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Shane Smith is this week's guest writer.  Even though Shane talks about selecting the right plants for use in a greenhouse, his information benefits all gardeners, whether indoors or out.  Shane Smith appeared on GardenSMART'S episodes 25 and 26.  This is an excerpt from his book Greenhouse Gardener's Companion, �2000 & 2009.  All rights reserved. Reprinted at GardenSMART.TV web site by permission from the author.

---Anne K Moore---



by Shane Smith, Director of the Cheyenne Botanic Gardens

GardenSMART Episode 25 2009

GardenSMART Episode 26 2009

Selection for Fruit and Vegetable Shape and Size

When a plant grows vertically, it can make better use of unused air space. If you are growing vegetables or flowers, vertical growing might mean more of both for you to enjoy. Because the growing space in a greenhouse always seems to be limited, it is sometimes wise to grow vining or vertically growing varieties as opposed to bushy varieties. When it comes to vegetables, there are many types that grow both bushy and low, or tall and vining. These include peas, beans, cucumber, squash, melons, figs and bananas. Tomatoes are also included in this list, but horticulturists have a special vocabulary for them that might pose some confusion. Bushy tomatoes are called determinate because they grow to a determined height and then the main leader on the plant quits growing. Tomatoes that grow tall and viney are called indeterminate. That is because they can grow indeterminately, given the right growing conditions.

Bushy vegetable varieties can fit into special places in the greenhouse or sunroom, like next to a knee-wall with little headroom. But, one of the best places to use bushy varieties is in pots. The tall vining varieties grown in a pot might quickly get out of balance, with too much top supported by a small, limited root system. This will cause the plant to wilt at the slightest provocation. It will also be under constant stress, which is an invitation to every bug and disease in the area. This type of plant stress can be avoided—just make sure that the pot or container corresponds to the size of the mature plant. Grow the big indeterminate tomatoes in tubs or beds.

I have had great luck growing bush beans in hanging baskets. I like to grow bushy determinate tomatoes in 1- to 5-gallon (3.8- to 19-liter) pots and have had decent yields. Play around with bushy vegetable varieties in pots, and you�ll see that it works great.

Selection for Disease Resistance

The inherent high humidity of greenhouses and intensive plant production can bring conditions that promote plant diseases. Diseases are rarely controlled with chemicals and are not recommended. The best defense against disease is to maintain healthy plant growth. But you can also help things out by selecting varieties that show some tolerance or resistance to a particular disease problem. This is where you need to really study the seed catalogs and look for any listed "resistance to disease." Before you start, it is important to make every effort to identify your disease problem. There are many good books and web sites on plant diseases as well as good resources through your local university. Your county agricultural extension agent can also be helpful in identifying a particular disease problem.

Many plants show variability in their resistance to diseases. For instance, I had a problem with powdery mildew affecting squash and cucumbers. Powdery mildew is a white powdery fungus growth that covers the leaves and slows growth. I went back to the catalogs and found varieties that were listed as resistant to powdery mildew. By just changing varieties, I was able to see about an 80 percent reduction in the disease without doing anything else to control the mildew.

What the catalogs won't tell you is that even though a plant may be listed as resistant, that degree of resistance may vary a good deal, from totally resistant to only slightly more resistant. Don't be surprised if you are growing a variety that is listed as "resistant" to a certain disease and still see evidence of the disease. The variety may be only more tolerant than other varieties.

You may discover that some varieties have some resistance to a disease, even though it is not listed as such in the catalogs. For this reason, don't put all your eggs in one basket. Try to grow more than one variety of a particular crop, and nature's genetic diversity will work for you. Then with a little experience under your belt, you will have identified superior varieties. Good record keeping is helpful in determining what worked well and what was mediocre. Don't be lazy about being a good observer and take the time to make a few notes. It's not hard and the reward? Having healthy, productive plants. Sometimes you have to figure things yourself as this valuable information not available anywhere else.

Selection for Insect Pest Resistance

Plant varieties that exhibit resistance to insect pests are rarer than those resistant to disease. Breeding plants for insect resistance seems to be harder to do. The better catalogs will occasionally mention some resistance to bugs, but usually you have to learn on your own, as some plants are naturally more resistant to bug attacks.

A good example of selecting for pest resistance happened to me with lettuce. I used to grow a light green Grand Rapids lettuce variety called "Slo Bolt." It was a good producer in winter, spring and fall but it was readily attacked by both aphids and white fly. Then I switched varieties to two newer, related lettuces: Green Ice and Royal Green. The major difference was in the color of the leaf. Instead of having light green leaves these were decidedly darker green in color. I found that the bugs were much less attracted to the darker green lettuce varieties. For some reason the bugs just loved the color of the lighter green plants. This simple change in varieties made a huge difference in my bug problem.

Don't expect that just by changing varieties, you will totally eliminate a bug problem. It can help. Again, keep records. There may be other reasons for a crop's insect tolerance besides just the color of the leaf. Be observant. Watch the changes year to year among the varieties to be sure a change in bug infestation is truly because of a change in varieties and not because it might have been a bad year for bugs (yes, bugs can have good years and bad years).

Visit again next week for more information on choosing varieties for the home greenhouse and for growing in the cold months indoors. HOME GREENHOUSE GROWING for the HOME GARDENER, Part 2, next week at

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

---Posted November 13, 2009---


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