Grow Heat Loving Plants

Winter 2007-2008
Compost Pile
A large compost pile is made with a 25-foot length of snow fence. Green (nitrogenous) and brown (carbonaceous) layers of organic materials are alternated.

By Adam Tomash and June Zellers
© 2007
Photos by the authors

Eggplant, peppers, tomatoes and cucurbits are among our favorite crops. All require warm soil and a fairly long growing season, which means they need a protected, heated space in the cool Maine spring. We are gardeners growing for our own consumption and can’t justify the expense or complexity of a heated greenhouse – but we have found a way to produce these crops reliably year after year without a permanent greenhouse.  With little added effort or expense, we start with a chore we are already accustomed to doing – building a compost pile – and then use the heat from this pile to “fuel” a small hot house.

The key to producing vigorous plants and reliable crops of any variety is to treat the plants like the living beings they are – tender babies who need certain conditions to thrive. Heat-loving plants really need seven things from the end of April until the weather cooperates to allow transplanting into the garden: warmth; high humidity; adequate light, moisture and nutrients; room for their roots; and lack of stress.  When June is rainy and cold, these heat-loving plants need a way to continue to thrive until the weather permits transplanting into the garden. Transplanting into the garden in June when the soil is cold and the weather wet is a serious mistake. At best, these conditions arrest plant development and gain no time for the gardener.  At worst, they lead to disease and a poor crop.

Durawall sections are used to form arches over the compost pile.

Our solution is four-fold. One, we provide warmth, high humidity, plenty of carbon dioxide and full sun during this time by erecting a temporary plastic structure on top of a biologically active compost pile. Two, we use a triple transplant method, moving plants to increasingly larger containers as they mature. The final containers are recycled, half-gallon cardboard milk and juice cartons with tops and bottoms removed, which provide enough room for strong, unchecked growth until we transplant into the garden. Three, we use a potting mix with adequate nutrition and supplement with compost tea.  Four, when we transplant into the garden, we minimize root disruption by cutting the cardboard containers.

The Temporary Hot House

We use snow fence in 25-foot lengths to build large circular piles of garden waste and leaves in the fall.  These piles often stay well above freezing all winter but don’t actually have time to decompose much. This is our “carbon” source pile.

In the spring, we start the actual ”hot house” compost pile, using overwintered refuse from the carbon source pile and adding vegetative material that is high in nitrogen (N) to help promote biological activity in the piles.  We use the same 25-foot snow fence circles to build these “hot house” compost piles, and the snow fence then becomes part of the hot house.

Durawall has been inserted into holes drilled in the tops of 2x4s. The plywood will sit on top of the compost pile, and seedlings will be placed on the plywood.

Grass clippings, dandelions and/or alfalfa meal supply the N needed to generate heat and effect decomposition. Any high-N material could be used, including animal urines, beddings and manures. We use primarily old, partially decomposed leaves as a carbon source and alfalfa meal as an N source, as they are easily available to us.

We build the pile over two to three days by alternating layers 6 to 8 inches deep of partially rotted leaves or other carbonaceous material with layers 1 to 4 inches deep of  greener, nitrogenous material.  For example, baled, quality, green hay layers would be 4 inches deep; dandelions or grass clippings, 2 inches; and dry alfalfa meal, 1/2  inch or so. We used about five 50-pound bags of alfalfa meal and clippings from one early mowing of our lawn (less than 1/2 acre) in 2007 to build the whole pile.  (Soybean meal can be less expensive, but it is not available to us locally, and is more likely to be genetically engineered.)

Each layer is moistened as it’s added, and layers are added until they reach the top of the snow fence.   After the pile settles for a day or two, we fill it to the top again and continue adding layers until the weather starts to get warm.  The surface of the pile will reach 80 to 90 degrees, and the core temperature may be much higher.

We build our temporary hot house on top of this active compost pile. First we wrap the circumference of the pile in plastic to contain heat. A rope holds the plastic in place and serves as a place to clip spring clamps.  Then we build a temporary framework that will hold a second, outer plastic covering. This temporary framework consists of simple 2 x 4s, metal hoop supports known as Dura-Wall, and four metal posts to anchor the structure to the ground.  The structure goes together quickly in the spring and disassembles just as quickly in early summer.

The completed compost-hothouse. Compost from the previous year’s hot house sits to the right of this year’s hot house and is ready to be applied to the garden.

We fasten two wooden legs to a 2×4 so that the 2×4 will be held at the height of the snow fence when the legs are placed on the ground. The 2×4 is the same length as the diameter of the snow fence enclosure (about 8 feet).  Two of these 8-foot 2x4s with legs are made, and they are placed parallel to one another just outside two “sides” of the snow fence enclosure.  The 4-inch side of these 2x4s should touch the snow fence tangentially. (See photos.)

The 2x4s are wired to the snow fence at their midpoint. Small steel fence post are driven next to each of the four legs, and wire attaches each leg to the steel post so that the 2×4 is reasonably level to the ground. Using a level and tape measure ensures that things are level, parallel and plumb.

When we first built this structure, we drilled the 2x4s to accept the Dura-Wall, which arches from one 2×4 to the other. The 2x4s should be 8 feet apart, and the Dura-Wall is 10 feet long, creating a decent headspace under the hoops. We use the Dura-Wall to mark where holes should be drilled. Each piece of Dura-Wall gets two holes, and five sections of Dura-Wall are used.

We drill into the top of the 2×4 at an angle and make a drill stop with tape on the drill bit to prevent drilling all the way through the wood. (If the Durawall goes through the wood the ends will rip the plastic.) We angle the drill so that the Dura-Wall will make an arch when inserted into the holes from the top.

The “greenhouse” is ventilated on May 27, 2007, by holding the plastic open with clamps. Plywood provides a surface to hold milk carton transplants and plug flat transplants. Green shade cloth protects young, tender transplants from full sun.

Once the arch is formed and all is securely wired together, we stretch a 25′ x 25′ piece of  plastic over the structure, starting from either side, stretching and centering the plastic over the roof, and moving it along the Dura-Wall, not against the grain. If some Dura-Wall moves out of place, we just reposition it.

Excess plastic on the sides is rolled onto a 2×6, rolling in toward the compost pile so that water won’t be trapped in the plastic. The wrapped plastic is tucked neatly against the sides of the compost pile. One large bucket or two small buckets of rocks on the 2×6 hold it down. Wind can be a serious adversary to this project.

Similarly, the rear plastic is tucked against the back, and buckets secure it. This side may need to be opened in very hot weather. The front side is kept in place primarily with large, heavy-duty spring clamps fastened to the rope encircling the snow fence. It is opened every morning and closed on cool nights as long as necessary.  Shade cloth overlays must be used when plants are first moved into this warm, sunny environment if the plants have not been exposed to full sun.

The temperature in the hot house is remarkably stable and requires no fossil fuels or heaters that may break down just when needed most. For instance, this year we had a cold snap in early June. The outside temperature at 6 a.m. on June 7 was 40 degrees. The temperature in the hot house was 75 degrees. The next morning, the outside temperature at 7:30 a.m. was 55 degrees; it was 80 degrees in the hot house. If we get exceptionally hot weather in early June, we also cover the structure with shade cloth and open one or more ends to maintain temperatures in the mid-90s.

Reused milk cartons not only grow great transplants but also serve as labels that stay with the plants.
Milk cartons are slit almost to the bottom before transplants are set in the garden.

Milk and Juice Cartons as Plant Containers

We chose half-gallon cardboard milk and juice cartons, with their tops and bottoms cut off, for several reasons.  They are large enough for roots to really develop, allowing plants to remain in containers until late June or even early July if the weather requires. They are readily available, and reusing conserves materials. These containers are also easy to cut, minimizing transplant shock. They can be labeled with a marker, and the label stays with the plant during transplanting. Finally, a band of uncut carton protects the plant from cutworms, and folded down sides reflect sun onto the plants. (See photos.)

We fill these cartons with our own potting mix:  4 parts peat moss, 4 parts completely finished worm compost, 1 part vermiculite and 1 part perlite, by volume, mixed thoroughly and screened through 1/4-inch hardware cloth.  Instructions for building indoor worm bins were in the June-August 2003 MOF&G and are at (under “Publications” and then “Articles for Reprinting”).

Our potting mix is deficient in N, so, for best results, we water plants with compost tea.  We make compost tea with 2 gallons of compost, 1 cup of seaweed granules, 1/8 cup of Growplex SP Humic Acid (Menaffee humate extract from Fedco), 1/8 cup of powdered seaweed, 1/2 cup of fish emulsion and enough water to make 25 gallons.  The tea is aerated with an aquarium air pump until all of it is used. We dilute the tea with an equal amount of water and apply it to plants once a week

For eggplants, peppers and tomatoes, we use a three-stage transplanting schedule.  Seedlings are started in Kordpac containers set on a heat pad, in a heated basement, under grow lights.  We start peppers and eggplants during the second or third week of March and tomatoes during the second week of April.

Once the true leaves appear, the seedlings are transplanted into 38-cell plug flats and are moved upstairs to the southern exposure window in our living room. By the end of April, however, the sun is high enough in the sky that the living room gets less light than these plants like; it’s time to build the hot house outside. The appearance of dandelions also indicate that it’s time to build.

At the end of April or first week in May, after the hot house is built, we transplant the seedlings into half-gallon cartons, labeling the cartons as we transplant. The half-gallon cartons are arranged in wooden trays that we build to hold up to 18 cartons, and the trays sit on plywood in the hot house. For instance, a 22″ x 12″ x 2-1/2″ flat holds 18 containers. Smaller flats are useful for those who can’t lift heavy objects. By early June, the plants will be as tall as the cartons, and some varieties will be blossoming. Transplant them as soon as the weather and garden are ready.

A tomato plant is set in a hole dug in the garden, and the milk carton is gently slid up as the hole is backfilled with soil.

Melons, cucumber and squash don’t like to be transplanted, so we sow seed directly into half-gallon containers. Their roots grow rapidly, making timing more important than with the nightshades.  We start melons, cucumber and squash about 14 to 21 days before we’re ready to set them in the garden. Squash and pumpkins will be ready before melons and cucumbers. These plants need go into the ground when their roots start to mat on the bottom of the container. Because the plants dictate when they must go into the ground, it’s better to start cucurbits too late in the season than too early, or we sow successive crops one week apart and just use the ones that are at the right stage of growth when the outside temperature is warm enough.

Because the plants have ample room to grow, nightshades can remain in the hot house until the garden soil is warm and the weather has settled. As plants mature, their roots reach the bottom of the cartons and begin to grow into adjacent cartons. This can be disastrous, especially with cucurbits, so when it begins to happen, we spread the cartons out. We remove the cartons from the wood flats and space them several inches apart on the plywood on top of the compost pile, so the roots are air pruned and plants can be set in the garden without being set back by cutting or ripping the roots.

Eggplants grown in milk cartons are set in coldframes. Sides of the cartons were slit almost to the bottom, and the cartons were gently lifted after the plants were placed in the transplanting hole, which was backfilled with garden soil. The folded tops of the carton serve as a label, deter cutworms and reflect sun. The tops of the coldframes will stay on for a while after transplanting.

We transplant into the ground without disturbing roots by turning the milk carton into a protective collar.  First, by gently squeezing the cartons, we release the root mass from the sides of the carton.  Then, with a sharp knife, we cut the sides of the cartons to within an inch of the bottom. After lowering the carton into a pre-dug hole, we carefully slip the carton up and away from the roots, filling with garden soil as we go and taking care not to disturb the roots.  Finally, we flatten the “flaps” and have a nicely labeled, undisturbed plant, ready to grow without interruption.

About the authors: Adam Tomash and June Zellers garden on a 1.4-acre suburban plot in West Gardiner and have resided in Maine since the early 1970s, gardening in the coldest parts of the state. Not content with the short growing season, they have both worked for the last 30 years to improve techniques for growing heat-loving vegetables organically and now grow even the most demanding crops with consistent success. Tomash was one of the first MOFGA-certified growers in Maine, selling at farmers’ markets and coops for many years. June is a co-coordinator for the volunteer tent and Adam is an exhibition hall co-coordinator for the Common Ground Country Fair.

Reemay covers cucurbit transplants. Tomato transplants, trellised on the right, were watered in with Root Shield and then were mulched.

This article is provided by the Maine Organic Farmers and Gardeners Association (MOFGA), PO Box 170, Unity, ME 04988; 207-568-4142; [email protected]; Joining MOFGA helps support and promote organic farming and gardening in Maine and helps Maine consumers enjoy more healthful, Maine-grown food. Copyright 2007 by the Maine Organic Farmers and Gardeners Association.

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