Your Own Glass House: Home Greenhouse

Hockley Valley gardener Liz Knowles offers the following advice for making the most of your own greenhouse.

March 22, 2007 | | Back Issues

Our greenhouse was installed on the west side of our house over twenty years ago. I still consider it to be the best tonic for winter blahs.

Through trial and error I have learnt these lessons:

  1. The best location for a greenhouse is on the east side of a building because it warms up faster in the morning and does not get as hot in the afternoon. This has a major impact on what plants do well in the greenhouse.
  2. Buy the largest greenhouse you can afford. Even then you will find it isn’t big enough. We opted for one that was eight feet by sixteen feet; however, I could easily fill one twice the size.
  3. The type of glass – single pane or double – will also impact what grows well. We opted for double because, even though I wanted a “cool” greenhouse, it requires less heat and also is engineered to withstand the snow loads common in this area. The downside is that some plants become leggy – that is, they are not as compact as they would be growing outside.
  4. Good air circulation is critical in a greenhouse. It helps to keep the temperature even throughout. I keep a fan operating all winter.
  5. I have a small electric heater on standby, but only use it when the thermometer dips below about minus 15ºC. I maintain the temperature in the greenhouse between about 2ºC and 5ºC by keeping the door into our house ajar.
  6. The greenhouse has an automatic roof vent which opens almost daily from April to October. We recently replaced the greenhouse glass with a “high- efficiency” glass. As a result I no longer need an external shade cover on the greenhouse in the summer months.
  7. Water is the other key component. I have hot and cold faucets in the greenhouse and use tepid water. I add diluted liquid fertilizer only as plants start showing growth in the spring. If the weather is cool and overcast, I may not water for several weeks in the winter when most of the plants are dormant as they will not tolerate soggy roots. If it’s sunny, I water about once a week in fall and winter.

I use the greenhouse primarily from September to late May, I like to empty it out in summer so that I can clean the glass and also to break any disease cycles. I am careful to look over and discard any diseased plants before I put them back into the greenhouse in the fall.

I start to move in tender shrubs and perennials, succulents and the like when frost threatens in September. The hardier plants, such as rosemary and phormiums, which can take some frost, do not come inside until mid to late November. Dahlias, arisaemas and other “tender” bulbs store well in bushel baskets or paper bags in semi-dark conditions under one of the benches. It’s amazing how many plants fit into a relatively small greenhouse, I tier them up in layers in places and put the shrubs onto inverted plant pots to allow more room on the bench. Like a garden, my greenhouse has cold spots, so I make sure the more tender plants are kept in the warmer parts.

In spring, I start to acclimatize the hardiest shrubs and perennials outside as the weather warms up in April. If a frost threatens I pop them back inside overnight. Any vacant space is taken up by this year’s seedlings as they are potted into bigger containers. After the risk of frost is over towards the end of May, everything is moved outside.

I have a heated propagating box, kept at 21ºC, into which I put cuttings in the fall and spring. By mid-March I also have trays of annual, perennial and vegetable seeds waiting to germinate.

I start tomatoes, peppers, eggplants, squash, cucumbers and lettuce inside. The latter has been particularly successful. I seed new pots of lettuce every two to three weeks from March to August and the seedlings are transplanted into the garden under floating row covers. For the past few years we have enjoyed garden lettuce from late May to Christmas.

About the Author More by Liz Knowles

Liz Knowles has been gardening in the Hockley Valley for more than 25 years.

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