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Soilless Potting Mix For Healthier Seedlings


Photo of Soilless Potting Mix Simple homemade soilless potting mix

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Soilless Potting Mix

While not often recognized there is a difference between a soil less potting mix and a sterile soil less potting mix. Not all soil less potting mix ingredients are sterile, in fact there are very few amendments that qualify. If your aim is to provide a safe environment for seed raising then the type of potting mix you use is important.

The traditional soilless potting medium was designed as a sterile growing medium, usually sphagnum peat or more recently coconut coir fiber, and is used instead of soil or other similar products, as a soil substitute for growing plants in any contained environment. The purpose of a soilless potting mix is to give more control over soil-borne diseases, contaminates and many other problems that plagues potting mixes containing other materials.

Soil or garden loam comes with a range of problems and are the main reason why over fifty years ago these potting mediums were developed. Young plants, especially seeds and young seedling, that are confined in seed cells and pots are particularly vulnerable to many of these problems.

None Sterile Material

The boundaries between a soilless mix and a sterile soilless mix are commonly crossed without any thought to what is being done. Many potting mix ingredients, even some of the better ones, are considered soilless but they are not always sterile.

Photo of potting mix ingredients

Photo left - Exploring alternative methods and materials is part of the enjoyment of gardening and different potting mix recipes is no exception. When using soil less potting mix ingredients that are not sterile it should be remembered that the problems gardeners had using growing mediums, like compost, soil, wood products, leaf mould and similar ingredients, before the advent of the soilless potting mix will be no less a problem today. There is always an element of risk, when adding these ingredients to a potting mix and they will need to be treated differently to the traditional sterile soilless ingredients. Follow this link for more on what’s what with potting mix ingredients
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For those new to seed raising the safer approach is to use traditional sterile soilless potting medium or at least use them for a portion of the seedlings being raised while experimenting with alternative ingredients. With the proper care either method will produce the desired results.


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Pre made Pellets

You cant talk about soilless mixes without including some of the many pre made seed starting pellets and blocks.

Peat Pellet

Photo of using peat-pellets
Photo of soilless potting mix using peat-pellet

Photo Left One - Growing seedlings using sphagnum peat pellets are an excellent way for a novice or someone with limited time and space to raise their own seedlings.
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Photo Left Two - Young Radicchio seedlings - These pre-made compressed seed starting pellets are independently wrapped to retain the soil making them easily moved around without disturbing the seedling.
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Bio Sponge

A bio sponge is plug of sterile medium with a hole in top made for germinating one seed, there are a number of different sizes


Photo of  soilless potting mix starting seeds using bio-sponge

Photo Right - They are excellent for maintaining aeration and water retention, and as seen here allow the roots to freely penetrate the sponge.
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Coconut Coir Pellets

Growing seedlings using coconut coir fiber pellets is similar to using sphagnum peat pellets. Simply add water, watch them swell, and sow your seed.

Photo of soilless potting mix using coconut coir premade pellets

Photo left - Coir pellets are held together with either bio-degradable netting or some with paper wrap which will not fall apart but still allow the roots to penetrate the sides.
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Buying A Soilless Potting Mix

It is not a simple job buying a soilless potting mix. It can be confusing picking out a bag of soilless potting mix from the many different types and labeling used. Unfortunately very few potting mix labels will contain the words “soilless” or even “soil less”.

The best a gardener can do when looking for the product they want is to properly read and assess the label or list of contents. Knowing what each ingredient in a potting medium is and how it acts and affect the potting mix is helpful. For more details on many of the ingredients common to potting mixes follow this link potting mix ingredients.


When looking for a potting medium for starting seeds, ensure the packaging stipulates for starting or germinating seed.




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More Information







Coconut coir fiber is one of the few amendments that can be used as a total replacement for the peat component in soilless potting mixes.
Pricking out seedlings, or thinning out, is the term used for the first potting or transplanting of young seedling that are grown in seed trays, flats or any container that the seeds aren’t individually planted. Pricking Out Seedlings
Wetting agents are include in most commercial potting mixes to help regulate moisture, improve aeration, and increase nutrient availability. Wetting agents are not essential for successful seed raising and most do not qualify for organic certifying. If this is of concern to you then when looking to purchase a potting mix look for one that is organic certified.






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