Seed compost is a mild compost blend with the proper consistency to provide adequate drainage and moisture levels that promote proper seed germination and root growth. While you can use most types of organic waste to make basic compost for a soil amendment or fertilizer, it takes special ingredients if you want to make seed compost. Nicky Scott, author of the book "Composting: An Easy Household Guide," suggests that you create your own, inexpensive seed compost using a blend of carbon-rich cardboard and nitrogen-rich grass clippings. (See Reference 1) Use hot-composting procedures to ensure the organic waste heats up adequately to destroy any weed seeds that may be present.
Collect equal amounts of waste cardboard and freshly cut grass clippings. Shred the cardboard into little pieces no wider than approximately 2 inches to promote quicker composting.
Spread a 2-inch layer of the shredded cardboard across the bottom of a 3X3-foot compost bin. Spray the layer of cardboard with a light mist of water from your garden hose, dampening it until it has the moisture level of a wrung-out sponge.
Sprinkle the grass clippings loosely on top of the shredded cardboard chunks in a 2-inch layer. Loosen any packed clumps of the grass with your fingers to provide adequate air pockets in the nitrogen-dense green waste.
Top the layer of grass clippings with a second layer of carbon-dense cardboard waste, wetting it down again with water. Repeat with alternate layers of cardboard and grass clippings until the compost bin contains approximately 3 cubic feet of organic waste. Insert a metal rebar pole down through the top center of the pile so you can monitor heat levels. Replace the cover on your bin or cover it loosely with a plastic tarpaulin or sheet of black plastic for heat retention.
Let your compost sit for several days to allow the microorganisms to begin the decomposition process. Pull out the metal post and touch it with your hand; ideally, it should be very warm to the touch. Stir together the layers of damp cardboard and grass clippings to increase air flow in the heap, which will also promote the hot composting process. Replace the metal post to the center of the heap.
Maintain the hot composting temperatures for approximately 14 days by turning the waste daily from that point on. Check moisture levels by squishing a handful of it in your hand; if you can squeeze out more than 2 drops of moisture, it's too wet, and you'll need to add extra shredded cardboard to soak up the excess dampness.
Stir the compost every few days after the first two to three weeks. Monitor the consistency of the waste to determine when it's mature. Ideally, it should smell earthy and have a loosely textured, brown appearance. Allow the mature compost to cool down completely before using it as seed compost.