How to Grow Greenhouse Tomatoes in Winter

Updated November 21, 2016

Few things outshine the flavour of juicy home-grown tomatoes. For many, this summer time treat is the epitome of garden-fresh goodness. The arrival of winter does not have to spell the end of fresh tomatoes. If you're lucky enough to own a greenhouse, the tomato growing season can be extended indefinitely. Although tomatoes can be a tad fussy when grown indoors, with practice and patience you'll soon be able produce an ample supply of tasty tomatoes all year long.

Purchase tomato seeds developed specifically for greenhouse growing conditions. Alternatively, consider planting cherry or salad tomatoes as they are well suited to life in containers.

Clear a table or bench for the plants. Ideally, the tomatoes should be placed in direct sunlight, approximately 36 inches above the ground. Remember heat rises and tomatoes are a heat-loving plant.

Spread a 6 to 8 inch layer of bark mulch beneath the table that will hold the tomatoes and water the bark thoroughly. Water the mulch once a week throughout the winter. As the wood decomposes, it will emit heat which will help to stabilise the temperature inside the greenhouse.

Make a soil mixture by combining two parts commercial potting soil with one part compost. Mix the two until they are thoroughly blended and then add water until the medium is evenly moist.

Scoop the planting medium into seed trays or small cups and then plant the tomato seeds, placing them 1/4 inch beneath the potting soil. Cover the seeds lightly with soil and add water. Keep the planting medium moist until the seeds germinate, adding water daily or as needed.

Cover the seeds with a sheet of plastic cling film as this will help to retain both moisture and heat. Place the newly planted seeds in the sun. According to the University of Kentucky Extension office, tomato seeds germinate when the soil around them reaches 26.7 degrees Celsius. If additional heat is needed, consider placing a fluorescent light directly over the seeds and leaving it lit for up to eight hours per day.

Remove the plastic film when the seeds begin to sprout and place a fluorescent light or grow light 5 to 6 inches above the seedlings. Keep the lights turned on 16 to 18 hours per day.

Transplant the seedlings to 3-gallon pots when they have developed two sets of true leaves. Use one container for each tomato plant. Fill each pot with planting medium and gently transfer the tomato plants to their new homes.

Align the planters in a neat row and place a three-fluorescent-light strip overhead. Set the light fixture 2 feet above the plants. Turn the lights on and double check to be sure all the plants are positioned within the scope of the light fixture. Rearrange as needed.

Check the plants each day adding water as needed to keep the planting medium from drying out. Once each week add all-purpose water-soluble plant fertiliser to each pot. Sprinkle 1/4 cup plant food around the base of each tomato plant and add water -- this activates the chemicals in the fertiliser and carries the nutrients to the plant's roots.

Shake the plants gently once they begin to flower. Every day, grasp the tomato plant by the base and give it a soft jiggle. This will release the pollen from the blossoms and lead to the development of fruit.

Monitor the temperature in the greenhouse closely. To ensure maximum tomato production, keep the temperature above 60 but below 32.2 degrees Celsius. Cover the greenhouse with blankets overnight if necessary to help the structure retain heat. Remove the wrappings in the morning to make use of the natural heat provided by the sun.


You can also grow tomatoes indoors in a sunny window.

Things You'll Need

  • Tomato seeds
  • Bark mulch
  • Potting soil
  • Compost
  • Seed trays
  • Plastic cling film
  • Fluorescent lights
  • 3 gallon containers
  • All-purpose fertiliser
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About the Author

Lisa Parris is a writer and former features editor of "The Caldwell County News." Her work has also appeared in the "Journal of Comparative Parasitology," "The Monterey County Herald" and "The Richmond Daily News." In 2012, Parris was honored with awards from the Missouri Press Association for best feature story, best feature series and best humor series.