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

From the Missouri River to the Panhandle

Nebraska looks flat, but the Nebraska State Climate Office at UNL notes that the land rises about 4,000 feet from east to west toward the Rockies. Gulf of Mexico moisture reaches the low eastern side far more easily. Average yearly precipitation ranges from about 36 inches in the far southeast to under 15 inches in the western Panhandle. Rain peaks in May and June and is lowest in January.

Temperature follows a similar gradient. The annual average runs from the mid-40s °F in the northwest to the low 50s in the southeast. Western Nebraska winters tend to be sunnier and somewhat milder because of downslope winds off the Rockies. Even so, the west and north drop to -20°F or colder more often than the rest of the state. Sitting mid-continent, Nebraska is exposed to both arctic air from the north and hot air from the southwest, so spring and fall weather can swing hard. Check the frost dates for your city above. The climate office also reports a trend toward fewer but more intense droughts.

What limits Nebraska gardens

Cold soil in spring. Nebraska Extension’s NebGuide Soil Temperature: A Guide for Planting Agronomic and Horticulture Crops in Nebraska (G2122) argues for planting by soil temperature rather than the calendar. Its table gives approximate minimum soil temperatures at planting:

• Spinach: 38°F
• Radish: 40°F
• Lettuce and onion: 41°F
• Pea: 42°F
• Potato and cabbage: 45°F
• Carrot: 46°F
• Sweet corn: 55°F
• Pepper, snap beans and tomato: 57°F
• Cucumber: 58°F
• Pumpkin: 60°F

On average, soil reaches 55°F about a week later in central Nebraska than in the southeast. Most of the Panhandle lags about two weeks behind the southeast. The guide also found that soils warmed earlier in the 2000s than in the 1990s, but year-to-year swings are still large.

Hail. Nebraska Extension’s hail fact sheet says hail is more frequent in the Great Plains than elsewhere in the country. About 70 percent of the state’s hail reports fall between May and July. From 2003 to 2012 the state averaged 7 to 11 severe hail days a year. Hoops covered with floating row cover help protect vegetable beds.

Alkaline clay. The Lancaster County Extension office notes that many eastern Nebraska soils that have never been farmed are naturally pH 7.5 or higher. Nebraska’s clay soils are also strongly buffered, so they drift back to their original pH after sulfur is added. Extension suggests choosing plants that tolerate higher pH rather than fighting the soil. It also warns against three common amendments:

• Wood ash is very alkaline.
• Sand mixed into heavy clay sets up like concrete.
• Gypsum neither lowers pH nor “sweetens” soil and only helps on salty ground.

Fall is a second season

Nebraska Extension’s NebGuide Fall Vegetable Gardening (G1343) calls July and August planting an excellent and often overlooked practice. Cool-season crops maturing in short, cool autumn days often taste sweeter and milder than spring crops. Cole crops benefit most. Lettuce and spinach are less likely to bolt. The guide adds that in Nebraska the first frost is often followed by a few more weeks of good growing weather. Hardy crops such as cabbage, broccoli, Brussels sprouts, carrots, turnips and kale keep growing until temperatures drop to about 20°F.

To time fall plantings, count back from your first expected fall frost. Add together the crop’s days to harvest, its transplant-growing time if you start your own, and the expected harvest period. Then add about 14 days as a “fall factor” for slower growth. Frost-tender crops such as beans, cucumbers, squash and tomatoes get another 14 days.

The guide also gives tips for midsummer sowing:

• Plant seeds about twice as deep as in spring.
• Water lightly two to three times a day in very hot weather.
• Shade the soil with a board or light mulch for lettuce, peas and spinach, which germinate poorly when the soil is above 85°F.
• Watch for cucumber beetles and squash bugs, which peak in August.

Varieties and soil testing

Nebraska Extension’s Selected Vegetable Cultivars for Nebraska (G1896) lists cultivars that should succeed in most areas of the state. For tomatoes these include Better Boy, Big Beef, Bush Celebrity and Mountain Pride for slicing, Sungold and Sweet Million for cherries, and Amish Paste and San Marzano for sauce.

Before amending, test. The Lancaster County office lists commercial labs such as AgSource in Lincoln and Midwest Laboratories in Omaha. Take 10 to 15 cores 5 to 6 inches deep, mix them, and send 1 to 2 cups. Ask for residual nitrogen, phosphorus, potassium, organic matter, CEC and pH. Add any sulfur or lime in fall so it has time to react.