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When I start my seeds each year, I like to make sure they have everything they need to grow strong, healthy roots and sturdy stems. While a good seed starting mix (like my DIY coco coir-based mix) provides the right texture and moisture balance, young seedlings also need gentle but effective nutrition to thrive. That’s where my homemade seed starting fertilizer comes in.
Unlike mature plants, seedlings don’t need heavy doses of fertilizer. Instead, they need a balanced mix of essential minerals and nutrients to encourage steady, healthy growth without overwhelming their delicate roots. I’ve fine-tuned my recipe over the years to create a natural, slow-release blend that provides seedlings with everything they need—without the risk of burning or overfeeding them.
In this article, I’ll walk you through my go-to seed starting fertilizer recipe, explain the benefits of each ingredient, and show you how to use it for the best results. Let’s get started!
Why Seedlings Need the Right Fertilizer
When seeds first sprout, they rely on the nutrients stored within the seed itself. But once they develop their first set of true leaves, they start needing extra nourishment to support strong roots, sturdy stems, and healthy leaf growth. That’s where seed starting fertilizer comes in.
Unlike fertilizers for mature plants, a good seed starting fertilizer should be gentle, balanced, and slow-releasing. Young seedlings have delicate roots that can easily be damaged by synthetic or overly strong fertilizers, so I prefer using organic, mineral-rich ingredients that provide steady nutrition without overwhelming them.
Another reason I make my own fertilizer? Control. Commercial seed-starting fertilizers often contain synthetic additives or unnecessary fillers, and I like knowing exactly what my plants are getting. By creating my own mix, I can ensure that my seedlings get the perfect combination of nutrients right from the start.
Now, let’s take a look at the key ingredients I use in my homemade seed starting fertilizer and why they work so well.
Ingredients for Seed Starting Fertilizer
I like to keep things simple when it comes to fertilizing my seedlings, and this dry powdered seed starting fertilizer is the perfect addition to my coco coir seed starting mix. Instead of feeding seedlings with liquid fertilizers later, I mix this blend directly into the soil when I prepare my seed trays or soil blocks. That way, the nutrients are evenly distributed, giving young plants a steady, gentle supply of essential minerals as they grow.
Here’s what I use in my seed starting fertilizer and why:
Azomite – A Boost of Essential Trace Minerals
Azomite is a natural rock dust packed with over 70 trace minerals that plants need for healthy development. Seedlings don’t require large amounts of nitrogen or phosphorus at first, but they do need micronutrients like calcium, magnesium, and zinc to build strong cell walls and prevent deficiencies. Azomite provides those in a slow-release form, ensuring a steady supply of minerals as seedlings grow.
Green Sand – Long-Lasting Potassium Source
Green sand is a fantastic natural source of potassium, which is essential for strong roots and disease resistance. It also loosens compacted soil and helps improve moisture retention—both of which are useful in a coco coir-based mix. Unlike synthetic potassium fertilizers, green sand releases nutrients slowly, making it perfect for seedlings that need gentle, ongoing support.
Blood Meal – A Gentle Nitrogen Boost
Nitrogen is essential for leaf and stem growth, and blood meal provides a slow, natural source of it without overwhelming delicate seedlings. Since coco coir is naturally low in nitrogen, adding a small amount of blood meal ensures that young plants get the early boost they need to develop lush, green leaves.
Bone Meal – Phosphorus for Strong Root Development
Phosphorus is the key to healthy root systems, and bone meal is one of the best organic sources. Since seedlings depend on their roots to take up water and nutrients, adding a little bone meal to the mix helps them establish deep, sturdy root networks that prepare them for transplanting.
Biochar – Improves Soil Health & Retains Nutrients
Biochar is one of my favorite additions to any soil mix. It acts like a nutrient sponge, holding onto minerals and moisture so they’re slowly released over time—perfect for young seedlings. Biochar also improves soil structure, aeration, and microbial activity, which makes it especially useful when working with coco coir.
By combining these ingredients into a dry powdered seed starting fertilizer, I ensure that my seedlings have a balanced, slow-release nutrient source mixed right into their soil. Now, let’s go over the exact recipe and how I mix it into my coco coir seed starting mix.
My Go-To Seed Starting Fertilizer Recipe
This dry powdered seed starting fertilizer is easy to make, and I love that I can mix up a big batch and have it ready for whenever I’m preparing seed trays or soil blocks. Since it’s blended directly into my coco coir seed starting mix, it provides a steady, slow-release source of nutrients that seedlings can access as they grow.
Understanding “Parts” in a Recipe
When I list ingredients in parts, it simply means that the ratio stays the same no matter how much you make. For example, if you use 1 cup as your “part,” the recipe would be:
- 4 cups Azomite
- 2 cups green sand
- 1 cup blood meal
- 1 cup bone meal
- 2 cups biochar
If you want to make a smaller batch, you could use 1/2 cup as a part, and if you need a large batch, you could use 1 quart per part. The key is keeping the proportions the same.
Ingredients:
- 4 parts Azomite (for essential trace minerals)
- 2 parts green sand (for slow-release potassium)
- 1 part blood meal (for a gentle nitrogen boost)
- 1 part bone meal (for strong root development)
- 2 parts biochar (to improve soil health and nutrient retention)
How to Make & Use This Fertilizer:
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Measure & Mix the Ingredients
I use an extra large jar or a bucket to combine all the ingredients. Since these are dry powders, I make sure to wear gloves and mix everything thoroughly, so the nutrients are evenly distributed. -
Store in an Airtight Container
If I’m making a big batch, I store the fertilizer in a sealed container or glass jar to keep it fresh. Since these ingredients don’t break down quickly, a single batch lasts me a long time. -
Mix It Into My Coco Coir Seed Starting Mix
When I’m preparing my seed starting mix, I add 2/3 cup of this fertilizer per batch of soil mix and stir everything together well. This ensures that every part of the mix has a balanced supply of nutrients before I start planting my seeds.
Since this fertilizer is slow-releasing, I don’t have to worry about overfeeding or burning delicate seedlings. It provides just the right amount of nutrients from the start, so I rarely need to add any extra fertilizer until the seedlings are ready for transplanting.
More Gardening Articles to Explore
If you’re passionate about growing healthy plants naturally, be sure to check out my other articles on coco coir, composting, and gardening:
- What Is Coco Coir? A Sustainable Peat Moss Alternative
- DIY Coco Coir Seed Starting Mix Recipe
- Harmony with Nature: The Power of Permaculture Gardening for Sustainability
- 10 Easy Permaculture Projects for Beginners
- The 6 Basics of Permaculture Design: Sustainable Gardening
- Hugelkultur: An Amazing Permaculture Gardening Technique
- The Best Guide to Planning a Raised Bed Garden
- 3 Cheap and Easy Ways to fill a raised garden bed
- Composting 101: An Easy Composting How To Guide
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