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

Western, Central and Eastern Kentucky

The University of Kentucky’s Home Vegetable Gardening in Kentucky (ID-128) splits the state into three planting regions: Western, Central and Eastern Kentucky. Its gardener’s calendar gives each task a date for all three, and Eastern Kentucky usually runs about a week behind Central, which runs about a week behind Western. Onions started indoors, cole crops and the first spinach, pea and beet sowings all follow that pattern. The same one-week steps carry through to the fall sowings.

Use the region that matches your county as a starting point, then check the frost dates for your city above before setting out tender crops.

Rain: plenty on average, uneven in practice

The Kentucky Climate Center reports that the state averages 42 to 52 inches of precipitation a year, mostly as rain, with totals rising from southwest to northeast. Averages can mislead, though. Floods are most common in winter and spring, and droughts are most common in summer and fall.

For gardeners this means a wet spring that delays soil work, followed by dry stretches just as tomatoes, peppers and melons need the most water. ID-128 says vegetables need about 1 inch of water a week, from rain or irrigation, from April through September. Keep a rain gauge near the garden and water only to make up the difference. UK favors soaker hoses or trickle irrigation over sprinklers. The water goes straight to the roots and the leaves stay dry, so you can water in the evening without encouraging foliage diseases. Trickle systems use 30% to 70% of the water that overhead sprinklers need.

Disease pressure in warm, wet summers

Wet foliage is the main source of trouble in Kentucky tomato patches. The UK plant pathology fact sheet on foliar diseases of tomato (PPFS-VG-25) names early blight and Septoria leaf spot as the most common fungal diseases of tomato in Kentucky. It adds that target spot, once thought to be limited to subtropical areas, has recently become common in Kentucky plantings. Disease usually starts in early summer and continues through the season.

The fact sheet’s cultural advice:

• Don’t plant tomatoes in the same spot for 2 to 3 years. For early blight, also keep potatoes and eggplant out of that rotation, since they are hosts too.
• Choose resistant or tolerant cultivars. Cherry, grape and hybrid types usually hold up better than slicers and heirlooms.
• Pick a site in full sun with good air movement, space plants for their mature size, and keep weeds down so foliage dries quickly.

ID-128 also warns against planting tomatoes, peppers or eggplant near black walnut trees. Plants near walnuts or decaying walnut roots can wilt and die suddenly after they set fruit.

Soil: test, then lime or amend

ID-128 recommends a soil test, preferably in October or November, before you add any lime or fertilizer. The standard test measures pH, available phosphorus and potassium, and other nutrients on request. Most vegetables grow best between pH 6.2 and 6.8. The guide includes tables of agricultural limestone rates for raising pH and powdered sulfur rates for lowering it.

Avoid heavy clay if you can choose your site, and work in organic matter to loosen clay or to help sandy soil hold water. If water stands because of rock or a hardpan layer underneath, raised beds may be the practical answer. Grey colors in the subsoil indicate poor drainage.

Three gardens a year

ID-128 plans the year as three gardens.

• Spring: cool-season crops planted as soon as the soil can be worked. They grow best at 50°F to 65°F, and if planted late, summer heat makes them bolt or turn bitter.
• Summer: warm-season crops planted once frost danger has passed, along with cool-season crops that can finish in the heat.
• Fall: sown from July into August. It includes final plantings of sweet corn and bush beans plus frost-tolerant crops such as beets, Bibb lettuce and broccoli. Cool nights slow growth, so fall crops take longer to mature than the seed packet suggests.

Getting a soil test

Kentucky gardeners get soil tested through their county Extension office. Let the sample air-dry for about two days, then take it in. The University of Kentucky’s Division of Regulatory Services runs the soil testing laboratory in Lexington, and its reports include fertilizer and lime recommendations.