Sphagnum peat moss, perlite and vermiculite
Garden of Eatin', How-To, Seeds & Seedlings

How to Make Your Own Seed Starting (and Potting) Mix

Now that you’ve made your own recycled newspaper pots, it’s time to fill them up. If you plan to grow a lot of seedlings, making your own seed starting mix is a snap and it can be used as a basis for potting mix after. Even if you only need a small bag for your windowsill tray, you can refer to these ingredients as a guide for buying a commercial seed starting mix.

Certain store-bought mixes contain synthetic fertilizers and wetting agents, which defeat the purpose of growing organically. Seed starting only requires a minimal soilless mix, as seedlings do not need fertilizer until they develop their first “true set” of leaves. When the true leaves emerge, you can supplement the mix with your own organic fertilizer. After all, it’s always good to know what’s going in your garden — and eventually, your food.

Seed Starting Mix

  • 1 part sphagnum peat moss (or coir)
  • 1 part perlite
  • 1 part vermiculite

A “part” refers to any unit of measurement to make the quantity you need, as long as it’s consistent: a scoop, a bucket, or a bag of each ingredient.

Mix equal parts of all ingredients together

Combine all ingredients in a clean tub or bucket, and water down the mix. It should be moist, not soggy. This initial watering makes it easier to keep the mix uniformly moist throughout the seed starting period, as sphagnum peat moss can be difficult to re-wet if it’s been left to dry out in a pot.

Fill your pot with seed starting mix

Sphagnum peat moss (not to be confused with the coarser and more fibrous sphagnum moss that’s typically used to line floral baskets) is an excellent, sterile, moisture-retaining medium. Coir is similar to sphagnum peat moss in terms of look, feel and retention, but is made from the fiber of coconut shells. Perlite is an ultra lightweight volcanic glass resembling white popcorn ceiling, and provides drainage and aeration. Vermiculite is a natural micaceous mineral, brownish and granular in appearance, with water-absorbing properties that facilitate re-wetting of the soilless mix.

Fill your seedling pots with this homemade mix, add seeds, and sprinkle a thin layer of vermiculite over your seeds if they need to be covered.

Fill your pot with seed starting mix

If you have ingredients left over, you can save them for next season, or make a potting mix for your transplants.

Basic Potting Mix

  • 6 parts sphagnum peat moss (or coir)
  • 1 part perlite
  • 1 part vermiculite

Enriched Potting Mix

  • 4 parts sphagnum peat moss (or coir)
  • 2 parts compost
  • 1 part perlite
  • 1 part vermiculite

You can take it even further by amending your potting mix with bone meal, blood meal, lime, and a host of other supplements, depending on the nutritional needs of your plants. But if you’re more gardener than chemist like I am, it’s fine to keep it simple and just supply your plants with a lot of old-fashioned love, sunshine, and water.

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