Make and sterilize your own potting soil and seed soil

When growing young plants, the substrate takes on specific tasks that have long since been fulfilled when potting soil comes into play. If seeds are planted in the ground, the hobby gardener will encourage them to germinate with targeted care under suitable site conditions. The cotyledons appear and growth begins. In order for the very delicate roots to develop optimally, a certain level of motivation is therefore required, which is no longer required in established plants in this form. While with potting soil the nutrient supply is in the foreground, with potting soil the focus is on the following aspects:

• Low in nutrients, without mineral salts
• Loose, rich in microorganisms
• Fresh, not too dry, not too wet
• Well drained and still capable of storing water

These expectations of the seed soil signal at first glance that potting soil cannot meet them. Even the fertilizer contained in it would significantly impede any attempt at cultivation, if not destroy it altogether. The mineral salts are far too hot for fine seedling roots. In addition, the young plants would hardly bother developing their root system, with a mountain of nutrients just before each root tip.

Classic mix based on peat

A simple mixture that always fits uses peat as the central component.

• 3 parts peat
• 2 parts quartz sand
• 1 part algae lime

Due to its airy consistency, peat is considered the ideal medium for seed compost. Peat is able to store up to 75 percent of its own weight in the form of water. At the same time, the material is low in nutrients and acidic, giving hobby gardeners plenty of scope to add other ingredients.

Potting soil without peat

Decades of overexploitation of moors means that in a few years there will be no more peat in nature. As a result, environmentally conscious hobby gardeners are reorienting themselves and opting for peat-free seed soil. A singular peat equivalent has not yet been discovered. Rather, a combination of natural fillers and garden soil has proven itself.

Compost
Green waste, garden waste, kitchen leftovers and other organic waste are transformed into rich humus by industrious earthworms and microorganisms. The result is a valuable peat substitute and soil conditioner that also contains nitrogen, potassium, phosphorus and magnesium.

Bark humus
If pine and spruce bark is composted over a period of years, it becomes a sought-after material for high-quality seed compost. Bark humus has a stabilizing effect on the structure of any substrate without impeding permeability. In addition, a lot of useful microorganisms cavort here.

Coconut fibers
The shells of coconuts are processed into fibers and result in an airy, light base material for high-quality potting soil. Poor in nutrients, in combination with other peat substitutes they prevent an undesirable accumulation of nitrogen & Co. Coconut fibers thus make a significant contribution to the indispensable loosening of any substrate. Specialist shops offer the material in handy blocks that are dissolved in water and expand by six times their volume.

Wood Fiber
Similar to wood chips, wood fiber is the refined version of it. Like coir, they contribute to the airy consistency of seed compost while decomposing more quickly. In addition, the material scores with a low pH value and minimal nutrients. When buying wood fibers, you should make sure that it comes exclusively from untreated sawn wood.

Sand
A good seed compost cannot do without sand as a mineral additive. It contains no nutrients, does not rot, prevents waterlogging, gives the substrate structure and the pot stability.

It is not absolutely necessary to add all the components presented to a potting soil. Of course, the type of plant that is used has an influence on the composition. For example, if it is a heavy feeder for the kitchen garden, such as peppers or Brussels sprouts, a small proportion of compost should provide nutrients. For the sowing of cress or other weak feeders, you will want to do without nutrients.

Mix the potting soil yourself

Potting soil for heavy feeders

• Compost (30%)
• garden soil (10%)
• Wood or coconut fibers (40%)
• Beef hummus (10%)
• Sand (10 %)

Potting soil for medium eaters

• Compost (20%)
• Beef hummus (10%)
• Wood or coconut fibers (55%)
• Sand (15 %)

Cultivation soil for weak consumers

• Beef hummus (5%)
• Wood fibers (40%)
• Coconut fiber (40%)
• Sand (15 %)

Optionally, a little algae lime, rock flour or charcoal ash can be added to all mixtures as a prophylactic against fungal infestation.

Fertilize the pricking soil a little

In the cultivation of the vast majority of all plants, isolation represents a stage between sowing and final transplanting into beds or tubs. While the fine structure of the soil should be maintained so that the roots of the seedlings, which are still very delicate, can grow well, various nutrients can now be added. Horn shavings and horn meal have proven to be important nitrogen suppliers for this requirement because they can be easily dosed. Thoroughly sifted compost is also a good idea. Otherwise, nothing changes for the production of pricking soil compared to the seed soil used up to then.

Special mixtures for exotic plants

Those who devote themselves to the cultivation of unusual plants from foreign parts of the world in their hobby gardening are usually not satisfied with potting soil for native plants. The more detailed the substrate mixture meets the exotic demands of foreign plants, the greater the chances of success for the cultivation. The following examples provide an initial overview:

The carnivores

Carnivorous plants, such as the Venus flytrap , do not take nutrients from their substrate. They only use live prey to feed themselves.

• White peat (70 to 80%)
• Quartz sand (5 to 10%)
• Perlite (5 to 10%)
• Sphagnum (5 to 10%)

Seed soil for carnivores must not contain the slightest amount of humus or nutrients. In addition, sterility is of essential importance.

cacti

For the cultivation of extremely weakly consuming cacti, there is a very inexpensive variant for the substrate that cat owners already have in the house.

• Mineral-based cat litter
• Perlite
• Bimskies

The special ability to store water qualifies cat litter (not clumping litter) for use as seed soil. It can be used as a sole substrate or mixed with perlite or pumice. The absence of any nutrients is important, because otherwise the undemanding roots of a cactus will not even start looking for food.

orchids

Those who have mastered the art of eliciting ripe seeds from their orchids will undoubtedly not confront them with commercially available seed soil. The decision to use self-made substrate should pay off, especially for the cultivation of the popular epiphytes. Two components stand out here. Pine bark is extremely low in nutrients and provides the roots of the seedlings with support right from the start. In addition, the natural material can easily be enriched with fertilizers later in the course of cultivation. Sphagnum, the popular peat moss, takes up a lot of space in the care of orchids and has proven itself in the cultivation. Both materials complement each other very well for the cultivation of most types of orchids. By adding a little bit of charcoal ash, you effectively prevent a fungal infection.

Protea – sugar bushes

Hobby gardeners who take up the challenge of a Protea will not want to leave anything to chance when choosing suitable growing soil. The silver tree plants native to South Africa are undoubtedly on the same level of difficulty in cultivation as orchids. Experienced hobby gardeners who produce seed soil themselves advocate the use of vermiculite, a clay mineral that is combined with lava granules and a touch of nutrients.

• Vermiculite (40 bis 50%)
• Bark humus (20 to 30%)
• Lava Granules (20% to 30%)

Sterilize without much effort

Homemade potting soil should definitely be sterilized before use to rule out contamination by fungal spores, insect eggs or viruses. This also applies to ready-made substrate. No cumbersome effort is required for this purpose, because the necessary equipment is already in your kitchen in the form of the oven, microwave or pressure cooker.

• Fill a fireproof form with potting soil
• Place the lid loosely over it
• In the oven at 180 degrees Celsius for 30 minutes
• Alternatively, put it in the microwave for 10 minutes at 800 watts
• Steam in the pressure cooker for approx. 60 minutes

After the soil has cooled down, it should be used immediately for sowing. Otherwise, it is advisable to keep them airtight so that insects or spores can still sneak in.

If you are faced with the task of processing a larger quantity of potting soil, a simple test will provide you with information as to whether sterilization is necessary at all. They take a sample from the substrate and sow cress on it. In healthy seed soil, the cress germinates within 3 days and develops white, healthy roots in a week. If this is not the case, you cannot avoid sterilization in the oven or microwave.

Conclusion
Only potting soil of the best quality offers seeds and seedlings a good start in life. Instead of accepting the unpredictability of commercially available products, experienced hobby gardeners produce their own seed soil. Even a simple peat-sand mixture with a little algae lime delivers good results. Environmentally conscious hobby gardeners avoid using peat in favor of renewable fillers and upgrade the seed soil with a small dose of nutrients if necessary. At the same time, this method offers plenty of scope to develop an individual house mixture, tailored to the needs of the cultivated plant species. Anyone who does not miss the final sterilization in the oven or microwave will be rewarded with self-made growing soil of premium quality.