An Orchid Hothouse

The current layout of the Rittmans' backyard contains just enough unused space to allow for the addition of a hothouse, which will be built directly against the back wall of the couple's garage. Since the Rittmans are also concerned about the structure's aesthetics, McMurray will enhance its exterior with climbing vines and perennials. (In addition to integrating the hothouse with the garden, these plantings will also add color and form to the somewhat dull and overgrown yard).

Step One: Building the Frame

Master carpenter Bill Bedard is using pine for the framing, which is inexpensive and readily available in all regions of the country. Bedard explains that if the pine is treated with water sealer, it will work just as well as Douglas fir or redwood. He also likes the lightweight aspect of pine, which will provide sufficient support for the plastic sheeting that will form the hothouse walls. Next, the crew constructs the top plate of the structure using pressure-treated 2x4s. The boards are placed horizontally between the posts, screwed to tops of posts with deck screws so that they extend span the distance from one post to the next. More 2x4s are used to form the bottom plates (figure C). The crew lays the ends of the boards on the edges of the pier blocks so they fit tightly against the bottom of the posts, then toe screws them to the bottom of the posts.

Durable plastic sheeting is used for the walls and roof. (McMurray says the sheeting must be at least 6 ml thick to withstand the elements, and explains that colder climates will require heavier material or a double thickness). First, the plastic is stretched across the structure, then small pieces of scrap wood are placed over the points where nails are driven; these prevent the plastic from ripping.

Along the bottom of the long outer side, Bedard and McMurray nail on more 2x3s over the sheeting to form a frame for a panel of corrugated plastic sheeting on the lower third of the wall. Next, they attach lengths of thin corrugated foam strips (sold with the fiberglass) to the perimeter of the roof and the vertical edges of the lower wall panels. The strips will fit into the peaks and valleys of the corrugated sheeting and form a tight seal.

Next, Bedard lays the corrugated plastic in place, and attaches the plastic with screws driven in through rubber washers that make watertight joints. He uses more 2x3s for the door, which features two diagonal lengths of wood fitted across the front (one near the top, one near the bottom), with an angled top edge that fits snugly beneath the sloped roof line. Finally, he fits the door in the designated space in the end wall and attaches it to the outside of framing.

Featured Orchid Varieties

• Phalaenopsis
• Oncidium
• Cattleya

Other Featured Plants

• Sweet Olive (Osmanthus fragrans), Zones 9-10 (not appropriate for cold climates)
• Lavender (Lavandula angustifolia), Zones 5-8 (cold-climate alternative to sweet olive)

Before the shelves are installed, McMurray uses black plastic sheeting to line the floor of the hothouse. Then he lays down a 1-1/2-inch layer of pebbles over the plastic. Here, "California Gold" pebble is used; other types and colors may be preferable based on personal taste, availability, etc.

McMurray then lays down a line of pavers in the gravel to form a pathway that extends from the door to the opposite end of the hothouse.

Bedard builds the potting shelves along both long sides of the structure, using more pine 2x3s. First, he constructs the surface framework (the corners are joined with deck screws), which he nails along the existing wall, and secures into the studs of the new of the opposite side. Pressure-treated 4x4 posts form the supports .

To form the surface of the shelves, Bedard lays 1x2s across the top of the framework, using a 1x2 turned on its side to serve as a spacer. Then, he nails each length securely in place.

McMurray says that while climate control in a greenhouse or hothouse can involve a complex system of devices and mechanical fixtures, it can also be created with a few cost-effective items from building supply stores. Here, he uses an evaporative cooling fan (mounted on the framing of the end wall opposite the door), a kerosene heater and a forced air heater; bamboo-slat sheeting is laid over the roof so that it covers the long outer wall and provides shade when it's needed.

To ensure plenty of moisture in the hothouse, McMurray also installs a simple misting system, which is comprised of emitters attached to thin hoses that he secures to the rafters. For those concerned with excess moisture causing diseased plants, McMurray advises installing the emitters along the walls instead.

Finally, McMurray builds waterproof covers for the fan and heaters to protect them from the misters' spray.

Orchid expert Dr. Robert Hull explains that plenty of light is essential for healthy orchid blooms. And although water is also an important need, Hull, warns against over-watering, a common mistake made with orchids. (Hull advises checking the soil's moisture level an inch below the surface; if the soil is still damp at this depth, it doesn't need watering yet.) To further encourage robust blooms, apply an orchid fertilizer diluted to half-strength about once a month, and make sure air is able to circulate freely around the plants.