How to Make Seed Starting Mix

It’s still too early to start seeds indoors in Minnesota, with the exception of onions, but many gardeners are thinking about their seed-starting set up. While many excellent commercial varieties of seed-starting mix are available in garden centers, gardeners who start a lot of plants from seed or want to control all the elements of their seed starting may want to make their own seed starting mix.

There are an abundance of recipes for seed starting mix, but all of them contain three basic elements.

  • Peat moss or coconut coir. These products help retain moisture, an essential element for seed starting. Some gardeners don’t like to use peat moss because of environmental concerns about the loss of the Canadian bog lands where most of it is mined. In researching this blog post, I found one gardener who recommends leaf mold as a replacement for peat moss, but leaf mold mulch is not generally available in stores.
  • Perlite or vermiculite or both. Perlite is volcanic ash that has been heated until it pops. It looks a bit like tiny popcorn grains or styrofoam. Vermiculite is a mined mineral. The individual grains of each of them are larger in size than normal garden soil, so they help keep a seed starting mix aerated, another essential for germination and growth.
  • Compost or worm castings. These elements add nutrition for the growing plants. Seeds themselves don’t need any nutrition — they have everything they need to germinate right inside. But, if you plan to keep your plants in their original seed starting containers for a few weeks, it’s good to have something for the roots to grow on.

Some mixes add other ingredients, such as horticultural lime, which neutralizes the acid in peat moss, or greensand, a fertilizer that contains additional minerals from the ocean.

DSCI0036The proportions of these ingredients vary widely among those who make seed starting mix. Some add as much as 50 percent compost or worm castings, while others go much lower. The mix I have made in the past that has worked very well for seed starting includes 20 percent worm castings. Generally, the peat/coir and perlite/vermiculite are equal parts of the remainder of the mix. So, the mix I use, which originated here, includes two parts peat moss, two parts vermiculite and one part worm castings. (A part can be anything — a cup, a bucket, a gallon — depending on how much your are making.) With seed starting, I do not add any extra fertilizer until the seeds have germinated and have a few sets of leaves. Then, I will fertilize with a dilute solutions of fish emulsion and water.

What do you use to start seeds indoors?

—Mary Lahr Schier

 

 

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