This post contains affiliate links, learn more here: Disclaimer Spring is on the way and it’s almost time to start seedlings. I’ve been experimenting for over 6 years and I’ve created The Best DIY Seed Starting Mix, well at least in my opinion. This mix performs so well that I just had to share it with you. But first I will share with you a few of my failures and why I feel other seed starting mediums didn’t work for me.
First, what I don’t like to use in my Soil Mix:
While many people have been using the following ingredients with great success over the years, in my experience opting for a custom blend of seed starting mix over using the following as stand-alone ingredients just seems to produce far better results.
Peat Moss or Peat Pots
Peat moss and peat pots are a very traditional medium for seed starting. I have chosen not to use peat as the main ingredient in our seed starting mix because it’s really not a renewable resource and it’s far less nutrient-rich than other mediums; also I find it dries out too quickly. Peat is hard to avoid in the garden world and I do inherently have some in my mix, but it’s not my main ingredient.
All my friends know how much I love homemade compost, but I’ve learned over the years that homemade compost is not the best medium for seed starting. The inputs, microbes and moisture holding in homemade compost are too unpredictable for young seedlings and can often lead to poor germination and diseases such as dampening off.
Dampening off is when the seedling rots just at the soil level, killing the seedling. This can be very disheartening when you have waited patiently up to 21 days for your seeds to germinate, only for them to fall over and die. 🙁
So those are 2 the key products I avoid when making my soil mix. I have also chosen to avoid manure, coconut coir and those compressed, netted peat pods (the netting never breaks down in my soil). Do you love these common products? Or are they on your no-go list too?
So what’s my super-duper, secret, seed starting mix??
I use a blend of a few store-bought mediums to create my seedling mix, the reason that I use store-bought ingredients is because I know the products are of a consistent quality and have been heat-treated to ensure the mediums do not contain fungus, insects, weed seeds etc. Trust me, when you spend as much money on seeds each year as I do, you want to protect your investment and ensure your seeds get off to the best start possible.
Ok, my soil mix recipe is simple, I will outline it below then go into a bit more detail about why I have chosen each ingredient.
The Best DIY Seed Starting Mix:
45% Indoor Potting Soil, do your best to get Organic or All Natural
45% Seed Starting Mix, again Organic/All Natural is best
10% Worm Castings, a little goes a long way with this expensive ingredient
A sprinkle of Green Sand or other all-natural soil mineral amendment
Add a bit of water as you mix your ingredients, this will give you a truer volume and keep the dust down.
HEY! What kind of measurements are those!?
Each of us will have different volume requirements if you are just doing a tray at a time use these ratios:
4.5 cups Potting Soil
4.5 cups Seedling Mix
1 cup Worm Castings
1 tsp Green Sand or other all-natural mineral amendment
If you are doing a wheelbarrow full measure in 5-gallon buckets. Oh, and again, be sure to add a bit of moisture as you mix your ingredients.
4.5 gal Potting Soil
4.5 gal Seedling Mix
1 gal (an ice cream pail) Worm Castings
1.5 cups Green Sand or other all-natural mineral amendment.
So why did I chose these ingredients over ones for my seed starting mix?
Indoor Potting Soil
Indoor Potting Soil is light and fluffy and has excellent moisture holding capacity, it often contains vermiculite or perlite which encourage airflow within the soil. Indoor Potting mix is also less expensive than other mediums which makes it a great filler ingredient.
Seedling Mix is a very duffy/fluffy medium and often contains a blend of peat and other ingredients. Seedling Mix is very light which makes it easy for young roots to grow deeply in search of moisture and nutrients. But it can be more expensive than potting mix which is why I like to blend it.
Worm Castings or Worm Compost
Worm Castings are the living/biological component of my starter mix. I find that when we take the time to add worm castings, even in such a small dose, the plants respond unbelievably well. We have had such great results by adding worm castings that we have chosen to delay our seed starting by a month this year; last year the tomatoes grew so fast that I had to pot them up three times before it was warm enough to start setting them outside!
I like to add a small pinch of mineral soil amendment, this is usually sold in garden stores as “Green Sand“. Many soils are lacking in trace minerals, so by adding Green Sand, you are essentially giving your seedlings a multi-vitamin. All companies blend their Green Sand differently but it usually contains a balanced mix of alfalfa, potassium, glacial rock dust and other natural ingredients. Green Sand not only contains your classic N-P-K but also contains important trace minerals such as calcium. A little goes a long way, I would suggest using 1-2 tsp per 4 cups of soil mix.
If you are in Canada, my first choice is Gaia Green All-Purpose Organic “Fertilizer”, this is not really a fertilizer as much as it is a soil amendment. Gaia Green is made in Grand Forks, BC and it is amazing stuff.
So there you have it.
My secret soil mix for starting happy, healthy, robust seedlings.
For more ways to get gardening now, check out my other Gardening Articles including Tips and Tricks For Starting Seeds Indoors and if you liked this please share the love: comment, share and tell your friends 😉
Thanks for hanging out!