimal for most crops. Either way, the soil test sets the rate.

Pests and disease. Planting the Garden recommends:

• Buy transplants from local nurseries and greenhouses to avoid bringing in disease.
• Check plants for whiteflies and aphids before you buy.
• Put collars around new transplants to stop cutworms.
• Cover cucumbers, melons, squash and pumpkins with floating row cover to keep off cucumber beetles and the wilt they spread. Remove the cover once the plants flower so bees can pollinate.

UVM Extension’s planting order

Planting the Garden groups vegetables by how much cold they tolerate, timed from your frost-free date:

1. Very hardy: four to six weeks before the frost-free date. Potatoes, onion sets, peas, spinach, lettuce, collards and turnips, plus broccoli, cabbage and asparagus as transplants.
2. Frost-tolerant: two to three weeks before. Carrots, beets, radishes, parsnips and mustard from seed, plus cauliflower transplants.
3. Tender: on or after the frost-free date. Beans, sweet corn and summer squash from seed, plus tomato transplants.
4. Warm-loving: one to two weeks after the frost-free date, once the soil has warmed. Cucumbers, melons, pumpkins, peppers, eggplant and sweet potatoes.

For a fall crop, the same guide suggests sowing radish, lettuce, spinach, beets and turnips in late August so they mature in cool weather. For new gardeners, it recommends hybrids, All-America Selections winners and disease-resistant varieties, such as tomatoes marked VF for resistance to Verticillium and Fusarium wilt. It also suggests leaving cauliflower and head lettuce until you have some experience.

Stretching the season

A short season makes season extension worth the effort. UVM Extension Master Gardener Deborah Benoit’s Cheating the Season covers the main tools:

• Frost covers: sheets, blankets or an upside-down box thrown over plants on frosty nights, removed in the morning.
• Floating row cover: spun fabric over low crops, with heavier weights giving more cold protection. You can add plastic over the fabric as nights get colder.
• Low tunnels: fabric on hoops for taller plants, with the ends opened on warm days so plants don’t overheat.
• Cold frames: placed in a sunny, south-facing spot to keep kale, chard, spinach, carrots and beets producing into fall.

The same tools give spring crops an earlier start.

Lime by the numbers, not by guesswork

UVM recommends testing in fall so amendments can go on before spring. Use the UVM soil test form at go.uvm.edu/soiltest. The lab needs only a half to one cup of soil. The basic test reports pH, major and minor nutrients, organic matter, lime and fertilizer recommendations for the crop you name. Home reports refer you to the UVM Extension Master Gardener Helpline for questions.

When the report calls for lime, UVM Extension suggests:

• Use dolomitic lime if magnesium is low and high-calcium lime if magnesium is adequate.
• Split large applications between fall and spring.
• Wood ash can stand in for lime at two to three times the weight.

UVM also advises waiting until spring for most fertilizers and manure-based composts, which can be high in phosphorus. In fall, sow a cover crop such as winter rye, or mulch bare soil to protect it over winter.