Black magic plastic

A layer of plastic film helps soil warm up to spring plantings
By L.A. Jackson
Black magic plastic

The sooner the soil warms up, the sooner annuals such as zinnias will have their day in the sun.

Ready to plant your garden? Not so fast. . .

Even with North Carolina’s temperatures approaching short-sleeve weather, dirt is denser than air, meaning it takes soil much longer to warm up in the springtime. So if you want to plant heat-loving summer annual vegetables and ornamentals early in the growing season, plastic will help start them sooner.

A layer of plastic film covering garden ground will act much like a greenhouse by absorbing heat from the sun during the day and preventing its loss at night. Black plastic does a good job of warming the soil and, because it blocks light, also discourages weeds. 

After you have turned over the garden’s soil for spring plantings — and added fertilizer — cover it with a single layer of the plastic, burying the corners in dirt. Poke small holes in the plastic to allow rain to drain into the earth. Rain will not only water the garden, but, by way of the droplets, the mild temperatures from the early spring showers will reach deep into the soil, warming it further.

Give the plastic two weeks or more to raise the soil’s temperature. Then, cut 4-inch wide X’s into the film and set your plantlets into the dirt underneath.

By the middle to end of May, the plastic will have done its job in starting young plants off early, and the additional heat generated by the film won’t be necessary — nor welcomed — during the hot summer months. Rather than removing it, simply poke more holes in the plastic to allow air and moisture to pass freely through, and pile a few inches of organic mulch such as dried leaves, hay or compost on top. Organic mulch will prevent the soil from becoming too hot, inorganic plastic sheets will stop weeds, and both will help conserve moisture.

At the end of the growing season, while clearing out spent annuals, simply pull the sheets up, toss the plastic away, and at least tip your hat as a way of saying, “Thanks!” to this handy garden helper.

Garden To Do’s

  • ’Tis time to fertilize. In particular, established roses, shrubs, perennials and trees will benefit from a wake-up jolt of nutrients early in the month. To minimize this job for the rest of the growing season, use a time-release fertilizer that will slowly send nutrients into the root zone over the next several months.
  • As the flowers of naturalizing bulbs such as crocus, daffodils, hyacinths, ipheion and species tulips begin to fade, allow the foliage to turn brown before pruning it back. While the leaves are green, they continue to absorb energy for next year’s flower show.
  • Now is a good time to divide and transplant perennials such as asters, bleeding hearts, astilbes, ajuga, oxalis, coral bells, phlox, hostas, liriope, daylilies and shasta daisies.
  • How about more mint, creeping thyme, tarragon and chives? These herbal helpers can be divided at this time, too.
  • If you are preparing garden trellises for annual ornamental and vegetable vine plants this summer, why not add more color and interest to the structures? Sure, regular white string will work as supports for the vines, but so will the colorful yarns that can be found at craft stores.
  • Time to wake up the veggie patch. At the beginning of this month, get growing with the plants and seeds of such cool-season vegetables as lettuce, kale, onions, spinach, potatoes, cabbage, sugar snaps and radishes. Also, the middle of the month is prime planting time for beets, broccoli, cauliflower and Chinese cabbage.
  • Planning on putting up birdhouses this spring? Just remember to buy or build birdhouses made of wood. Compared to metal or plastic, wood is a better insulator and helps prevent the feathered occupants from overheating during the sizzling days of summer.

About the Author

L.A. Jackson is the former editor of Carolina Gardener Magazine. If you would like to ask him a question about your garden, contact L.A. at: lajackson1@gmail.com

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