Vermont Vegetable and Berry News – December 1, 2005
Compiled by Vern Grubinger
University of Vermont Extension
(802) 257-7967 ext.13


All commercial growers in Vermont should have received this simple one-page form. If you have not done so, please fill it out and return in the pre-paid envelope asap. Thanks.

(from John Bartok, Univ. of Connecticut Extension)

Check Thermostat Accuracy. Mechanical thermostats tend to loose accuracy over time. You can easily check the accuracy of a thermostat. Start by checking the accuracy of a good thermometer by inserting it into an ice bath. The reading should be 32ºF. After allowing it to come back up to room temperature, place it next to the thermostat you want to check. Slowly move the dial until the heater turns on. The reading should be the same as the thermometer reading. If not, mark the thermostat accordingly. Next time the heating system is serviced, have the service person recalibrate it. If the thermostat setpoint is 1 degree F too high, a 30’ x 100’ double poly covered hoophouse will use an additional $300 of fuel for the heating season. This is based on maintaining 60 degrees F inside where the average winter temperature is 25 degrees F outside with fuel oil at $2.00/gallon, natural gas at $1.37/therm or propane at $1.17/gallon.

Sidewall insulation.  One factor that influences heat loss from a greenhouse is the amount of glazed area. In a 30’ wide hoophouse, the glazed area from the ground to bench height is about 15% of the total surface area. Insulating this area with an inch or two of polyurethane or polystyrene can reduce total heat loss over 10%. Use a closed cell insulation board and not beadboard as this absorbs moisture reducing its insulating value.

Reduce Air Leaks. In some greenhouses, cold air infiltration adds considerable to the cost of heating. Cracks around doors, vents and shutters that don’t close tight, broken glass and tears in the plastic are typical examples. For example, a 4 foot square shutter that fails to close fully and leaves 1/2 inch gaps will allow about 12,000 cubic feet of cold air to enter each hour. To heat this amount of air over a 24 hour period to 60 degrees F when the outside temperature is 0 degrees F require almost 4 gallons of fuel oil. Most infiltration leaks can be corrected with minimal cost. Weather-stripping and foam insulation work well on small gaps. Shutters not needed for cooling should be covered with a sheet of film plastic or one inch of polystyrene or polyurethane insulation board. A few hours spent in tightening your greenhouses are well worth the effort.

(adapted from Gary Pavlis, Rutgers Univ. Extension, Blueberry Bulletin)

Pruning continues to be little understood and poorly executed throughout the industry. Proper pruning is very important. It costs money, but it will cost a grower more if it isn't done, or if it isn't done correctly.

Recent research revealed that young canes are more efficient fruit producers than old canes. Canes which are three to ten years old allocate over 50% of applied water and fertilizer to fruit production but by the time a cane reaches 20 years of age, only 25% is allocated to fruit (water and fertilizer cost the grower money, and there is no profit in the production of blueberry leaves!). Additional research compared the impact of three pruning types on yield and fruit size. Plants were: 1) regularly pruned in a moderate manner such that one out of every six canes was cut out; 2) heavily pruned by removing 40% of all canes every five years; 3) not pruned at all. The result was that the regular moderate pruning resulted in the highest yield on the least number of canes. Research has also shown that as pruning increases, new cane production increases.

It is important to understand how a blueberry plant grows. Each year, canes are initiated from the base of the plant. Each succeeding year, the cane produces laterals; laterals produce laterals, and so on. Each year the lateral production on any individual cane decreases in diameter, in other words, the wood becomes progressively twiggy. As wood becomes smaller, fruit size decreases. This is why detail pruning increases fruit size.

There are 5 basic steps to keep in mind when approaching a bush to be pruned: Assess the plant’s overall vigor: is cane production adequate? Prune out all dead wood. Locate the oldest canes and prune out one of every six canes. Prune out all the low branches that will never be picked and are a source for disease. Detail prune: remove as much twiggy wood as time allows.

Armed with these basics, here’s how you deal with the different plant situations that arise. First, pruning young plantings has the primary objective of establishing the plant to obtain full production as soon as possible. During the first two years the goal is to remove flower buds, by rubbing off flower buds. However, in a big operation it is usually less labor intensive to cut the top three to five inches off each cane, which will remove most flower buds. Any weak twiggy growth should also be removed.

In year three, a small crop is possible without stunting the plant. Usually one to two pints per bush is the optimum and fruit should only be on strong wood. The fourth and fifth year twiggy growth must again be removed, as well as any lateral canes that have developed. Fruit production can be increased, but the amount is dependent on the number of new canes which were produced the preceding years: three to five canes per year is optimum. The blueberry planting should be in full production by the sixth year, though many variables will influence this; the most important are proper soil pH and nutrition, water management, and the crop-to-cane production balance.

There is not a specific pruning strategy for each variety, though a variety may fall into one of the following categories most of the time. For example, Blueray often has a spreading or open habit in which canes tend to bend down to the ground. Plants of this type must be thinned according to the one out of six rule. However, canes that are bent over also tend to produce an upright shoot. These canes should be pruned just above this upright shoot to produce a more erect plant. Other varieties that often fit into this category are Berkeley, Bluetta, Coville, Weymouth and Patriot.

Bluecrop, Collins, Darrow, Earliblue, Herbert, Jersey, Lateblue and Elliot often fall into the erect plant category. These plants become overly dense in the center, which decreases fruit bud initiation. The pruning strategy for this category is to remove older central canes before all others.

When plants are overly vigorous, the primary strategy is to remove entire canes rather than spend time on detail pruning. Varieties prone to this situation are Earliblue, Blueray, Herbert and Collins, though any variety can potentially be overly vigorous. Weak plants are treated in the opposite manner. The primary procedure is to detail prune rather than to eliminate whole canes. Varieties classically in this category are Weymouth and Bluetta.

The question of how to prune a field which has been neglected for a long time and needs to be rejuvenated often comes up when a grower has purchased such a field. The most important step is to inspect the plants and pull out any plant showing virus symptoms. The inspection must be done during the growing season because symptoms are most easily seen on the leaves. The next step is to completely prune everything down to the ground (a chain saw is the quickest and easiest method). This is best done in late winter. An application of a 10-10-10 fertilizer should be made in early April, usually at 400 lb per acre. No crop will be harvested that year. The following winter the canes should be thinned to approximately 12 to 16 per plant. A full crop can be harvested that year.

In summary, pruning correctly can increase yield by producing more young canes; increase fruit size by producing more strong wood; decrease disease by removing dead wood; and increase cane initiation because as pruning increases, cane number increases.


NEW ENGLAND VEGETABLE AND FRUIT CONFERENCE on Dec. 13-15. You can see the program and register on-line at: Note that the conference hotel is now full, but lodging at other local hotels can be found through the Manchester, NH Chamber of Commerce at (603) 666-6600, or

PLUG PRODUCTION AND IPM. Jan. 4, 2006 Manchester, ME; Jan. 5, 2006 Durham, NH; Jan. 6, 2006 Burlington, VT. Info: Cheryl (802) 656-5434 or

PLANT NUTRITION WORKSHOP FOR GREENHOUSE CROPS at the Sturbridge, MA Host Hotel, Jan. 24, 2006 (Snowdate: Jan. 26). Presentations will cover nutrients, disorders, fertilizer programs, testing meters. Bring your meters to be calibrated. Contact: Tina Smith (413) 545-5306 or:

IPM WORKSHOP FOR ORGANIC GROWERS on Feb. 4, 2006 from 12:30-3:30 pm at the Farm and Forest Expo, Manchester, NH. It will focus on efficacy, pesticide safety, application methods, and applicator certification related to pesticides allowed for use on organic farms.