DIY 4-Ingredient Soil Mix Recipes

Growing Seeds with Soil Mixes

A seed, in and of itself, is miraculous. Seeds symbolize hope, new life, a new year, and new beginnings. Growing plants from seeds are a satisfying and cost effective way to add new plants, diversify what you grow, and expand the garden space. In fact, some amazing vegetables (especially tomatoes) are only available from seeds. I want to share a 4-ingredient seed starting recipe that has been successful during my years as a gardener, both in the greenhouse and my home garden. I’ll also share my earth-friendly potting soil recipe using natural materials from the outdoors. I’ll discuss why these mixes work based on the science of how plants grow. This understanding will make growing from seed more efficient in time and money.

A Seed is the Ultimate Survival Warrior
Legume seed germinating

Legume seed germinating. The emerging embryonic root grows downward where its tip (root cap) propagates and multiplies via specialized embryonic cells. Roots absorb nutrients.

A seed contains an embryo (baby plant), food (endosperm), and a seed coat. It has everything it needs to germinate and to grow under the right conditions. I have germinated seeds in soilless mediums, compost, vermiculite, and even wet paper towels. One day when I was washing dishes, I noticed a butternut squash seed had germinated next to my sink’s drain under my dish-drying rack! (That roasted butternut squash was delicious!) Viable seeds are living entities; the ultimate survival warrior. For example, National Geographic reported a 32,000 year old seed was recovered under permafrost in Siberia. Scientist extracted viable tissue within the seed and grew a wildflower that existed during that time period. Amazing! 

Which Came First: The Plant or Seed?

Similar to how chickens hatch out of eggs, plants ‘hatch’ out of seeds. This process is germination. The most critical time of a plant’s life is when it’s a baby; makes sense because all animals and plants are vulnerable as babies. Gardeners use seed starting mixes to provide tender, loving care for seedlings (baby plants).

Seed Starting Recipe

  • 4 parts screened compost
  • 2 parts coconut coir or peat moss
  • 1 part perlite
  • 1 part vermiculite
Left: Seed starting mix ingredients (from top to bottom) are compost, peat moss, perlite, and vermiculite. Right: Seeding starting mix.
Benefits of DIY Soil Mixes

A seed starting mix provides a fine-textured seedbed and seed-to-soil contact to ensure optimal germination and moisture consistency. With some planning and scheduling, starting seeds indoors provide a jump start to the growing season. Vegetables, such as peppers, grow well in seed starting mixes because they take a longer time to germinate. Their seedlings also grow at a slower rate. Making mixes from scratch allows you to alter them. For example, I use less compost in the top layer of my mix when sowing tiny seeds such as bee balm. You don’t have this flexibility when you buy pre-made mixes.

Bang For Your Buck

You could buy a $5 (8-quart size) bag of pre-made seed starting mix at a big box store. You’ll soon realize how very little you get for the money. Buying bulk offers a considerable lower cost per volume. Bulk sizes of perlite, coir/peat moss, and vermiculite range from 2 to 4 cubic feet with prices from $15 to $25 each. That’s approximately $50 to $75 for 3 ingredients (which may seem pricey up front) but they have long shelf life and will last the average gardener several years worth of seed starting ingredients. They are also beneficial for plant propagation which equates to more free plants! Prices for compost vary since you can either make it or buy it. The compost should be of high quality with an earth-pleasing smell and crumbling texture.

Ingredient #1: Compost

You may have found this blog by googling ‘seed starting recipe’ and are comparing recipes. Mine includes compost while others may not. I will discuss the reasons why soilless seed starting mix may actually require more work, time, material, and money. 

What would Mother Nature do? This question is asked in my blogs because it serves as the premise of my Web site. In nature, when seeds drop to the ground (usually in autumn) many land on fallen leaves or are covered by leaves. During winter and into spring, the leaves decompose and return organic matter back to the earth. As temperatures warm, seeds germinate within the leaf compost. This compost provides nutrients and for good reason.

Seedling with cotyledons that germinated in leaf compost. Zoom in to see emerging true leaves.

The food stored in a seed (endosperm) supports the developing baby plant (embryo) for only so long. Some academic studies have estimated endosperm lasts 2 weeks after germination but it’s dependent on the plant species. A seed’s endosperm develops into cotyledons, the first set of green leaves. In fact, the whole microgreen industry revolves around the cotyledons of edible plants! As the stored food (cotyledon) depletes, the plant must intake food from its newly developed true leaves (photosynthesis) and nutrients from its roots. The true leaves are like the mini-me of the adult leaves. The presence of true leaves also signals roots are actively seeking nutrients. This transition is a critical time of a plant’s life. Using a seed starting mix that includes nutrients such as compost nourishes the developing root system immediately.

Ingredient #2: Coconut Coir or Peat Moss

Maintaining uniform moisture is a primary requirement for growing seeds, hence, why you see peat moss and/or coconut coir in almost every seed germination mix. Both retain water longer, hold nutrients, and increase absorbency in seed starting mixes. Both provide volume and do not compact. There are environmental disadvantages for both. I’ll be honest, I use both peat and coir for seed starting but I try my best to minimize my eco-footprint by using it exclusively for germination only. I do not buy pre-made potting soil mixes either. My earth-friendly potting soil recipe is at the end.

Environmental Impact

Peat moss is the decomposed remains of sphagnum moss found in peat bogs throughout the world. Peat moss takes a long time to form plus it holds carbon which is released when harvested. Coconut coir (also known as coco coir or coir) is the byproduct/coconut fiber of coconut processing. It is more expensive since its shipped from Asia. It requires lots of water for processing (along with polluting that water) which is already a limited resource in India. 

Ingredient #3 and #4: Perlite and Vermiculite

I am bundling perlite and vermiculite together since they both provide aeration and improve drainage in soil mediums. Many soil mixes include a 1:1 ratio for them. Perlite looks like white popcorn. It is man-made and created when high heat is applied to volcanic glass. Perlite absorbs moisture on the exterior of its surface but prevents it from entering inside. That is why it’s useful for providing moisture to plant roots. Perlite provides air chambers in the soil for oxygen. Vermiculite is a naturally occurring crystalline compound that produces flakes of brown, metallic-looking material. It’s also light weight. It retains water moisture for an extended time which benefits plant roots.

Both are readily available at big box stores and garden centers. These retailers offer smaller quart size bags with higher per-volume pricing. You can buy in bulk from commercial nursery or landscaping supply businesses. 

Soilless Mix

Seed germination requires moisture, air, temperature and light. No soil! Therefore, seeds can germinate in a soilless mix using equal parts of vermiculite, perlite, and peat moss (1:1:1). This may be a preferred mix especially if you have limited space. For example, I have germinated 30 tomato seeds in as little space as that of an ice cube using this mix! It’s a lighter medium that drains quicker.

A soilless mix of a 1:1:1 ratio of vermiculite, perlite, and peat moss (or coir)

The downside: peat moss, perlite, and vermiculite offer minimal nutrients compared to compost. You must be on your ‘a-game’ to transplant these seedlings into a nutrient enriched medium. That means more work (your time) and materials (more money) because seedlings need a healthy root system prior to transplanting into the garden. That’s where potting soil mix comes to play. Potting soil mix ($15 for large bags) is intended to grow plants in a pot, a container, or a planter. The mix provides nutrients from fertilizer pellets and soil/compost. Lime, perlite, vermiculite, pine bark, and sometimes unwanted seeds of invasive weeds are included. Potting soil also includes more peat moss, a nonrenewable resource, to assist with water retention and volume. Are you noticing a redundancy of some ingredients?

Earth-friendly Potting Soil Recipe

  • 3 parts compost
  • 1 part seed starting mix
  • 1 part shredded leaves
  • 1 part shredded, decomposed tree mulch (or pine bark)
Left: Potting soil mix ingredients (from top to bottom) shredded mulch, shredded leaves, compost, and seed starting mix. Right: Earth-friendly potting soil

This earth-friendly potting soil mix recycles nature’s bounties. Seeds have germinated in leaf compost for millions of years. So why not use these nutrients instead of synthetic fertilizers? I always set aside fallen leaves during autumn for future use. Compost can be created from kitchen scraps & garden waste. Decomposed tree mulch or pine bark serves multiple uses in the garden. This year, I am using decomposed tree mulch since a tree company took down some trees close to our house. Tree companies may deliver mulch to your home for free to avoid the cost to get rid of it. A word of caution: do not use tree mulch immediately. Allow it to decompose for several months before use. If you reach out to a tree company, then please be careful and do your research. The last thing you want to import is mulch from diseased trees. Similar to my seed starting mix, making potting soil mixes from scratch allows you to alter them. For example, if you have a plant that prefers quick drainage then add more perlite.

Conclusion

The most critical time of a plant’s life is when it’s a baby. Therefore, I try not to rock the cradle too much. I save time, money, and additional handling/transplanting of seedlings when I use a seed starting mix with compost. This helps the plant to develop a robust root system sooner which allows me to transplant it to the garden quicker.

I hope you found this blog useful and my experiences helpful. In Zone 7b, I sow most of my vegetables and flowers outside using my 4-ingredient seed starting mix. My home page will automatically update this year’s seed starting journey so please bookmark. 🙂 If you are on Instagram, then please reach out and connect! I would love to follow your garden journeys. Wishing you and yours a wonderful gardening season!

Published by all.i.plant

Horticulturist with an emphasis on improving biodiversity one yard at time. Organic vegetable and wildlife gardening.

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