How to Make Your Own Seed Starting Mix

​If you start a lot of your own seeds, as I do, it may be helpful to make your own seed-starting mix. You can buy small bags or bricks of seed-starting mix, but I have a hard time finding larger bags locally, so I end up buying quite a few small bags each year. Last year, I experimented with making my own seed-starting mix, which worked well enough that I used it again this year. So far, I have again been getting great germination and growth.

​I calculated a rough price for my mix and compared it to the cost of the pre-made bags. It was about the same or even a little more for the make-your-own mix. However, I think the make-your-own mix is superior because the worm castings or compost add nutrients like nitrogen, but not so much that it burns the seedlings, and the addition of perlite and vermiculite helps with drainage and water retention. However, if you wish to save money, you can use a cheaper compost than worm castings or even skip it entirely, as seedlings do not need much nutrition the first couple of weeks they grow. You can always use a liquid fertilizer when necessary.

​I also make a large batch at a time, usually enough to get me through the season without having to open a new bag every few days. With seed-starting mixes, you can choose a peat- or coco coir-based mix. Canadian peat moss is more sustainable than most other peat, so I buy that. Some people prefer coco coir, but you need to buy a reputable brand, as some can have high salt levels that need to be rinsed out by either the manufacturer or consumer after purchase.

Seed Starting Mix

​5 gallons (20 quarts) of coco coir or peat moss
8 quarts perlite
8 quarts vermiculite
4 pounds worm castings (mushroom compost or other types of compost would also work here)
¼ cup pelletized lime (if using peat moss, dissolved in water)

​I based this mix on the bag sizes available at my local gardening store (for example, perlite, vermiculite, and worm castings all come in the amounts listed above). If you can easily access bags of different sizes, you can adjust the recipe or add a little more or less depending on what you can find. I purchase a large bag of peat moss and measure the amount needed using a 5-gallon bucket. So, each compressed bag of peat should make at least three batches of this seed-starting mix. Peat moss is acidic, so lime is added (lime is basic). Lime should not be necessary if you use coco coir instead of peat. I like to dissolve the lime in water before I add it to the other ingredients, so it mixes in more evenly.

​Altogether, this makes a 6-gallon batch of seed-starting mix, so make sure you have a big enough container to mix it in or cut the recipe down. If you wish to adjust this recipe to make your own potting soil mix for transplanting the seedlings, I recommend increasing the compost and decreasing the peat moss or coco coir by the same amount, so there are more nutrients available for the growing plants.