Panhandle Plantings
The Secret of Seed Germination
by Val Ford, Holmes County Master Gardener
It's February. Do I need to remind you to plant your potatoes on Valentines Day? If any of you are like me, you're beginning to get the planting itch (sometimes it feels more like the shingles!). The risk-takers in the group are starting their seedlings indoors in anticipation of an early start. The more conservative lot is counting the days to March 25 - the median day for our last frost in Northwest Florida.
For those of us who start at least part of their spring vegetable garden (or flower garden for that matter) from seed, patience is a powerful ally. For germination to occur and produce strong seedling growth, soil temperature is probably the most important factor to be considered. The majority of gardeners have a basic understanding of warm-season versus cool-season plantings, but don't really understand the "whys' and "wherefores." What's that "old saying?" You don't know a man until you've walked a mile in his shoes? That same 'old saying' goes for gardening - in order to understand what's happening in the garden, you must think like the metaphorical carrot (or carrot seed in this case). OK - a bean or radish or tomato will do - but put yourself in place of the plant and use your noggin to solve your problem! Here goes . . . .
Every type of seed has an optimum germination soil temperature, the temperature that maximizes root and shoot development in the shortest period of time. This is somewhere between the minimum and maximum soil temperatures given on most seed starting charts. Keep in mind that the closer we are to the minimum soil temperature, the longer the germination period will be, and the lower the successful germination rate. The same is true as we approach the maximum soil temperature. What we're really striving for is the 'realistic' soil temperature, which is a combination of soil temperature and the surrounding environment.
Let's 'become one' with our carrot seed. According to the Alabama and Auburn Universities web site, the minimum and maximum soil temperatures for carrot seed germination are 40 F and 100 F, respectively. This translates into an optimum soil temperature range of 45 -85 F, and an optimum temperature of 80 F for maximum seed germination. We all know that carrots are 'cool season' vegetables in our area - so what gives with such high soil temperatures?
The trick is to plant at a time when soil temperatures will realistically provide for the highest percentage germination rate, and the surrounding environment will provide for seedling strength and vigor. Thus, we can seed our winter garden (i.e. the carrot seed) in late summer while the soil temperatures are warm, the days are shortening, the sun is getting lower in the sky, the evenings are cooling off and hopefully, the humidity is lowering. Why do we want to consider these factors? Because once we've maximized seed germination, we must consider seedling survival and strength in order to accomplish the harvest of our dreams.
The reverse is true for our summer gardens, which is why so many of us resort to tomato transplants instead of direct seeding. The optimum range soil temperature for a tomato seed to germinate is 70 -95 F - tough for us to accomplish in mid-to-late March. BUT - we can start those tomato plants indoors and transplant to a garden that is warming up (as long as we avoid frost) because a tomato can tolerate air and soil temperatures as low as 50 F, although growth will be slow until soil temperatures warm up.
How does one maximize appropriate soil temperatures? In the summer we mulch to retain soil moisture - but there's another reason. Moist soil retains heat better - so we mulch to protect the root zone from direct sun and keep the soil from overheating. In the winter we remove mulch and work hard to retain soil moisture (wind depletes moisture faster than sun) - because a moist, bare-ground root zone retains solar heat better than mulched, dry soil.
For those who don't 'guess' well, a probe thermometer can be used to take soil temperatures. It's best to use them at mid-day in an area out of direct sun. For cool season vegetables, the soil temperature should be taken at a 2-inch depth. For warm season vegetables, a 4-inch depth is appropriate.
Now that we've covered the most important factor for successful seed germination, let's address the most common cause of poor seed germination - planting depth. The smaller the seed, the less depth is required. Take wildflower seeds for example. They should be strewn on the soil surface and pressed or rolled into firm contact with the soil, but not into the soil. Again, imagine you're a tiny, little seed with just enough stored energy to germinate. You want to be able to set down roots and throw up vegetative growth as easily and quickly as possible so that you can get on with things. You need sunlight to germinate and grow. If you're having to force your way up through a layer of soil to reach sunlight you're worn out by the time you get there and there's no energy reserve left for you to develop roots and leaves. A good general rule of thumb: the smaller the seed, the more shallow the planting depth.
Val Ford is a Holmes County Master Gardener. If you have a gardening question or problem, contact your local Extension Office or e-mail Val at FLSnowflake7592@aol.com
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