Archive for November, 2005

A lath house is usually an outdoor open structure with slat top and sides for the primary purpose of providing shade. In warmer sections of the country, such as Florida, Texas, and California, the lath house is an essential part of the greenhouse-growing operation. In such regions, for 9 months of the year- sometimes more-lath houses permit gardeners to grow many of the tender plants that northerners can grow only in the greenhouse.

In the North the lath house is equally valuable. It provides a summer work area, as a potting shed or sales room, and it is a fine place for growing specimen potted plants which may take too much greenhouse room.

There is no special design for a northern lath house; it is built to fit the space and the gardener’s requirements. A small one will take care of an overflow of large begonias and ferns and provide a shady spot for a few specimen plants of caladium and fuchsia. Situated between the greenhouse and the garage, our 10- by 12-foot lath house has an east opening. We ripped 2 by 4’s to make the open-squared roof of the structure. The walls are formed by the greenhouse on the south; our house on the west, and the garage on the north. Morning glory vines clambering over the front prevent strong sun rays from burning the plants.

Inside the lath house is a long table for potted gloxinias and caladiums. By midsummer the gloxinias have finished flowering and can be dried off for fall sales. Some of the caladiums will also be sold, others stored for landscaping our patio. In any case, although there are many ways and means you can use to build your lath house-and many different styles- you will find that the basic structure of the house begins with the corners and four roof stringers of 2 by 6’s. You can rip 2 by 4’s as we did for the top, sides, and ends. Also, you can use regular lath, or purchase specially designed shading material.

In the South and West, gardeners often extend the seasonal use of the lath house by placing plastic over it during the colder months of the year. Redwood is a favored lath house lumber because it blends with plantings and it is one of the most durable of all woods. Redwood needs no finish and little upkeep. The same companies that offer greenhouse construction information can help you with your lath house.

A hotbed, obvious as it may sound, is basically a cold frame with heat. While cold frames receive all of their heat directly from the sun, hotbeds are heated with electric soil cables, stable manure or steam, or hot water heated with flues. The hotbed can be used earlier in the spring and later in fall and early winter than the cold frame.

Hotbeds are constructed just the same as cold frames, with a slope to the south to admit heat from the sun and to allow water or snow to run off. Plants growing in these frames are protected on cold spring nights with the same kind of mats suggested for cold frames. Hotbeds are usually built to be permanent structures, with the frame of wood, concrete, or brick extending into the ground below the frost line. As with the cold frame, you can build it yourself, purchase a kit of materials for building it, buy a ready-built one, or have someone construct the entire thing for you.

A soil-heating cable furnishes the simplest kind of heat for the hotbed and these cables come in a variety of sizes and prices. The type used for hotbeds is insulated and enclosed in lead or plastic sheathing. The cables are made in several lengths but the most useful sizes are 40, 60, or 80 feet, all adapted for use with an ordinary electric service of 110 volts.

A 60-foot cable will heat a 6- by 6-foot hotbed. You should reckon your cable to suit your space. Each 60-foot cable carries an electrical load of approximately 400 watts. In our area the cost of operating such a cable on a continuous 24-hour basis is about 1 cent per hour. You should have a thermostat to regulate air temperature and another to regulate soil temperature. However, you will find that during many hours of the day the sun will heat the hotbed enough so the thermostat shuts off the current. As spring nears, the outdoor temperature rises and the artificial heat will be on for shorter periods of time.

You can conserve heat by making certain that all construction is tight. Bank the sides of the hotbed with earth and check the sash-it should fit tightly. If it doesn’t, weather-strip the top of the frame. Make sure that all glazing is well puttied and that it laps J4 inch at joinings. Keep the glass clean to admit maximum light. In my area it is not practical to use a hotbed before March first. As the spring temperature increases, start ventilating the hotbed by raising the sash a crack. This applies equally to cold frames. From midday until mid-afternoon on warm spring days, you will have to ventilate more. Be sure to close the frame before the temperature falls at night.

Installing the Heating Cable

You will need an electrical outlet close to the frame, so you can connect the soil-heating cable. Place an inch of sand on the floor of the frame. Loop the cable back and forth over the sand. Cover with 2 inches of sand and a layer of hardware cloth (coarse wire mesh). If you grow plants in flats, place them directly over the hardware cloth. If you plant seeds or cuttings in soil-without flats-add about 4 or 5 inches of good soil.

Owners of home greenhouses invariably have one problem in common. They do not build them large enough. This is an especially knotty situation for those of us who have profit in mind. If you are in this boat, you will welcome ideas on obtaining more growing space with the use of “auxiliary growing facilities,” such as cold frames, hotbeds, and lath houses.

A cold frame is an outdoor growing “area” built without a bottom but with a solid-sided frame of wood, cement or brick, and a removable hinged top, glazed with glass, Fiberglas, or plastic. Cold frames are invaluable. For instance, they take some of the spring bulge from a greenhouse. By using them for growing greenhouse-started annuals and perennials, you make under-glass room for a new crop of salable plants. Then there are plants such as delphiniums, pansies, and Oriental poppies, to be planted in the frame in late summer and kept there over winter. The cold frame makes an excellent “cold-42 conditioning” rooting area for the spring-flowering bulbs you wish to force.

You can purchase material and build your own cold frame, buy ready-fitted supplies from a greenhouse dealer and assemble it, or you can buy a ready-made cold frame of wood or aluminum with plastic “lights.”

The frame should face south. If you are going to have but one frame you might want to attach it to your south greenhouse wall. If you plan on a number of frames, build them in rows either free-standing in the garden or attached to the greenhouse, garage, or other building. In cold-winter areas the frames should be provided with a cover of matting, either the roll-up kind or straw mats. Wooden slats, cheesecloth, and shading paint compounds help protect plants in the frame from summer sun.

Standard-sized sash for use on the frame come 3 by 6 feet. If you purchase this, you will have to govern the width and length of your frame accordingly. However, you can use any kind of window frame, and with so many home owners converting wooden window frames to aluminum, you may be able to get wooden storm sash for little or no cost from almost any window or wrecking company, or through a want ad in your local paper. It may be easiest for you to obtain the sash and then construct the frame around it.

Here’s how we built our cold frame. For the back we used the cement wall of our garage. The frame is 18 inches high in the back, sloping to 8 inches in front, to allow water to run off. Lumber, 2 by 12 inches, 14 feet, forms the front. The sides are 28 inches long. The lights (three storm sash) are hinged on a 2 by 4 wooden strip which is nailed to the garage wall. If you live in a cold climate and plan on using the cold frame for year-round growing, build it on a concrete or brick founda-

13, 14, 15, 16. For a free-standing cold frame, assemble a heavy wooden frame higher at one end, attach a snug-fitting hinged top, cover with reinforced plastic, and this valuable auxiliary growing area is ready to provide protection for seedlings, cuttings, etc. The sides should be banked with soil to eliminate drafts, as described. (Courtesy Workbench)

17. There are the many kinds of ready-made cold frames on the market, such as this aluminum, plastic-covered model. (Photograph by Merchant & Evans)

tion which extends below the frost line. In my area the building code specifies that the frost line is 42 inches deep. On sunny days, even in midwinter, you’ll have to be careful about ventilation. Heat can build up rapidly in the confinement of a cold frame and “cook” the plants. A notched stick will make it easy to raise the sash cover as needed.

Mr. and Mrs. F. O. Reh of Belleville, Illinois, have pioneered in Fiberglas greenhouses, and their experience is valuable for every grower. In their first plastic greenhouse, the Rehs used 40- by 140-inch sheets of corrugated plastic for the roof. A clear mastic was used to seal the plastic sheets together. (The sheets can also be “cemented” together with a weatherproof adhesive tape.) An overlap of one corrugation was used. The sheets were fastened to the various supports with galvanized screws, set with lead washers. In this greenhouse, there are no provisions for vents in the roof, but four screened ventilators at ground level allow air intake. Top ventilation is provided by a thermostatically controlled low-speed fan. This fan makes an air change in the house every 7 minutes without creating any drafts.

The fibers of glass in the plastic and its crinkled surface diffuse the light without casting shadows. In this greenhouse every inch of space is available for growing plants. Eighty-five per cent of the visible light is admitted but a large percentage of the infrared (burning rays) are screened out. The sunlight in this plastic greenhouse is like the light in a glasshouse on a slightly cloudy day.

Flat plastic sheets make up the side walls of the Reh greenhouse. These sheets, measuring 36 by 72 inches, are fitted with edges butted; the seams are sealed with the sticky mastic and covered with cypress molding. The greenhouse does not have a solid foundation wall; the plastic material extends to ground level giving full-length light for growing plants.

Belleville is located in the southwestern part of Illinois. The seasons are variable. Although the temperatures never dip as low as in Minnesota, it is necessary to make some provision there for heating a greenhouse. The Reh heater is a propeller fan type with steam entering a finned coil through which the fan draws air. The adjustable heater blade “pushes” the warm air in any desired direction. This circulating heater, controlled by a thermostat and an aqua stat, is suspended from the roof. It collects and circulates the cooling humid air from under the roof before moisture condenses, and fans the air back to the plants in the form of a warm, humid breeze. Since the heating unit is up near the roof, it also eliminates drip, which in conventionally heated glasshouses is caused by the condensation of moist air when it strikes and collects on the chilled glass roof. More than annoying, a regular drip of water falling on plants is a disease hazard.

Mechanical controls of temperature and humidity in this plastic setup are largely automatic, and the effects are indeed different. On the warm summer day when I visited the Rehs, the outside temperature was in the high nineties. Inside the plastic house the temperature was 85 degrees, and the air as balmy as on a spring day.

Prefab Plastic Houses

One typical, small, prefabricated, plastic greenhouse comes packed in a do-it-yourself kit. The 6- by 8- by 7-foot model sells for under $80.00. Extra 4-foot sections are available so you can extend the house as much as you wish. The manufacturer claims it will stand up under 50-degree-below-zero weather. He recommends for it a $15.00 electric heater.

A manufacturer of prefab greenhouses puts out a delightful 10- by 12-foot Fiberglas house with an aluminum frame. This house eliminates hail damage, glass replacement, and periodic painting. Still another manufacturer of prefab greenhouses includes with his greenhouses a Fiberglas roof.

Crops for the Transparent Plastic House

Many growers use the plastic greenhouse just as they would the cold greenhouse. They grow spring bedding plants and vegetables in it and, during summer, use it to store large specimen plants. Other growers use the plastic greenhouses the year round for growing potted African violets, wax begonias, geraniums, and so forth. The care of plants in a plastic greenhouse, if it is well ventilated, approximates that of under-glass plants. If there is only side-ventilation, you should install a fan to circulate fresh warm air in winter and to bring in cooler summer air.

If your crops need shading, do not use a material with a linseed oil base. This soaks into the plastic and can never be removed.

Other Uses for Plastic

Both transparent and corrugated plastic can also be used for glazing a cold frame or lath house. In these structures you can harden off annual and perennial seedlings, getting them ready for spring sales. Or you can start any of the plants recommended for growing in a glass-glazed cold frame. (See Chapters 5 and 13.) And there are many uses for plastic inside the glass house. I use thin sheets of transparent plastic to cover flats of seedlings or cuttings. It helps to maintain constant moisture and cuts down the time spent on watering the plantings. I like plastic bags for storing tubers and bulbs. Also, I fasten sheets of transparent plastic inside the glass house to provide insulation against cold and so cut down on heating costs.

You can use plastic on any type of greenhouse structure- lean-to, span, partial span, or free-standing.
If you are using plastic as temporary glazing (until you can afford glass), you will want to construct the greenhouse frame so it will eventually hold glass. However, if the whole thing is to be but a temporary arrangement for a season or two, you can cut construction costs by building with low-priced, smaller-dimension lumber.

The sheet plastic comes in 100-foot rolls in widths of 10 to 20 feet. It takes two people to put it on. One tacks the plastic at one gable next to the top of the greenhouse. The other holds the roll of plastic, releasing enough to cover three or four sash bars while pulling tightly on the roll. The first person then tacks on lath down to within 8 inches of the bottom of the strip of plastic. The second length is placed under this 8-inch lap, so there is a lap of about 6 inches, and the second length is then tacked in the same way. If the lap is about 6 inches and the plastic is pulled tight, there is no need to seal the laps since they will stay together even in strong winds. If you want a double-layer covering-and it’s advisable-the inside layer can be attached with paper disks and tacks. Be sure to allow an inch or so between the layers for “dead air” insulation.

In my greenhouse, ventilation is obtained through doors and louvers in each end. Other greenhouses are ventilated by doors and side drop vents.

12. Lightly-framed plastic greenhouses (made of one of the inexpensive
films) offer a good yet low-cost solution for the grower who needs a
temporary extra growing area or an easy-to-erect plant shelter in an
emergency. (Photograph by Gottscho-Schleisner)

An experimental house 18 by 24 feet, built by the University of Kentucky, cost $24.00 for the outside layer of .0015-inch plastic. It was estimated that the framework would cost from $150.00 to $250.00. A blueprint of this plastic greenhouse is available for 10 cents through the Agricultural Engineering Department at the University of Kentucky in Lexington.

Plastic Greenhouses

Plastic, as a substitute for glass in greenhouse glazing, is here to stay, but it is still in the experimental stage. It probably always will be, as long as new materials and different uses continue to appear, so you will have to keep yourself abreast of new developments. Two types of plastic generally are used: smooth transparent sheets of polyethylene and vinyl film, and corrugated and special types of plastic such as Fiberglas, Al-synite, Mylar, Filon, and Corrolux. Commercial builders are finding the smooth film plastic increasingly useful, especially when they want economical, rapid construction for additional plantings or a quick seasonal crop and aren’t too concerned with the lasting qualities of the glazing. (See Photo 12.) The more expensive corrugated types have great endurance. Tests indicate they may last 25 years without deteriorating.

If at first you can’t afford to build a regulation glass greenhouse, try one of the transparent plastic types. The investment is low, and growing plants in any kind of a greenhouse is a good way to gain experience.

Those who have had experience with plastic glazing are generally agreed on the following resume: “Plastic glass has exceptionally high strength, with low weight, is shatterproof, translucent to light, resists weathering, is not attacked by rodents or termites, will not rot, and transmits approximately only 40 per cent as much heat as glass.” The last point means that plastic greenhouses are usually cooler in summer and warmer in winter.

Advantages and Disadvantages

Polyethylene, Vinyl, Renolon, or other types of transparent plastic cost about 4 to 16 cents per square foot, depending on thickness. Such plastic is easily attached to the greenhouse framework and all puttying is avoided. It’s possible to construct a small 6- by 8-foot free-standing greenhouse for $60.00 or less-providing, of course, that you do all the work. The modern, improved plastics successfully resist strong winds and heavy snow, and transmit up to 98 per cent of the sun’s visible light energy-as much as passes through good glass. Some plastics also transmit up to 80 per cent of the ultraviolet rays, which is greater than through glass.

Two layers of plastic-one inside, one outside of the glazing frame-with an inch of space between them, provide excellent insulation, thus decreasing the cost of heating. Transparent plastic usually deteriorates rapidly and must be replaced every year or two. Certain new plastics being marketed are said to last up to 5 years.

The corrugated types are expensive. However, these have a long life, never need shading, and are not damaged by hail, snow, or such pests as termites. They admit up to 85 per cent of the sun’s visible rays. They are not ideal for the real sun-loving crops-annuals, geraniums, cacti, etc.-but fine for orchids, African violets, anthuriums, rex begonias, ferns, and similar plants requiring medium- to low-light intensities.
Ventilation for plastic greenhouses is somewhat of a problem. Most of them are ventilated through hinged sash on the walls rather than the roof, but a better system is to have sliding panels in the gable ends to allow more thorough ventilation. Corrugated plastic, slightly rust-tinted in appearance when new, darkens as it ages, gradually shutting out some of the light.