Soil mixes for plant propagation and germinating seeds

For propagation of your plants and for seed germination indoors or in a greenhouse you will need different types of soil. Some seeds are sensitive to the type of soil and the diseases related to the ground and this means that they can best germinate in a soilless substrate. In addition, most of the cuttings prefer a soil-less substrate. Nevertheless, there are seeds that require immediately nutrients and then they are the best seeded in a rich soil mixture. On this blog we will make often references to these particularities.

Ingredients for your soil mixes will be shown below.

Leaf mold

It is obtained from rotting leaves and it has a high cationic exchange capacity, good mineral content but it is missing macronutrients (Nitrogen, Phosphorus and Potassium). It has a lower pH and may contain agents for diseases. It should always be sterilized. Coarse texture is best used in rooting media or potting mixes.

Well rotten compost

Compost

Compost results after the decaying organic material under the influence of fungi and bacteria. Because of the existence of microorganism it may protect your plants against diseases. It has a high cationic exchange capacity and a good balance between macronutrients and minerals.

Fine washed river sand

Fine sand

It is used for a better drainage of your soil because the sand grains have different sizes and the water is drained quicker leaving air spaces in between. It is inert and it does not contain any nutrients. Use always washed sand and never use sand from the beach because it contains killing amounts of salt.

Grit

Grit or coarse sand

Use always washed grit or coarse sand to improve drastically the aeration and drainage of your mixes. It mostly used for the rooting of cacti and other desert plants that require a more open medium.

A brick of dehydrated cocopeat

Coconut fibres / coco peat

Usually are sold in forms of dehydrated bricks that need to be rehydrated before use. It is derived from composted coconut shells and it is good replacement for less fine sphagnum moss in soilless substrates.

Perlite

Perlite

It is resulted from expanded volcanic rocks. It retains the water good and because it is inert it also drains water quickly. It is used in sterile mixes to improve drainage and aeration.

Potting soil

Potting soil

Use soil of the best quality for seed germination and plant propagation. The soil must free of any other seeds, insects eggs. This soil is used for rich soil mixes.


Coir

Coir is a fibre resulted from coconut husks used as peat substitute. It dries out less quickly that peat but
requires more feeding. It is a good base for soilless mixes.

Peat

Peat

Is stable, long lasting and well aerated and retains the water well, but low in nutrients. It is difficult to re-humidify once it has gone dry. It is used for lightweight mixes intended for short use.

Dried and groud moss

Sphagnum moss

Sphagnum moss

Do not use coarse sphagnum moss in propagation for this is intended mostly as an orchid medium. Use finely ground sphagnum moss for soil mixes intended for seed germination and semi-coarse for cuttings media.

Vermiculite (magnified photo)

Vermiculite

It is expanded and air-blown mica. It contains traces of Magnesium and has high cationic exchange capacity. Acts similarly as perlite but holds more water and less air. It supports drainage and aeration. It comes in various degress of grinding. Some of the finest are used on the top part of the substrate as a physical barrier against harmful bacteria and fungi.


 
Fine bark

Fine bark or chipped barked is used as peat substitute or for free draining acidic mixtures, especially for orchids, palms and other indoor plants.

Recipes for mixes

Making your own mix has the advantage of knowing what your mix contains. Accordingly, you can realize the ideal medium for a specific type of propagation technique or plant. You can find in the shops ready-made soil mixes generically Seeding and Cutting Soil Mix. When you mix your substrate, hygiene is very important. Use only clean tools and sterilized soil.

How to sterilize soil?

If you are planning to use garden soil in your mixes it is crucial that you sterilize it before incorporating it. Sterilization will kill possible harmful organisms that could affect seedling and cuttings. To do this the soil must sifted to remove clumps, stones and any other residue, but also to obtain a finer structure. Sterilizing garden soil for commercial use is done in special units. These are expensive and unnecessary for home use. An oven or a microwave would do just fine.

For soil sterilization in an oven you will need a deep baking tray, of about 8 to 10 cm. Bake the soil for about 30 minutes on 200 degrees C. You should know that unpleasant badly-smelling vapours may be released.

In order to sterilize soil in the microwave you need a roasted bag, resistant to high temperatures. After soil is inserted seal the top of the bag to avoid the contamination of the microwave. However, make a few holes and place in the oven for 10 minutes on maximum power.

Observation: some of the substrate mixes cited below, require some addition of non-biological nutrients. You may avoid using those mineral nutrients by excluding them from the mixes. Later on we will publish some ways in which you can obtain your own biological fertilizers.

Substrate recipes for potting mixes, rooting media and seeding mixes.

Rich potting mix	Soilless potting mix	Soil based seeding mix
2 parts compost 1 part potting soil 1 part sand 1 part vermiculite 1 part perlite	3 parts peat or substitute 1 part sand or perlite For each 36 liters add 14 g ammonium nitrate 28 g potassium nitrate 45 g superphosfate 85 g ground limestone 85 g dolomitic limestone	2 parts potting soil 1 part peat or substitute 1 part sand
7 parts potting soil 3 parts peat or substitute 2 parts sand For every 36 litres add 113g general purpose slow release fertilizer and 21 g limestone	3 parts peat or substitute 1 part sand or perlite For each 36 liters add 14 g ammonium nitrate 28 g potassium nitrate 45 g superphosfate By avoiding the use of limestone you will obtain an acidic composition	2 parts potting soil 1 part peat or substitute 1 part sand For each 36 litres you may also add 42g superphosfate 21 g ground limestone
7 parts acidic potting soil 3 parts peat or substitute 2 parts sand For every 36 litres add 113g general purpose slow release fertilizer This potting mix is used for acidophile plants.		2 parts potting soil 1 part peat or substitute 1 part sand For each 36 litres you may also add 42g superphosfate

Soilless seeding mix	Soilless rooting media	Sterile substrate
3 parts peat or substitute 1 part fine bark 1 part perlite For each 36 litres add 36 g trams of slow release fertilizer	1 part peat or substitute 1 part sand (or perlite or vermiculite)	1 part finely ground Sphagnum Moss 1 part perlite
1 part perlite 1 part vermiculite 2 parts finely ground sphagnum moss	1 part peat 1 part fine bark To each 36 litres add 36 g of slow release fertilizer	1 part cocopeat 1 part perlite
	1 part peat 1 part fine bark 1 part perlite To each 36 litres add 36 g of slow release fertilizer