Irrigation for a Small Greenhouse

Another rainy day project in the garden!

Several years ago, with the help of a friend, I installed a greenhouse in a corner of my garden. This is a typical backyard structure, just ten-by-twelve feet, not an expansive “plant factory” like those on the annual open greenhouse event hosted by local nurseries for mostly flowers.


My greenhouse, although small, has ample bench and shelf space for an ambitious program of propagating and maintaining plants. Plants will assume the primary role of growing, and a greenhouse can easily exclude deer and gophers, but operating a greenhouse still requires investments of the gardener’s time for planning, planting, monitoring and controlling climate, diseases and the smaller pests.

Best intentions aside, other priorities can leave the greenhouse unattended. When that has happened to me, my plants have tended to expire.

In addition, my greenhouse developed another problem. I had installed a sprinkling and misting system to irrigate the plants, using an inexpensive battery-operated timer. It worked fine until the battery died when the irrigation valves were open. The timer did not have the power to close the valves, so they ran for days, unobserved. This resulted in soggy plants, a huge water bill and attendance in a water conservation workshop.

I turned off the system in favor of watering by hand, but because the greenhouse is away from the house, it was easy for me to neglect the watering schedule. Except for some succulents, my plants did not do well under that plan. A clear need existed for a reliable automatic irrigation system.

Working with another gardening friend, we are installing such a system, with the longer-term objective of starting seeds, growing new plants to garden-ready size, and maintaining surplus plants for giving to other gardeners. (I could also grow plants for sale, but the small-scale nursery business would seem uneconomic.)

The irrigation system includes a professional grade controller, capable of scheduling four irrigation valves, and two valves plus capped connections for two future valves. Wires running the length of the greenhouse support flexible tubing over plants, which will be on tables or shelves (not on the ground). The tubing will have multiple emitters that will either spray or drip water on the plants. Spray is best for groups of seedlings or small plants while drip is more effective for larger plants.

Some gardening friends use their greenhouses to maintain collections of succulent plants that require warm, dry conditions, or orchids or other tropicals that require warm and moist conditions. Greenhouses in public gardens often focus on one or the other of these plant groups.

When planning a greenhouse for the home garden, a good first step would be to decide which plants are to be grown, and what climate those plants will need: cool/moderate/warm, or dry/tropical. To learn about these options, search the Internet for “types of greenhouses.”

My greenhouse is intended to moderate temperatures, year-round, and to control moisture levels through scheduled spray and drip irrigation. This growing environment will support a wide range of plants, excluding only those that require extreme conditions. Plants that require a winter chill, for example, grow poorly in the coastal Monterey Bay area, whether in a greenhouse or in the ground.

The home gardener can use a greenhouse to extend the growing season, protect against larger pests, and control the environment for either specialty plants or general gardening. Greenhouse management can be an engaging and satisfying form of gardening; it can also be more expensive and time-consuming than conventional gardening. Enter with eyes wide open.


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