Gardening in Oklahoma

Hardiness zones in Oklahoma

Oklahoma spans USDA hardiness zones 6b through 8a. A hardiness zone tells you the average annual minimum winter temperature for a location, not the whole climate. Each zone covers a 5 °F (2.8 °C) band, and a higher number means a milder winter low. Zone 6b marks the coldest parts of the state, while zone 8a marks the warmest. The full range recorded across Oklahoma includes 6b, 7a, 7b, and 8a. This number says nothing about summer heat, rainfall, humidity, or soil type. Two towns in the same zone can still see very different summers. Use the zone to judge which perennials and woody plants can survive your coldest nights. Pair it with your local frost dates before you plan when to plant. A seed packet or nursery tag that lists a zone range is telling you about winter survival, not planting timing. Check your specific zone against the state's range to see where your garden sits.

• Zone 6b
• Zone 7a
• Zone 7b
• Zone 8a

Frost dates

Your frost dates mark the start and end of your safe growing season. Across Oklahoma's weather stations, the last spring frost at 50% probability can fall as early as March 15. In cooler parts of the state, it can fall as late as April 26. The first fall frost at that same probability arrives as early as October 17 in the coldest spots. In the mildest spots, it arrives as late as November 15. That spread of about a month in both spring and fall shows how much local conditions shift the calendar. Instead of planting by a fixed date, count forward from your own last frost date and back from your own first frost date. Tender vegetables and warm-season flowers go in the ground after your local last frost date, not one borrowed from another part of the state. Cold-hardy crops can often go in a few weeks earlier, timed to your own last frost rather than a month on a calendar. These dates come from 182 weather stations across Oklahoma, so records near you will narrow the range further.

Climate

Oklahoma's climate data for this guide comes from 182 weather stations spread across the state. Winter hardiness zones recorded here range from 6b in the coldest areas to 8a in the warmest. That gap shows a real split in how cold winters get across the state. That same split shows up in frost timing. The last spring frost at 50% probability ranges from March 15 to April 26. The first fall frost at that same probability ranges from October 17 to November 15. Together those dates set a growing season that runs from 173 days at its shortest to 244 days at its longest. A gardener in a short-season area plans around roughly six months of safe growing. A gardener in a long-season area can count on closer to eight months. None of these figures describe summer heat, humidity, or average rainfall, since the data here covers only hardiness zone, frost timing, and season length. Check your nearest station's figures rather than a statewide average. Oklahoma's range between zones 6b and 8a is wide enough that a single number for the whole state would mislead you. The safest approach is to match your planting plan to the zone and frost dates for your own location.

Season length

How long your growing season lasts depends on where in Oklahoma you garden. The shortest recorded season runs 173 days from last frost to first frost. The longest recorded season runs 244 days. That is a difference of more than two months between the state's coolest and warmest areas. A short season favors fast-maturing vegetables and flowers you can start and finish within about six months. A long season gives you room for crops that need a longer stretch of warm weather, or for a second planting after an early harvest. Match your choice of plants and planting dates to the season length for your own part of the state, not to either extreme.