Anyone who has ever grown tomatoes, peppers or basil from seed knows that magical moment: the small green sprout pushing its way through the soil. And then – nothing. The seedlings remain small, turn yellow, keel over, or fall victim to the dreaded damping-off disease.
Usually, it's not the seeds. It's the soil.
Ready-made potting soil from the hardware store sounds practical – and it is, up to a point. But many commercially available products are too rich in nutrients for delicate seedlings, poorly aerated, or prone to compaction. The result: roots that don't get air, waterlogging that promotes fungal diseases, and seedlings that never really take off.
The good news: mixing your own potting soil is easier than you think – and you know exactly what's in it. With the right ingredients, including zeolite as the secret star, your young plants will get the best possible start in life.
What good seed-starting mix must do
Before we start mixing, a quick theory – I promise, only the essentials.
A good seed-starting mix for sprouts and young plants must be able to do several things at once:
Be loose and airy. Germinating seeds and young roots need oxygen. A compacted soil is almost as bad as no soil at all for them.
Retain moisture, but not become waterlogged. This is the trickiest balancing act. Too dry – and the seedlings die. Too wet – and fungi take over.
Be low in nutrients. This sounds counterintuitive, but seedlings initially need hardly any nutrients. They live on what is stored in the seed. Too many nutrients burn delicate roots or promote excessive leaf growth at the expense of the roots.
Have a fine and uniform structure. Coarse clumps or pieces of wood hinder germination and root growth.
Sounds contradictory? It isn't – if you use the right ingredients in the right mix.
The basic ingredients for homemade seed-starting mix
Coco coir or mature compost – the base
Coco coir (coconut fiber) is an excellent base for seed-starting mixes. It is light, structurally stable, retains moisture well, and is naturally largely nutrient-free and sterile – ideal for sensitive seedlings. It is also a byproduct of coconut processing, making it a sustainable alternative to peat.
Alternatively, you can use well-rotted, fine compost – but make sure it is truly mature. Fresh or semi-finished compost contains too many nutrients and can introduce fungi and pests.
Proportion in the mix: approx. 50–60%
Perlite or sand – for drainage and aeration
Perlite are expanded volcanic glass bubbles – super light, sterile, and excellent for aeration. They prevent the soil from compacting and ensure that excess water can drain away.
If you don't have perlite on hand, you can also use coarse quartz sand – but please, no fine play sand, as that tends to make the soil denser.
Proportion in the mix: approx. 20–30%
Zeolite – the water buffer and nutrient reservoir
And now comes the part that makes all the difference: BODENKRAFT PUR, our activated zeolite in fine grit.
Why zeolite in seed-starting mix? Because it solves the most common problem when growing young plants: uneven moisture.
Zeolite stores water in its porous structure and releases it slowly – meaning the soil won't dry out in a flash if you can't water for a day. At the same time, zeolite prevents waterlogging because it absorbs excess water but doesn't hold onto it like an unwrung sponge.
For seedlings, this means: consistent moisture, without the risk of fungal diseases or root rot. This is invaluable, especially in the critical phase between germination and the first true leaves.
Another advantage: zeolite can bind small amounts of nutrients like potassium and calcium and release them in a buffered way – exactly when the young plant begins to depend on external nutrient sources.
Proportion in the mix: approx. 10–20%
Optional: Basalt flour – for basic mineral supply
If you want to give your young plants a mineral foundation, you can add a small amount of basalt flour. Basalt contains trace elements such as iron, manganese, and zinc, and also improves soil structure long-term.
For a pure seed-starting mix, basalt flour is optional – but if you later repot the plants into larger pots or into the garden bed and use fresh soil, a small addition is worthwhile.
Proportion in the mix (optional): 5–10%
The finished recipes – simple and practical
Recipe 1: Universal seed-starting mix for vegetables & herbs
This mix is suitable for almost everything – tomatoes, peppers, zucchini, basil, parsley, lettuce, etc.
• 3 parts coco coir
• 1 part perlite
• 1 part BODENKRAFT PUR (fine grit)
Mix everything well, moisten slightly (the soil should feel damp, but no water should be squeezed out), and you're done. Before filling the seed-starting pots, rub it through your hands again briefly to remove any clumps.
Recipe 2: For sensitive seedlings (celery, chili, pepper)
Some plants are particularly sensitive when germinating – they need an even looser, finer mix.
• 3 parts coco coir
• 2 parts perlite
• 1 part BODENKRAFT PUR
The higher perlite content provides extra aeration. Ideal for plants with a long germination time that spend more time in moist soil.
Recipe 3: Seed-starting and pricking out soil in one (for self-sufficient gardeners)
If you need a mix for both starting seeds and later pricking out, you can mix a slightly more nutrient-rich version:
• 2 parts coco coir
• 1 part mature compost
• 1 part perlite
• 1 part BODENKRAFT PUR
• Optional: a small handful of basalt flour
This mix is suitable from germination to transplanting into the outdoor garden bed – you save yourself the hassle of changing the soil when pricking out.
Common mistakes when mixing your own – and how to avoid them
Too wet soil when filling. The mix should be moist, but not wet. Test it like this: take a handful, squeeze it – it should hold its shape, but no water should come out.
Too large pots for small seedlings. In pots that are too large, the soil around the small roots stays wet for too long – risk of fungus. Start with small seed-starting pots or multi-cell trays and only repot once the plant has rooted well in the pot.
Incorrect storage of the mix. It is best to use homemade soil fresh or store it dry and airy. Undesirable organisms can quickly form in a closed, damp bag.
Fertilizing too early. Seedlings need almost no fertilizer in the first few weeks. Only when the first true leaves appear and the plant begins to grow actively can you start with a very weak dose of fertilizer.
Step by step: Growing with homemade soil
1. Prepare the mix – measure ingredients according to the recipe and mix well. Moisten slightly.
2. Fill pots – do not press too firmly, the soil should remain loose.
3. Lay out seeds – depth according to seed (usually 1–2× seed diameter deep).
4. Water gently – preferably with a fine spray or from below (place pots briefly in water).
5.Cover – with cling film or a lid until the first seedlings appear.
6. Place in a bright and warm spot – most vegetable seeds germinate best at 18–24 °C.
7. Remove cover as soon as the first seedlings are visible – now they need air.
8. Keep evenly moist – thanks to zeolite in the mix, you'll need to water less often. It's better to water less frequently and thoroughly than a little bit every day.
The difference you will see
Once you've started seeds with homemade soil and zeolite, you won't want to go back. The seedlings appear stronger from the start, the roots develop more evenly, and the stress from over- or under-watering is significantly reduced.
This is not magic – it is because the soil does exactly what it is supposed to do: buffer water, allow air to pass through, and enable the seedlings to get a stable start.
You can find BODENKRAFT PUR in our shop – in the fine grit that is ideal for seed-starting mixes. And if you have questions about the right amount or mix, please contact us. We'll help you give your young plants the best start.
→ You can find suitable STEINKRAFT products for your garden in our Garden Collection.
Happy growing – and may your seedlings sprout strong and healthy! 🌿
About the Author
Michaela Schirmbrand-Pfeiffer is an entrepreneur, coach, and co-founder of STEINKRAFT. Her passion: the potential of people and the earth alike. She believes that the earth unfolds itself – if we give it the right space. In her garden blogs, she shares knowledge that enables better decisions: for healthy soil, nutritious food, and a life in harmony with nature.
