If you make a plentiful supply of good compost, you can screen it to remove large particles and be self-sufficient in seedling and potting compost. In the summer months, compost piles work fast. If you can set aside some time before cold weather to screen the amount of compost you will need for seedlings in the spring, you can then have unfrozen compost ready to use when you need it in January or February.
Even better, if you put the screened compost into some kind of bin, bed or box in your greenhouse, you can transplant lettuce into it, and the watering to keep the lettuce growing will help the compost organisms to mellow out the compost over the winter.
Worm eggs will hatch out, the lettuce roots will make air channels throughout the bin, and you can harvest the lettuce before you need to sow seedlings.
Making Compost Screens
There are two basic styles of compost screen. We make flat frames that fit over a wheelbarrow, and screen into the barrows. Another approach is to make a free-standing frame and throw compost at it, so that it (to some extent) screens itself. Then you shovel the compost into a wheelbarrow. Each type has its advantages.
To make a flat compost screen, cut two sets of battens and make two frames that will sit on top of a wheelbarrow. Then cut some rat wire (hardware cloth), sandwich it between the two frames and bolt the sandwich together. This method makes it easy to switch to new wire when the old piece wears out.
Alternatively, make one frame and staple the hardware cloth to it, for a less durable frame. For a free-standing frame, study the photo.
Free-standing compost screen in use. Photo by Beth LeaMond
A third alternative would be a flat screen suspended at all four corners from a swing-set frame or a convenient horizontal tree limb. Put a tarp on the ground and shuffle the frame as archeologists do when sifting through soil.
Using the flat screens on wheelbarrows feels a bit like doing archeology, with the advantage that the compost lands in the wheelbarrow and doesn't need to be shoveled back up off the ground.
How to Screen Compost
I'll tell you how we use the flat screens on wheelbarrows, as that's our favorite. We have a special collection of compost-screening tools, which are mostly regular hoe heads on short handles. Some people use the Korean Ho-Mi tool for this task. You are looking for a comfortable hand tool that will not destroy the wire.
Shovel a modest amount of compost onto the screen at one end. Use the tool to push the compost back and forth so that the small particles fall through and the bigger pieces stay on the screen. It's important not to scrape the compost back and forth, as the metal tools can break up the wire quite fast. Try to minimize direct contact between the tool and the wire.
We then move any rocks from the screen into buckets with holes in the bottom. Our rock buckets can sit around for months collecting rocks, and having holes in the bottom lets the rain drain out. Another holey bucket collects up any woody materials or undigested compost materials, to go back for another chance at being composted.
Using the flat compost screen on a wheelbarrow. Photo by Wren Vile
It helps to have fairly dry compost for screening. If it's too wet, you can set some to dry on top of the screen, and do some other work for a few hours. In very hot summers, we have even erected a canopy over our screening site, top make the job more pleasant.
We use a large amount of compost, so this job takes us days. It's a job we fit in around more urgent tasks, over a period of weeks. Our greenhouse has beds built of loose-fit cinder blocks, and we set up boards across the tops of the beds, so we can get to the far end of the greenhouse. It's a challenge at first to stay on the boards, but the worst that can happen is to tip the barrow and fall 18 inches off the boards!
Our greenhouse is designed for spring seedling production. We don't grow anything there in summer — it's empty down to the concrete floor. For a smaller operation, you can simply fill any series of bins or tubs or boxes inside your greenhouse. Get them in position near the windows before you fill them.
Growing Winter Greenhouse Lettuce
When the bins are full, water the compost enough to keep it damp and alive until you transplant your lettuce. We transplant ours in early October (our first frost is mid-October). Use cold-hardy leaf types or romaines.
If you are ready a long time before winter lettuce transplanting time, you could perhaps grow a different short-term crop in the compost first. You can harvest outer leaves from the lettuce whenever they are big enough, all winter long. Then start to clear them when you need to use the compost for seedlings.
Young lettuce plants in greenhouse beds in October. Photo by Bridget Aleshire
Using Homemade Compost for Seedlings
We start our seedlings in mid-January, although we only sow a few things the first week, and harvesting one or two lettuces would clear enough compost for those flats. We do not mix any other ingredients with our compost when we use it for sowing seeds, or for potting up transplants. We make great compost and it serves us well. The plants grow big and strong.
The only issue we sometimes have is aphids, which we deal with by gathering up lady bugs, or if numbers of aphids per ladybug are too high, we use a soap spray. It's certainly nice to know what our plants are growing in, and not to be lugging bags of mix back from the store.
Pam Dawling manages the vegetable gardens at Twin Oaks Community in central Virginia. She often presents workshops at MOTHER EARTH NEWS Fairs. Pam also writes for Growing for Market magazine. Her book, Sustainable Market Farming: Intensive Vegetable Production on a Few Acres, is available in the MOTHER EARTH NEWS Store. Pam's blog is on her website and also on Facebook, and read all of her MOTHER EARTH NEWS posts here.
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