Winter Greenhouse Secrets
Tips For Protecting Your Plants While Reducing Greenhouse Maintenance Costs
For gardeners who live in colder climates, a greenhouse can be an investment that pays lifetime dividends. There’s nothing more gratifying than watching your seeds and cuttings grow throughout the winter, storing nutrients for a brilliant emergence in the spring.
But winter makes special demands of both the greenhouse and the gardner; it’s a sure test of your greenhouse management skills. The core secret of good greenhouse management is moderation and consistency, which you achieve by establishing a good daily routine and making sound decisions in the fall.
The following guidelines will help you provide a protective haven for tender plants, while keeping your greenhouse maintenance costs low.
GREENHOUSE TEMPERATURE REGULATION
Temperature ? air, soil and water ? plays a major role in plant growth. Most greenhouse gardeners endeavor to maintain a moderate air temperature range because it’s more economical. For most winter greenhouse gardeners, heat is the greatest expense.
Soil temperature is even more critical for most plants, which is why root zone heating has become more and more popular, especially with commercial growers. In general, if air and water temperatures remain moderate, soil temperatures will, too.
But it’s a good idea to buy a good soil thermometer. Move it around to plants in various areas of your greenhouse to ensure that your greenhouse is evenly heated, and that your plants are situated in the area of the greenhouse best suited to their soil temperature needs.
If your greenhouse is too warm, your plants will tend to have smaller foliage and blossoms, pale color, and twisted stems with elongated nodes. Also, you may notice wilting, since warmer temperatures deplete the water available to the roots and cause plants to lose water faster through their leaves and .
Cooler temperatures can actually encourage flowering in some plants, particularly bulb plants. But for many plants, too-cold temperatures can slow or even terminate plant growth, promote wilting, and distort colors.
TIPS FOR USING AUXILIARY GREENHOUSE HEATERS
Choose heaters with thermostats that will trigger the heater to turn on and off at your pre-set temperatures. Plus, you don’t want to have to trek outside in subzero weather in the wee hours because you forgot to turn on the heater. And for some plants, one cold, cold night is all it takes to kill them.
Electric ceramic disc heaters can be very cost-effective, but tend to offer lower Btu outputs, thus don’t provide as much heat. Pricier "greenhouse heaters" offer higher Btu outputs and are usually longer-lasting, since they’re resistant to water and moisture buildup. They provide excellent warmth, but are considerably more costly to run. If you purchase a greenhouse heater, be sure to buy one that has a thermostat or you could be in for some shocking utility bills!
Experiment with lowering the temperature 5°F to reduce heating costs. Over time, some plants adapt to changing temps; others never do — especially the exotics. Lowering the temperature gradually increases the odds of successful adaptation.
Hardening off your plants in the fall will aid the adaptation process. When you first bring overwintering plants into the greenhouse, don’t turn on the heater, as long as the nighttime temperature isn’t dipping into the thirties for any substantial period of time.
Monitor temperature constantly. Place heavy-duty, minimum/maximum thermometers strategically throughout the greenhouse. For accurate measurements, place thermometers halfway up greenhouse walls to protect them from sunlight.
Monitor the thermometers at various times of day. On a cold winter’s day, it can be difficult to keep the whole greenhouse evenly heated. As the winter wears on, thermometers can help you decide whether you need to shift your heaters, or shift your plants to accommodate the shifting sun.
INSULATION: AN INEXPENSIVE WAY TO REDUCE HEATING COSTS
Attaching insulation to your greenhouse walls and ceiling reduces heating costs by 30% or more and helps retain moisture inside the greenhouse. Insulation can be attached with Velcro strips, taped to splice joints, or stapled to wooden framing. Vents should also be insulated, but in such a way that you can still open them on warmer days.
Greenhouse bubble insulation transmits evenly diffused light and works with all types of greenhouse glazing. At a cost of only $100 per 500-square foot roll, it’s an excellent investment that will pay dividends for years to come. A 500-square foot roll only costs around $100.
You may also want to consider a rigid bubble and silver foil combination insulation such as Reflectix, which both insulates and reflects light. Reflectix reduces four kinds of heat loss: radiant, conductive, convective, and infiltration. Reflectix, 5/16" thick, costs around $1.50/linear foot for 2′-wide panels; $3 per linear foot for 4′-wide panels.
WINTER WATERING
Work out a watering schedule, but be prepared to adapt with temperature shifts. During periods when the heaters are constantly running, you may find that your plants dry out more quickly. Don’t wait until your plants are droopy and withered to water. But don’t water them until they wilt. Most plants need far less water in winter.
Water that feels too cold to the touch can cause leaf spots on vulnerable seedlings and even adult plants. Let water reach tepidity in plastic jugs or watering cans. Let the sun warm the garden hose before you use it.
Make sure that you’ve always got a way to water plants, even if your garden hose freezes. Store water in plastic containers inside the greenhouse so that your water will remain at room temperature. Too-cold water will shock your plants. Consider adding an automatic irrigation system to manage your watering schedule and ensure that your plants receive an even supply of water. If you have the budget, consider adding a heater to the greenhouse water line.
MONITOR HUMIDITY
Outdoor humidity is generally low in winter. While lower humidity may make your plants less susceptible to disease, plant growth suffers if the humidity level remains below 50% for long periods of time. Your plants will be losing water faster than it is being replaced. If humidity is consistently, dangerously low, mist the plants and water the floor a couple times each day. You can also purchase a humidifier.
On the other hand, plants are at risk for leaf diseases when humidity exceeds 80%. If humidity is consistently high, ventilate, ventilate, ventilate ? especially on warmer winter days. Fans and skylights will do the trick.
And take care of your hands too, while you’re at it. Low humidity can ravage your skin. Wear gloves while working with soil in the wintertime, and moisturize them with restorative hand lotions that contain natural healing agents such as aloe or rosemary oil.
LIGHTING
Everyone knows that plants must have adequate light to thrive. If your greenhouse gets less than six hours of natural sunlight per day, you may need to provide supplemental lighting.
Incandescent bulbs can provide heat for a limited area, but incandescent light is inefficient light for plants, thus not recommended as a supplemental light source.
Fluorescent grow-lights such as spot or tube lamps running on a timer can help supplement sunlight and grow seedlings.
Combo fluorescents: Use one daylight and one cool white fluorescent tube in a dual fixture to achieve the full spectrum. Cool white fluorescents are even more efficient than grow-lights.
High-pressure sodium and metal halide: One-third more efficient than fluorescents. Available in wattages suitable for greenhouses.
FINAL TIPS FOR REDUCING PLANT STRESS
Don’t wait until the temperature hits freezing to turn on the heat. And don’t wait until the greenhouse is dripping with condensation to ventilate. Plants thrive when they are watered and fertilized regularly, and inspected frequently for growth and pests.
A daily five-minute stroll through the greenhouse will allow you to catch problems before they become a crisis. Good habits and a familiar routine will make winter greenhouse management natural, easy and rewarding.
