Construction and operation of plastic-film hotbeds for protecting transplants

If you remove the frames and store them indoors for the winter, the service life of the hotbed can be extended to 10 years.

In a standard hotbed covered with polyethylene film, the "double film" effect will help save plants from dying during heavy frosts.

The frame of the double-film hotbed is assembled from wooden bars and slats as usual, but the "foundation" must be reinforced. It is necessary to securely strengthen the pipes that support the frame. This reduces warping, which is important for hotbed operation.

First, the inner film is stretched, followed by the outer one. Special attention should be paid to stretching the inner film sheet at the corners.

The inner film does not need to be welded; in this case, the layers are overlapped with an allowance and stretched tightly. This creates a proper seal.

The most complex part of the hotbed is the opening slope. Fig. 8, b shows a fragment of its general view, components, and design features. In terms of operation, it should be noted that the opening slope, covered with film on both sides, rotates on two bolt-axles. In the open position, it is secured with a wire stay.

Along all touching edges on the opening slope, duralumin strips (1-1.5 mm thick) are nailed on, with a seal made of military overcoat fabric strips glued to them. When closed, if manufactured correctly, the hotbed is reliably insulated from the cold ambient air.

A large hotbed where one can work standing at full height is every gardener's dream. Building it is not cheap and is labor-intensive compared to the structures described above, but it pays off in areas with cold mornings that are dangerous for heat-loving vegetable crops.

The hotbed is calculated and laid out based on the width of the film sheet. It is desirable to have duralumin pipes as building material. Recommended parameters:

You can use pipes of a single diameter.

The general view of the frame and connection points are shown in Fig. 9, a. Particular attention should be paid to the construction of doors and covering the frame with film.

For the end wall where there is no door, prepare a sheet of film with a pocket along the entire perimeter, except for the bottom. It should be 30-40 mm larger than the end wall on each side. A suitable cord is threaded through the pocket, secured at the bottom near the ground, tightened slightly, and the film is placed onto the frame.

The end wall with the door opening is covered in the same way as in the previous case. To the door opening, which is made of wooden bars, the film is attached with a lath (thin slat) and small nails, as shown in Fig. 9, c.

The door sheet has pockets on three sides. Installation sequence:

• Place metal grommets on the pockets every 15 cm.
• Attach the top to the opening with a slat and small nails.
• Nail a soft cord around the perimeter of the door opening (on the sides and bottom) and drive in nails.
• The number of nails equals the number of grommets; they hold the door sheet in the closed position (the film fits tightly against the cord).

The top and sides of the hotbed are covered similarly. At the top, the film sheet is pressed down by a longitudinal slat, which is fastened with screws. At the bottom, the sheet is covered with soil on all sides.

As is known, you must either periodically change the soil in the hotbed or rotate crops. But there is another way — make the hotbed portable and move it to a new location when necessary.

To build a portable hotbed using fishing line, you will need:

• used water pipes with a diameter of 0.5 inches;
• six connecting inserts;
• two 35x35 mm angles for the door;
• wooden bars to connect vertical pipes and angles;
• wooden slats, 3 m wide film, and nylon fishing line.

Before assembling the hotbed, mark the burial depth on pipes 2 and angles 8 with paint. Connect the roof pipes to the longitudinal pipes using inserts 3, attach wooden bars to the outside with screws, and fix a crossbar and film to them. Install the assembled door onto one of the angles.

Stretch the fishing line over the pipes on three sides of the hotbed and on top. In the end-wall vertical pipes, thread it through drilled holes. Bind the walls with the fishing line. After stretching it over the frame, tie it to the inclined pipes. Stretch the film over the prepared frame. Trim it so that some weight (a pipe, board, etc.) can be placed on the ends. Attach the remaining film on the ends to the pipes using screws, nuts, and wooden slats. For the ends of the hotbed, cut the film separately and nail it to the slats using small nails.

It is best to make the hotbed to the full width of the film; it can be made from several such sections. In each section, four rows of transplants can be accommodated comfortably — two beds on each side with a 0.5 m wide aisle between them.

The foundation of a backyard hotbed with automatic irrigation and electric heating consists of a frame made of four straight bars, to which four profiled aluminum bows are attached with special clamps. The film cover of the frame is clamped around the entire perimeter with a rubber cord. The weight of the hotbed, together with the film, is 19 kg for a useful area of 5.5 m2. A foundation of brick, boards, and concrete is built to install the frame.

Automation of heating, irrigation, and ventilation in film hotbeds

A modern hotbed should operate with minimal human intervention, protecting plants from the whims of the weather. Properly configured automation allows for growing transplants from early spring to late autumn without unnecessary labor. Systems for automatic irrigation, soil heating, and ventilation help preserve seedlings even during late spring frosts.

• Frost resistance — down to -5 °C
• Volume of the automatic irrigation tank — 100–200 l
• Number of heating pegs — 20 pcs.
• Total heating power — 0.3 kW
• Freon consumption for ventilation — 100 g

The automatic irrigation system operates autonomously based on simple physical laws. It consists of a storage tank with a dosing device, a distribution tank, a dosing bucket, and feeder tubes with wicks made of water-conducting material inserted into them. Water is supplied directly to the root system of plants evenly and in measured amounts.

To protect against spring cold, electrical soil heating is used. Metal pegs with tips, inside which a nichrome wire resistor is installed, are buried into the soil across the entire area of the hotbed. All heating elements are connected via a socket to a control panel, consisting of a unit with a transformer and a circuit breaker.

The automatic ventilation mechanism is activated by solar heat and does not require a power connection. It is based on a hydraulic cylinder with a piston and rubber sealing rings, filled with Freon-12. The free end of the cylinder rod rests against the end of a wooden post and is fixed with a screw in a blind hole. When heated, the liquid expands and raises the frame through a system of levers and rods, while during cooling, the frame lowers under its own weight.

Frame structures and covers for beds

Arched and collapsible film structures are used to protect early vegetables in beds and ridges. They can be purchased ready-made or easily assembled by hand from wire, slats, and improvised materials. A correct choice of frame parameters guarantees the structure's resistance to wind and rain loads.

When assembling the collapsible-portable wooden cover, it is important to tension the film correctly so that it does not touch the ground. The sheet is attached to bobbins with wooden slats and 30–35 mm long nails with a spacing of 15–30 cm, leaving about 30 cm of film free at the ends. One bobbin is placed at the base of the hotbed, the film is straightened, thrown over the ridge, fixed with a slat on the ridge beam using nails every 50 cm, after which the second edge of the film is attached to the second bobbin in a similar way.

For durability, the combined frame is additionally tied in 2–3 places with twine or aluminum wire, and secured to the ground from below with metal pins or wooden pegs. In southern regions, folding trestles are also popular. They are made of meter-long wooden slats, fastened at the intersection point with a screw or nail, and the lower ends are pointed and buried in the soil to a depth of up to 30 cm.

To ensure that plants under the film receive sufficient soil moisture and do not suffer from weeds, strips of slate 30–40 cm wide are used. They are placed under the edges of the film at an angle to the horizontal, directing the apex of the angle toward the center of the bed. Rainwater flows unimpeded along the slate under the cover to the plant roots, while the strips themselves completely block the growth of weeds in the rows.

For individual protection of single seedlings and transplants, earthen domes or mini-hotbeds are used. Pyramidal or cone-shaped mini-structures are assembled from spokes and rings, covered with film, and secured at the top with wire triangles, quadrangles, or rings. An earthen cover is made using simple improvised tools.

1. Knock out the bottom of an old flower pot or a leaky bucket of a suitable size.
2. Place the form on the bed so that the plant is inside the cone, which widens toward the top.
3. Cover the form with soil on all sides and pack it down firmly.
4. Carefully remove the form with a strictly upward movement, leaving the earthen walls intact.
5. Cover the resulting earthen house from above with a piece of glass.

Transplants or seed are sown in a small hole over which the device is installed, and the edges of the film are covered with soil. Such mini-hotbeds are a fairly effective means of protecting early transplants from frosts.