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An excerpt from his book
“Greenhouse Gardener’s Companion”
All rights reserved.
Reprinted at GardenSmart TV web site by permission from the author.


by Shane Smith, Director of the Cheyenne Botanic Gardens

GardenSMART Episodes - Show 25, Show 26, 2009

Greenhouse Varieties             NOTE:  This is a continuation of last week’s article.

There have been many vegetable and flower varieties developed especially for commercial greenhouses that sometimes are offered in regular retail seed catalogs. These greenhouse varieties were selected mostly for the commercial greenhouse grower in mind. They have been chosen for high productivity under ideal conditions of light and temperatures in a totally controlled ­energy-intensive environment. These varieties usually have the characteristics of disease resistance, high yields, vining growth, bolt resistance (lettuce) and resistance to physiological disorders (i.e., fruit cracking on tomatoes). In the case of cucumbers, some varieties are labor saving because they don't require any hand pollination in order to set fruit.

In better seed catalogs, these varieties are usually flagged with a statement such as ''For greenhouse production'' or ''For forcing.'' Forcing is a common European horticultural term used to describe the forced growing of the plant out of its normal season. I always thought it was a term that sounded like a Nazi greenhouse operation ''vee have vays to force you to grow''

Two catalogs that commonly list greenhouse varieties are Stokes and Johnny's Selected Seeds. When you are reading these catalogs, you could find the perfect home greenhouse cucumber (sometimes called a European Forcing Cucumber) that does well in ''cooler temperatures and is tolerant to powdery mildew.'' Here is where you apply what you know about your greenhouse environment and your greenhouse's specific problems with diseases in order to select the right variety.

Another way to find varieties bred for greenhouse conditions is through your local commercial greenhouse grower. They might let you thumb through their wholesale catalogs that only commercial growers use. See if you can buy some seed through a local commercial greenhouse grower. Greenhouse varieties are not available for everything, as you will find only a limited number of crops. I hope that in the future, people will show the seed companies that there is a large demand for these varieties. Maybe then, they’ll start breeding a whole slew of crops specifically for the home greenhouse and even the solar-greenhouse environment.

Here are seeds and plants that have been developed for greenhouse growing- Vegetables: certain herbs, carrots, cucumber, lettuce, peppers and tomatoes. Flowers: Alstroemeria, aster, calceolaria, carnation, chrysanthemum, cineraria, cyclamen, freesia, gerbera, ranunculus, rose, snapdragon and stock.

Crops That Need Winter

Why not grow native wildflowers, asparagus, rhubarb, cherries, apples, peaches, pears, apricots, ­currants or raspberries in your greenhouse? The main reason that these crops are difficult is that they are temperate crops used to an environment where the cold of winter is not only expected but also required for natural growth. Without the winter cold treatment, they would not produce properly. In addition, these crops require an appreciable amount of greenhouse space, but produce for only a relatively short time. In addition, depending on where you live, these crops may do just fine outside and, unfortunately, won't do much better inside unless you live where summer frosts are common.

Still, there are those who would be in total heaven if only they could be eating fresh, homegrown rhubarb or peaches in the winter. Well, with some effort there are ways to pull it off, although I'm not sure if it is worth the effort. All you have to do is fool Mother Nature (which is not always nice). You do this by faking a winter, or as horticulturists put it, 'force' a crop.

Different crops and varieties have different chill requirements, and these can be imitated artificially. One way to provide the proper amount of winter cooling is to go outside in midwinter or early spring, carefully dig up the desired plants (you may need a pick for the frozen soil) and transplant them inside for late-winter harvests. I call this the 'half-winter' treatment, which is usually enough to ensure proper production. Wintertime transplanting can be close to impossible with an 8-foot (2.4-meter) peach tree, but with dwarf varieties in moveable containers on rollers, it could be done more easily.

Growing of these winter-loving temperate crops in a greenhouse warrants some further experimentation and development. There is some good potential for growing crops such as asparagus and rhubarb in winter greenhouses. In the South, plant breeders have actually developed varieties of temperate crops that require less chilling in order to produce yields. If you want to pursue this begin looking through the many available regional, southern U.S. plant catalogs and you will occasionally find a low-chill requirement plant.

Vive la Diff'rence

As you gain more experience in the greenhouse, you will find it is rare for the same fruit or vegetable variety that you grew successfully outside to also do equally well inside. The climate in a greenhouse is different and we need to approach it with that in mind. The extra yields of vegetables and flowers make the reward well worth selecting plants especially suited to the greenhouse environment.

The inside garden and the outside garden are two different and special worlds and for the most part should be treated as such. It is not more difficult or complicated to grow under glass. It is simply different.

Visit for more greenhouse resources, garden tips, and to order the book, 'Greenhouse Gardener's Companion'.

---Posted November 20, 2009---

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