THE ""100-YEAR"" HOTBED

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Issue # 178 - February/March 2000

by Tony Gross

Here are plans for an industrial-strength hotbed that you can put to use eight months a year or more in most climate zones. It features nearly 18 square feet of protected planting area and a foundation built of lightweight, concrete partition blocks that's worthy of a house

This hotbed is rugged enough to last for many years, while withstanding the worst weather that nature can muster. To good to be true? Hardly. The best part is that it's easy to build, and you can do it in a weekend.

A hotbed allows you to jump-start your garden several weeks early in the spring. In passive mode, it collects and concentrates the sun's heat in a small, confined area - perfect for starting or hardening off seedlings and young plants. It will also protect late plantings of hardy varieties well into the fall. In active mode, when artificially heated the old-time way by a layer of fresh, "hot" livestock manure under the planting medium or else with modern electric heating cables, it can add weeks more onto both ends of the growing season.

1. LAYOUT

Locate your hotbed on shade-free, flat ground. Scalp grass or cut out sod in a rough 4' x 8' rectangle-long dimension running east-west to face south and catch the most sun. Along the inner perimeter of your rectangle, layout an 8"-wide, rectangular trench to be dug to below frost level. This will hold the concrete-pad footer and concrete-block foundation walls of your hotbed. Next, sink stakes at each outside corner of the 4' x 8' plot. Run a line around the outside of the stakes to define outer dimensions of the foundation. The outer corners of your rectangular plot should be 48" apart in the narrow dimension and 96" apart in the long dimension. Use a steel square to make 90° corners. To test squareness, each diagonal should measure precisely 107 1/3" between outside corners of opposing corner stakes.

To lay out the inner walls of the foundation, sink 8 more stakes along each outer-wall string line, 8" in from each side of all 4 corner stakes (measure between outside corners of stakes. Fasten 4 strings between the 8 inner stakes so they run parallel to,and 8" in from, the outer string line. The 8"-wide ribbon between the lines is where your concrete block foundation walls will go. (A fourth stake may be added at each of the four corners, where the inner strings intersect, to mark the inner corners of the foundation walls; see "Layout Lines" illustration.)

Press strings to soil level and using a nontoxic spray paint mark soil under the lines-tracing one rectangle inside another-to define inner and outer boundaries of the 8'-wide trench