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

South, central, north and the Ozarks

MU Extension’s Vegetable Planting Calendar (G6201) uses a county map to divide Missouri into three planting regions: south, central and north. Each crop gets a planting window for each region. Where a fall crop is possible, the calendar lists a second set of dates below the spring dates.

The Ozark Plateau gets special treatment. G6201 tells Ozark gardeners to use the north dates, because the higher elevation brings later spring frosts and earlier fall frosts. Use the frost dates for your city above to confirm which set fits you.

Rain and snow also vary across the state. NOAA’s state climate summary puts average yearly precipitation at about 35 inches in the northwest and about 55 inches in the southeast. Northern Missouri averages more than 20 inches of snow a year, while the south gets less than 5.

What limits gardeners here

Drought and downpours. NOAA describes a state open to both floods and droughts. In the 2012 drought, May-through-July rainfall totaled only 5.8 inches, one of the driest growing periods on record. Meanwhile, heavy rain events have become more frequent. NOAA expects future summer droughts to grow more intense as higher temperatures dry soils faster. Plan for both: soil that drains after a downpour and a way to water through a dry July.

Storms and hail. With no mountains to block the air, cold, dry air from the north meets warm, moist Gulf air over the state. That produces severe thunderstorms with high winds, heavy rain and hail. A 2001 hailstorm along the I-70 corridor dropped stones up to 3 inches across.

Warm, muggy nights. NOAA reports that recent Missouri summers have had much warmer nights and that summer humidity has been trending up since the mid-20th century.

What MU Extension recommends

G6201 lists recommended varieties for each crop. MU calls them the “cream of the crop,” chosen for yield, quality and disease resistance under Missouri conditions. A few examples:

• Bush snap beans: Contender, Provider and Derby
• Pole beans: Kentucky Wonder and Blue Lake
• Beet: Detroit Dark Red
• Okra: Clemson Spineless
• Spinach: Bloomsdale Long Standing
• Tomatoes: Celebrity, Big Beef, Better Boy, Early Girl and Jet Star, with disease-resistance codes listed for each

For asparagus, G6201 recommends buying one-year-old crowns and not harvesting them the year you plant. The publication also includes a planning table with row feet to plant per person, seed needed and days to harvest, which helps you size the garden.

The fall garden

MU Extension horticulture specialist David Trinklein notes that warm days and cool nights in late summer suit a second round of cool-season vegetables. These fall crops are often more flavorful than the spring planting of the same crop. MU’s Missouri Environment and Garden newsletter adds this timing:

• Broccoli, cabbage, cauliflower and Chinese cabbage: set out four- to six-week-old transplants in early to mid-August. Plant in late afternoon or early evening to reduce transplant shock. Hot soil makes direct-seeded stands uneven.
• Collards, kale, mustard and turnips: sow through August. They’re ready in about 50 days.
• Lettuce and spinach: seed around the first week of September. Spinach often overwinters and yields well in April.
• Snap beans: sow in early to mid-August in most areas.

The main challenge is establishing crops in hot weather. MU advises watering right after you seed or transplant, and planting seeds a little deeper than in spring so they reach moist soil.

Before replanting, clear out spent plants, debris and weeds, since insects and diseases are drawn to fall gardens more than spring ones. Floating row cover helps keep pests off. Choose varieties by days to maturity and their ability to handle a light frost of about 26°F. If frost threatens tomatoes that have started to color, pick them and let them ripen indoors at about 70°F.

Soil testing

Before adding fertilizer or lime, test the soil. The University of Missouri Soil and Plant Testing Laboratory runs fee-based tests for homeowners as well as farmers. It provides fertilizer and lime recommendations meant to be economical and environmentally safe, and MU Extension explains how to collect and submit samples.