Thriving houseplants

DIY super soil for houseplants—here’s how to make the perfect mix for each species

Are your houseplants looking unwell? The cause might be unsuitable soil. Discover the requirements of various plant species and create the perfect growing medium for each of them. Enhance bagged soil or mix entirely new substrates using materials like clay granules, vermiculite, bokashi soil, and biochar.

Author Outi Tynys

Images Teija Tuisku

January 16, 2025Lue suomeksi

1. Experiment with mixtures

Experiment with biochar, buckwheat hulls, bark, and vermiculite to find the best growing medium for different plant species and your care routines. Inorganic materials like expanded clay pellets, houseplant gravel, and clay granules are great for both soilless cultivation and enhancing potting soil.

2. Enhance ready-made bagged soil

Ready-made soil mixes, such as flower, cactus, and houseplant soils, are suitable for plants as they are, but they are also easy to customize with both purchased and home-sourced materials. You can adjust the medium’s aeration, drainage, and water retention to meet the preferences of each species.

growing media for houseplants — Bokashi expert **Linda Wirtanen** suggests making a growing medium for houseplants by mixing materials like clay granules, vermiculite, biochar, and bokashi soil.

3. Water correctly

Clay granules, biochar, and vermiculite can significantly extend watering intervals compared to regular potting soil, so it’s easy to overwater the plant at first. If you reach for the watering can often, choose a moderately sized, breathable clay pot with drainage holes at the bottom.

The growing medium has a huge impact on watering. Start experimenting with a new mix on an easy and familiar houseplant.

4. Utilize compost

Compost nourishes plants, enlivens the soil, and enhances the water and nutrient retention capacity of potting soil. Mature compost made from garden and kitchen waste may even suit many houseplants as is. Because compost content varies, it’s safest to mix it with potting soil. You can also add in materials that provide long-lasting aeration, such as gravel, expanded clay, or perlite.

5. Add microbes

Bokashi soil has benefits similar to compost soil, but it also contains beneficial lactic acid bacteria, yeasts, and EM microbes that contain photosynthetic bacteria. The properties of finished bokashi soil depend on the materials added to the bokashi and the soil used in the “soil factory”—the container used in bokashi’s final maturation phase. Bokashi soil typically contains nitrogen and other nutrients that plants need.

Mix prepared bokashi soil into your potting soil cautiously, about one-tenth of the total volume. A mixture that’s too strong may hinder growth and cause the leaves of potted plants to turn yellow.

soil mix houseplant bokashi soil microbial solution bagged soil — You can moisten dry bokashi soil with a microbial solution. Then you can mix it with bagged soil.

6. Sift out debris

Undecomposed plant waste in bokashi and compost soils can attract fungus gnats [in Finnish], which can especially damage the roots of small plants and seedlings. Therefore, it’s safest to sift out the debris from the soil before use.

Sifting compost soil — It’s best to sieve bokashi and compost soils before use.

7. Cover up

Compost and bokashi soils can contain bugs, just like any soil brought from outside. It’s best to place them in a container protected with insect mesh for a couple of weeks before use. Alternatively, you can dry the soil before use. Heating, however, destroys beneficial microbes in the soil and spoils its structure.

Soil mix for houseplants — Outdoor soil may contain bugs, so it’s best to put it in a container protected with mesh for a couple of weeks before use. If there are still bugs after that, let the soil dry out before using it.

First, familiarize yourself with the requirements of each plant species. Some plants are sensitive to drought, while others dislike excessive moisture.

8. Increase drainage

You can improve aeration and drainage in succulent soil with perlite, gravel, or expanded clay pellets. Species that prefer dry soil also thrive in clay granules and houseplant gravel, as long as you avoid overwatering. A breathable clay pot with a drainage hole at the bottom reduces the risk of excess moisture, regardless of the growing medium.

soil mix houseplant clay granules gravel houseplant gravel brick perlite expanded clay aggregate — On the right: orange Seramis clay granules, grit sand, houseplant gravel, and pieces of brick; on the left: white perlite and expanded clay aggregate. *Aloe plants from Plantagen, houseplant gravel from Kekkilä.*

9. Balance the moisture

Araceae plants, as well as such plants as prayer plant and calatheas, prefer fluffy soil that doesn’t get completely dry between waterings. You can mix their growing medium from various materials. Moisture levels can be balanced with materials like biochar, clay granules, houseplant gravel, moss soil, and vermiculite, as well as bokashi and compost soil. Perlite, potting gravel, coconut soil and chips, pieces of bark, and buckwheat hulls add aeration to the growing medium. Buckwheat hulls also contain nutrients.

vermiculite houseplant gravel clay granules biochar bark bokashi soil — From left to right: vermiculite, houseplant gravel, Seramis clay granules (as pot cover), biochar, bark, and bokashi soil. *Calathea, coleus, and fern from Plantagen, houseplant gravel from Kekkilä.*

10. Harness biochar

Biochar helps keep the soil appropriately moist. Coarse biochar provides aeration; fine biochar (0–4 mm) improves conditions for beneficial microbes. Regular biochar needs to be charged—soaked with a nutrient-rich solution—before use so that it doesn’t absorb nutrients from the soil. Suitable solutions for charging include EMa microbial solution, liquid drained from bokashi, poultry manure water, and urine diluted with water. Pre-activated biochar with EM microbes is also available; you should add about five percent of it to the growing medium. You can add ten per cent of regular biochar to your soil mix.