by Marilyn Odneal, Horticulture Adviser
One of the best features about our streaming weather station at the Missouri State Fruit Experiment Station is that you can look at the soil temperature at both 2 and 4 inch depths anytime you want to, and you can look at the fluctuation every five minutes. I looked at it yesterday and it was in the upper 40s, but today, it is down to the lower 30s. This may not be considered spine-tingling excitement to everyone, but to me, it is better than reality TV.
If you are planning to sow seed directly into the garden rather than beginning the seed indoors, soil temperature is key information. The soil temperature at which your seed germinates best differs from species to species. Here are some lowest/minimum and best/optimum germination temperatures for several garden vegetables based on a list by J. F. Harrington of the University of California, Davis.
Bean – Minimum 60⁰F; Optimum 60 – 85⁰F
Cabbage – Minimum 40⁰F; Optimum 45 – 95⁰F
Corn – Minimum 50⁰F; Optimum 60 – 95⁰F
Okra – Minimum 60⁰F; Optimum 70 – 95⁰F
Onion – Minimum 35⁰F; Optimum 50 – 95⁰F
Pumpkin – Minimum 60⁰F; Optimum 70 – 90⁰F
Radish – Minimum 40⁰F; Optimum 45 – 90⁰F
Tomato – Minimum 50⁰F; Optimum 60 – 85⁰F
For a complete list online, go to the Alabama Cooperative Extension publication “Soil Temperature Conditions for Vegetable Seed Germination” at http://www.aces.edu/pubs/docs/A/ANR-1061/ANR-1061.pdf
The University of Missouri Extension has a vegetable planting calendar available online at http://extension.missouri.edu/p/G6201
Before direct seeding, cultivate the garden area 6-10 inches deep and rake the surface smooth, remove rocks and break up clods of soil. Plant seeds in rows and cover to the depth indicated on the seed packet. Firm the seed in the soil so there is good seed to soil contact (you can lightly walk over the row like a tightrope to tamp them in). Make sure to keep the seedbed moist but not overly wet until the seeds grow. After growth, thin the plants according to the instructions on the seed packet or garden guide.
The Mountain Grove online streaming weather station is located at http://agebb.missouri.edu/weather/realtime/mountainGrove.asp; however, if you don’t have a soil thermometer or access to local soil temperature data in your area, don’t worry. It is usually safe to sow the seed outdoors when trees are beginning to produce leaves.
Direct comments or questions concerning this column to Marilyn Odneal via email at MarilynOdneal@missouristate.edu; write to Missouri State Fruit Experiment Station, 9740 Red Spring Road, Mountain Grove, Mo. 65711; or call (417) 547-7500. Visit our Web site at http://mtngrv.missouristate.edu.