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17979 State Route 536
Mt. Vernon, WA 98273
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March in Your Greenhouse
March in Your Greenhouse
By Carol Yaw
On the West coast, where I live, and many other parts of the U.S. with spring weather arriving, you can start a vast range of plants this month if you keep your night temperature at 45° F or above.

(In colder areas where you still have snow, maintain a minimum temperature of 35° to 40° F to keep your plants from freezing until spring starts to arrive.)

 Growing Fun for March
  1. Continue to sow annuals and half hardy annuals, bedding plants, and basil for mid to late summer. See pot paks and flats.

  2. Repot orchids and other perennials that are root bound.

  3. Bring in tuberous begonias and place in trays of peat. Pot up as their leaves start to appear.

  4. Put dahlia tubers in a damp peat/sand mixture and let buds form. Next, cut the roots into pieces. Each piece needs a minimum of one tuber and one shoot at the top. Plant in rich compost.

  5. Flowering chrysanthemums in 3-1/2" pots started earlier should be ready to repot into 5" to 6" pots by late March. Once established, harden them off in a cold frame before planting outside for summer blooming.
See our Deep Pots 
  1. Sow winter flowering plants like gloxinia, cyclamen and cinneria.

  2. Transplant seeds sown earlier when their first pair of true leaves start to show.

  3. Strawberries and Melons: As buds appear on fruit, start to fertilize. If you are growing fruit that requires pollination, refrain from damping down your greenhouse when the flowers open up as it may prevent the fruit from forming. When the fruit has set, you can resume damping down again.

  4. Harvest any salad greens, radish, mushrooms, cress, chicory, etc. that are ready and re-seed them.
  1. Sow summer cabbage, lettuces, eggplants, peppers, leeks and most herbs in pots to transplant outside later.

  2. Sow beans and place containers on a a heat mat for best germination results. Beans are a dependable crop year around in the greenhouse if it is heated. Trellised pole beans make the best use of space and produce over a longer length of time. Bush beans grow well in containers and don't require trellising. Use a legume inoculant in the soil when you transplant them into the ground or pots. Keep them in a sunny spot.
  1. Transplant tomato seedlings planted in February into 3" pots. If you didn't already start them, sow tomato seed in a propagator for planting in a cool greenhouse in early May or outdoors later. See Growing tomatoes in your Greenhouse.
  1. Sow cucumber seed in a propagator for planting in a heated greenhouse in April.

  2. Pinch out growing points of fuchsias and geraniums to increase their bushiness.
  1. Prepare hanging baskets for outdoors later. See Hanging Baskets for your Greenhouse.


Give increased attention to ventilation and watering this month.  

On bright sunny days, the greenhouse will start to heat up quickly and then cool down just as rapidly as the sun disappears. Try to modify wide temperature fluctuations, keeping the temperature as even as possible in the 45° F - 65° F range. On sunny days, open the roof and side vents, and the door midday if you do not have them automated. Be sure to close up your greenhouse before the outdoor temperature starts to fall.

Use FREE heat from the sun to power your solar Vent Openers.
  "I love my greenhouse I spend many peaceful hours starting seeds, transplanting, repotting … and my beautiful yard reaps the benefits!"
                               Tee Davis Overby
                               Oak Harbor, WA


Damp down the greenhouse floor on warmer days with a garden hose to cool it off and provide extra humidity.

Increase watering and fertilizing of established plants that are showing active new growth. Watch closely that seed starts and seedlings do not dry out. Water and mist as needed.

Our 25 ft. 3/8" Coiled Hose stretches out easily then coils back up automatically

Our 25 ft. 7/16" Ultra-Light Slim Hose half the size and weight of a regular garden hose

Charley's Greenhouse Wand lets you water quickly without harming your seedlings



If you are only using your greenhouse to start seeds and seedlings, you do not need to warm up the entire greenhouse. For now you only need a soil warming mat or soil cable under your seeds to maintain constant, gentle heat they'll need to develop healthy roots.
I recommend, however, that you use a moisture-resistant heater with an accurate thermostat for night protection in case of an unexpected freeze or late cold spell. Set the automatic thermostat control to cycle on at 45° F for a cool greenhouse.


You may need to cover part of your glazing this month or next with shade fabric.

Your new seedlings will need some partial shade from intense noon sun.

Place your shade-loving plants under the benches or in other shady micro-climates.

 Pest Control

Late March through September is when harmful insects and other pests can create challenges. Take preventative measures now!
Keep an eye out for whitefly, aphids and red spider mites in particular. My best arsenal of pest controls for the greenhouse include:
Better yet, consider adding some beneficial insects to your greenhouse to discourage any stray, harmful insects or other pests before they multiply. Green lacewings, aphid midges, ladybugs and many others are great fun to watch and very effective if released early. See Beneficial Insects for more details.
Damp-off is a seedling disease caused by contaminated soil. When starting seeds, use a sterile seed-starting medium to prevent pest and disease problems. Over-planting too thickly can also cause damp-off.

Sterilize all containers, trays and potting utensils you are reusing with a
Typical symptoms of damping-off are rotting
stems at or near the
soil line.
Between seed starting, watering, transplanting and general maintenance, the greenhouse is a bustling place in March. Don't forget to make time to connect with the joys of greenhouse gardening -
  • Take a deep breath of the warm, humid air.
  • Marvel at how fast your seedlings are growing daily.
  • Take in the sweet smell of your winter jasmine or other fragrant plants in bloom.
  • Discover the new healthy growth on plants that you wintered over from outdoors.
alias Mrs. Charley

- Check out all of Charley's greenhouse models.
- Watch Greenhouse 101 - 19 short video clips
P.S. - Need some more growing space? See our benches & shelves.