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

A state of two climates

Kansas looks uniform on a highway map, but it splits sharply between east and west. The Kansas Office of the State Climatologist at Kansas State University reports average yearly precipitation of more than 45 inches in southeastern Kansas and less than 18 inches in the southwest. Most of that moisture comes up from the Gulf of Mexico and reaches the southeast corner first, so rainfall drops off as you head northwest.

Temperature runs east to west too. The annual mean is close to 58°F along the Oklahoma line and under 52°F in the northwestern corner. That means a garden near Goodland and one near Pittsburg follow different rules even when they share a planting calendar. Check the frost dates for your city above and adjust from there.

What limits Kansas gardens

Wind. K-State’s Kansas Garden Guide (S51) says wind protection is worth having at most Kansas sites. Use fences, shrubs or buildings as a windbreak. For summer winds the screen belongs on the south or southwest side of the garden. Hot, dry wind hits containers hardest. The guide suggests nothing smaller than a 12-inch pot, since bigger pots hold moisture longer and are less likely to blow over.

Heat and dry spells. The guide notes that summer watering costs both money and time, and that plants under long water stress give lower yields and poorer quality and resist pests less well. Raised beds dry out faster than in-ground rows, so they need more water during heat and drought.

Alkaline soil. Most Kansas soils lean alkaline, though some areas have turned acidic under certain cropping and fertilizer histories. In high-pH soil iron is often the missing micronutrient, and the plants turn pale yellow. A foliar iron spray or lowering the soil pH fixes it. K-State also warns against putting wood ashes in compost unless your soil is acidic, since ashes push pH higher.

Using K-State’s planting calendar

K-State Research and Extension’s Vegetable Garden Planting Guide (MF315) is the state’s standard planting chart. It shows a primary planting window for most of Kansas and a wider “marginal” window that may work in some years. The guide says every window may need to move earlier or later depending on the season’s weather, the variety, how you want the harvest to taste and where in Kansas you live. MF315 also lists expected yields per 10 feet of row and how much to plant per person. It points out that even a 100-square-foot plot can supply a good share of the vegetables for a family of four.

The Kansas Garden Guide sorts crops into two groups:

• Cool-season crops such as lettuce, spinach, radishes, carrots, broccoli, cabbage and beets. Many tolerate frost and grow in soil as cool as 45°F, but they often struggle in summer heat. Plant them before the last spring frost.
• Warm-season crops such as tomatoes, peppers, melons, squash, sweet potatoes, corn and beans. They can’t take frost and want soil at 55°F or warmer, so plant them after frost danger has passed.

The guide also points to the Kansas Mesonet as a source of weather data for timing planting in years that run unusually warm or cold.

Fall gardens

K-State calls fall an excellent and often overlooked season in Kansas. Vegetables that ripen in cool fall weather often taste better than those ripening in the hot, dry end of spring and summer, and many can stay in the garden into winter. A fall garden takes planning that starts in early summer.

Fall gardens bring their own problems. Pests build up over the summer, and seeds sown into very hot soil germinate poorly. K-State suggests starting lettuce, cabbage, broccoli, cauliflower, Chinese cabbage and collards in pots somewhere cooler, or under lights, for about four weeks. Harden them off for several days before moving them to the garden. The fall dates in the Kansas Garden Guide are written for central and eastern Kansas. Gardeners in northwestern Kansas should plant 10 days to 2 weeks earlier, and those in southeastern Kansas 10 days to 2 weeks later. Go easy on fertilizer at this time of year, because heavy doses can damage young plants.

Test the soil first

The Kansas Garden Guide recommends testing a new garden’s soil the winter before you plant, to learn its pH and nutrient levels. Without a test, fertilizer is guesswork. Collect about a pint of soil and take it to your local K-State Research and Extension office. The agent will either run the test in a county lab or send it to the Kansas State University soil testing laboratory, then recommend how much fertilizer to use.