High Energy Costs BluesOSU Department of Horticulture & Crop Science The last time I wrote about this issue I mentioned that many growers were worried about the high cost of gas for heating their greenhouses. Unfortunately, almost a year later the situation has not improved. While the poinsettia sales season will start reaching its peak, growers are thinking how to deal with this issue for the Spring crops. Following are some considerations to help alleviate a problem that has no easy answer. 1) No silver bullet. Other than a substantial drop in the price of gas and fuel, there is no single factor that will help growers save money on energy. There are however a series of small steps than can have a cumulative effect and translate into substantial savings. 2) Saving energy is a continuous, slow process. Today’s savings will be the result of grower’s past planning: How energy efficient is the last boiler they bought? How tight are the last structures they have built or renovated? How good was the last gas price they locked in? If a grower has never paid attention to saving energy and wants to start now, he/she’ll be laying the groundwork for future savings that will take a while to materialize. Everybody should keep in mind that high energy costs are here to stay. 3) Medium/long term actions. There are always actions that can be taken today that will help growers reduce energy expenses. If growers have the capital, they should start planning today so they can install what will help them reduce their energy costs: a) radiant floor heating; b) insulation curtains (thermal blankets); and c) new burner technologies. 4) Short term actions. To be done now and a relative low cost: a) Greenhouse weatherization. Always remember that a typical greenhouse structure retains heat as efficiently as a colander holds water. Check your greenhouses for leaks. I am amazed at the number of greenhouses (specially old ones) that have doors that do not latch properly leaving gaps through which large volumes of heat can escape. This loss grows proportionately to the differential of temperature inside and outside. Metals conduct heat so all metal parts having contact between the greenhouse interior and exterior should be insulated. For example, metal gutters of gutter-connected greenhouses have one surface on the (warm) interior and the other surface on the (cold) exterior. Some growers insulate the interior surface of gutters with foam to reduce heat loss. One word of caution before improving insulation: growers located in climates with heavy snow falls benefit from their heat inefficiency because snow melts fast on their greenhouse roofs. If snow does not melt and accumulates on the roof, the greenhouse can collapse due to snow weight. There are good sources of information on how to weatherize greenhouses, for example the website of the National Greenhouse Manufacturers Association (www.NGMA.com). b) Do not place crops on the floor. This advise is for all soils but specially for those that are unheated. If putting the crops on benches is not feasible (bedding plants growers usually have many flats directly on the floor), at the very least, flats should be raised 3 or 4 inches from the soil surface. Unheated soils are usually colder that the greenhouse air. It takes more energy to warm up the roots of plants that are sitting on the soil than those that are separated from it. In addition, warmer roots are less prone to diseases. c) Lowering greenhouse temperature. It is very tempting for growers to change their thermostats during periods of high fuel costs. However, they should remember that temperature affects the development of plants: at lower temperatures, it takes longer to reach the point when the crop is ready to be sold. If growers are not careful, they may simply lower the heat but extend the period of time needed, negating all savings. While lowering temperature reduces development rates of all crops, such reduction is crop specific. In other words, some crops are cold-tolerant, meaning that they grow relatively quickly in a cool greenhouse. Other crops are cold-sensitive, meaning that they grow very slowly when greenhouse temperatures are reduced below their optimum. Growers should be very careful when deciding to reduce their greenhouse temperatures. Knowing the response of the crops to low temperature is important. One way of doing it is through compartmentalization. Creating compartments in a large greenhouse or using different separate structures to house crops with different temperature requirements represents a way of saving fuel with crops that tolerate low temperatures and even increasing quality for crops that prefer it warmer. Snapdragon, osteospermum, cyclamen, dianthus, alyssum, petunia, marigold, etc. can be grown in a separate house or section at a lower temperature. On the other hand, begonia, vinca, celosia, New Guinea impatients, pepper, etc. should be grown in a separate compartment at higher temperatures. Avoid reducing temperature at critical stages of plant development such as germination, floral initiation, and floral development. d) Greenhouse weatherization. At least for a few days, before selling the crop, growers can gain some energy savings while hardening their crops. Usually, towards the end of the crop cycle temperature reductions are positive since they allow keeping the crop in the greenhouse for a longer time while producing its hardening before it is sent out. For example, marigolds can be grown at 60 F but can be hardened at 50 F; pansies can be grown at 55 F and hardened at 45 F. As a rule of thumb, hardening can be achieved at temperatures 10 F below growing normal temperatures for many crops. This hardening process can be done only if compartmentalization is possible. Steps to Success - Log on to the internet and go to the National Greenhouse Manufacturers Association (www.NGMA.com). Look for their information on how to weatherize greenhouses. Inspect your own greenhouses, look for possible heat leaks and take care of them. If in doubt, contact Dr. Peter Ling at OSU/ORDC in Wooster (ling.23@osu.edu). - Contact your suppliers and develop a plan to incorporate in your production facilities some radiant floor heating, insulation curtains (thermal blankets), and new burner technologies. - Develop a compartmentalization plan. Study the requirement of all your crops and separate them in 3 temperature groups: high, low, and intermediate. Plan to grow these crops separate giving them the appropriate temperature.
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