Vermont Vegetable and Berry News – November 21, 2007
Compiled by Vern Grubinger, University of Vermont Extension
(802) 257-7967 ext.13,

Adapted from an article by Liz Maynard and Dan Egel, Purdue Extension

Greenhouse heaters may produce combustion by-products that cause plant damage. One common by-product is ethylene. Perhaps the most sensitive vegetable to ethylene is the tomato plant. Ethylene concentrations sufficiently high to cause plant damage can result from heaters that are burning dirty (incomplete combustion), cracks or leaks in the heater block, inadequate air supply to the heater, and heater exhaust getting back into the greenhouse. (Ethylene can also be produced by decaying plant parts and ripening fruit in relatively small amounts.) Symptoms of ethylene damage include downward growth of leaves (epinasty), leaf drop and fading flowers.

We recently observed ethylene damage in a greenhouse where the heaters were malfunctioning (the heaters were set up for natural gas when they should have been set up for LP). The key symptom was poor growth of tomato seedlings. A portable gas detector was used to measure ethylene concentrations of 1 to 5 ppm (parts per million). Ethylene damage has been reported at as low as 100 ppb (parts per billion). It is likely that ethylene was present in the greenhouse over a period of several days. Damage caused by ethylene is influenced by both the concentration and period of time plants have been exposed to ethylene. In addition, some plants are more sensitive to ethylene than others.

To avoid damage from ethylene and other air pollutants:

• Have heaters checked by a professional; follow maintenance recommendations.
• Assure adequate air supply for complete combustion. For each 2500 BTU’s of heater output, 1 square inch of vent cross section is needed.
•  Prevent back drafts. Make sure the chimney extends 2 feet above the ridge of the greenhouse, or 2 feet above a 10-foot line to any part of the structure.
• Install an inexpensive carbon monoxide detector. If carbon monoxide levels rise it’s likely ethylene and other pollutants are present also. And if carbon monoxide levels    are high it is a significant human health hazard.
• Scout for growth effects of ethylene; investigate right away if you see anything.

For more info: “Reduce Air Pollution from Your Heating System” by John Bartok, at: or call me for a copy.

(compiled by Wendy Sue Harper, NOFA-VT)

The onset of cooler weather and shorter days in fall brings about changes toward dormancy in some plants and a physiological toughening. The resistance to cold develops in a number of steps. Toward the end of the growing season, the rate of growth in plants slows down leading to the accumulation of carbohydrates in the leaves, because they are not needed for growth and respiration. These carbohydrates are translocated to other parts of the plant, especially the roots. Also water dynamics change in the plant. The plants protoplasm has a higher proportion of water bound to proteins and a higher concentration of colloidal and dissolved materials as weather cools in fall. All these materials act as plant-cellular antifreeze, which protects the plant. Waxy leaves on some plants also provide some protection from cold.

Many plants are adapted to cold weather because they evolved in cool climates. Cultivated beets, and thus Swiss chard, are thought to be derived from the wild beet of Northern Europe. While kale, collards and mustards have an ancestral cabbage in common that was grown 8000 years ago in the low coastal areas of northern Europe, before they were brought to the Mediterranean and Asia.

(adapted from USDA-Agricultural Research Service)

The pigments found in plants play important roles in plant metabolism and visual attraction in nature. They are also important for humans, attracting our attention and providing us with nutrients. Major plant pigments include carotenoids, anthocyanins and other flavonoids, betalains, and chlorophylls.

Chlorophylls, which are green, and carotenoids, which are yellow, orange, or red, play pivotal roles in photosynthesis. They occur in all green plants. Chlorophylls capture light energy and convert it into chemical energy. Carotenoids protect the chlorophylls from photo-oxidation and are accessory, light-harvesting pigments. They occur in all green tissues as well as independently of chlorophyll in flowers (where they serve to attract animals), storage organs, and other plant parts. Flavonoids include red or blue anthocyanins and some white or pale yellow compounds. Flavonoids in flowers and fruit provide visual cues for animal pollinators and seed dispersers to locate their target.

Approximately 40 carotenoids have been found to be vitamin A precursors. When these are consumed, they are enzymatically broken down to retinol (vitamin A). In this way, consumption of horticultural crops provides over 80% of the vitamin A for the world. Vitamin A deficiency worldwide is the most common specific dietary deficiency as it afflicts millions of children each year with blindness, or death. Subclinical deficiency reduces immune function thus increases the risk of severe and fatal infections.

Research findings since the 1970s have indicated that food crops containing carotenoids, anthocyanins, and other flavonoids are believed to function as "chemopreventers", by providing protection against certain forms of cancer and a reduction of cardiovascular disease. Interestingly, non-provitamin A carotenoids such as lycopene, the major pigment of tomato and watermelon also confer chemoprevention. The important characteristic common to all chemopreventers is their antioxidant capacity. The antioxidant properties of carotenoids which protect plants in photosynthesis apparently may also protect humans from carcinogens and heart disease.


Some new sections have been added or updated on this web site including: Budgets, Energy on the Farm, Food Safety and Processing, and Crop by Crop Production. The latter has links to the best detailed production fact sheets and guides I could find.  My goal is to provide practical, credible information for commercial growers. I welcome your feedback and as always, please let me know if you come across a broken link or if you know of a resource that should be added.

(contact me for resources to help with these)

• Have Saturated Media analysis done on greenhouse soil/potting mix.
• Write an Employee Handbook for your farm.
• Complete your Farm Business Plan.
• Complete and compare Enterprise Budgets for your major crops.
• Write your SPCC (spill prevention) plan if you have a lot of stored fuel.
• Attend at least one Grower’s Conference to get new ideas for next season.

UPCOMING MEETINGS (for details on these and links to other educational events see:; click on ‘meetings and events’)

Nov. 27.  Forging the Farm-to-Cafeteria Link, Green Mountain College, Poultney VT, from 4-8 pm.
Contact Rutland Area Food and Farm Link at (802) 287-9311

Dec. 1. Honey Bee Health for Beekeepers and Farmers. With USDA Researcher Dr. Judy Chen. Goffstown NH.
George Hamilton (603)641-6060 or

Dec. 3-4.  Renewable Fuel On-Farm: Canola, Biodiesel, and Corn. Bangor ME.
Peter Sexton at (207)764-3361 or

Dec. 10. Diagnosis and Management of Nematodes in Vegetables. Manchester NH.
Beth Gugino at (315) 787-2412 or

Dec.11-13. New England Vegetable and Fruit Conference and Trade Show. Manchester NH. or call me for a brochure (802) 257-7967 x13.