Alpine Frame in winter
alpine frame is a structure built to provide plants with extra
protection from winter wet and cold. Alpine
frames are essentially a type of coldframe with provisions
for extra ventilation and shading. Plants
can be grown in pots set into the frame or plunged into sand.
Plants can also be grown directly in the bed in a soil mixture
or sand. Our hinged
top design allows us to easily open the frame on warm days
and close it again in the evening. It is also easy to
tend the plants when the top is open.
Below are photos which show some of the construction details:
We laid ground cloth and built a frame with 2 x 6's - the dimension of this frame is 5 feet wide and 24 feet long. It is important to build the frame top in sections no long than 8 feet (yes, it could be less) for easy opening and closing. Don't use ground cloth if you want to grow plants in your native soil.
We attached the boards to pieces of 4 x 4 at the corners and 2x4's at intervals for stability
The frame is constructed with 2 x 2" lumber with 4 ml greenhouse plastic as a covering.
The wooden frame has a 90 degree angle at the top with 45 degree angles at the sides.
The frames are the sturdiest when each section is no more than 8 ft long with full braces at each end and in the middle at 4ft. The wooden framing is held together with 3 inch wood screws.
Detail of cross-bracing at 4 foot intervals.
4 mil plastic is attached with lath strips and 3/4" screws. The plastic has lasted 4 seasons without needing replacement.
Clear Polycarbonate panels could also be used. They are very durable but more expensive.
Detail of peak of frame before screen end is installed
We created additional ventilation around the base by adding a block of wood with mesh. This is needed only if you will be growing plants such as alpines that require good air circulation.
For a traditional coldframe where maximum warmth and humidity are desired, the covered frame sits directly on the frame.
Hinges are used along the back edge for a frame that can be easily opened and closed.
We put cinderblocks at intervals to support the frame when open.
For good air circulation, we left the ends open and covered them with wire mesh to keep rodents (and cats) out. The ends could instead be covered with plastic to hold in heat, creating a more traditional coldframe.
This design sheds snow well in our relatively mild winter Pacific Northwest climate.