Haste makes waste. Jumping the gun on planting seeds in a cool spring doesn’t yield summer vegetables a day earlier than waiting until it’s warmer. It’s not just day and night temperature that makes the difference, it’s ground temperature. Most folks get all excited on the first really warm spring days, then run out and plant a garden. Inevitably this event is followed by rain, hail and frost, which decimate the seedlings and prevent some seeds from sprouting at all.
Many warm sunny days and mild nights are required to raise the top few inches of the huge damp mass of earth to average 60 to 70 degrees, the optimum required by summer vegetables seed. This soil temperature issue is often the reason why gardens don’t get off to a rocking start.
One reason soil remains very cold is because it’s saturated with water. Spring rains upon poorly drained clay soils can cause the surface layers to become soggy. This plus cold temperatures can cause the seed to rot before it ever germinates due to anaerobic (oxygen-free) saturated conditions.
You won’t recognize the delay unless you know the average days to germination for each crop printed on the seed packet. For example, tomatoes and other nightshades take roughly a week to start growing if soil is very warm. If your seeds don’t come up after two weeks, you may have a problem. Dig up a few seeds at different places to check, then possibly plant again if they’re soft and mushy or absent altogether.
Sometimes the seed manages to germinate, but the seedlings emerge just to sit there and refuse to grow much. It’s just warm enough for germination, but conditions aren’t right for the kind of rapid early development we need. Super slow seedlings are fodder for the earliest plant-eating bugs, birds and other wildlife, some which come out only at night to feed totally unseen.
In suitably warm conditions, the seedlings should fly out of the ground and reach a safe height within days so growing tips rise well above the plant eaters. This is one reason why many slow-starting vegetables are grown from seedlings started indoors, where they reach a size that’s not so easily damaged by pests.
Knowing the temperature problem can save you replanting when the average May 1 planting date is too wet, frosty or cold and should be delayed slightly. New gardeners often learn painfully that no two growing years are the same and dates are just general guidelines from which we depart on earlier or later springs. Don’t assume what you did last year works for this new one if the weather is a roller coaster.
It takes full awareness of every day’s weather and close observation of the garden itself from April to June to determine when conditions are settled enough for heat-loving summer veggies. That’s why temperature and rainfall are both linked to the start of the garden far more than calendar dates.
The second timing related task is applying mulches for the heat. A mulch (straw, compost, wood chips, etc.) lies right on top of the soil to shade it, keep it cool and greatly reduce surface evaporation. In hot and dry regions, drought, or where water conservation is important, mulches create a spa-like environment in the root zone so plants aren’t stressed by rising heat.
Don’t mulch your vegetables at planting time in the north — soil heating is encouraged so the seedlings grow. Wait until temperatures start to rise and plants are further along before you apply mulches, because that’s when they’ll need the cooler ground as a refuge. For best results, keep your mulches at least an inch clear of all stems to avoid damage and diseases.
These subtle differences in microclimate at the time we start the summer garden are tricky to learn for newbies. It’s easier if you look at it as consciousness-raising. By gradually discovering the nuances of the backyard garden this year, you begin a lifetime of mentally cataloging the very early conditions linked to good yields and bad as farmers have done for millennia.
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Maureen Gilmer is an author, horticulturist and landscape designer. Learn more at www.MoPlants.com
