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Perlite and Vermiculite for Seed Sowing

Perlite and Vermiculite are both minerals found in nature

Both horticultural grade perlite and exfoliated vermiculite are used in gardening, especially seed sowing

Both are light, inert, non-organic (not derived from a living organism) substances that are good for maintaining aeration in the soil by maintaining space between the soil particles. However they function differently in terms of their effect on water retention in the soil.

What is Perlite ?

Perlite is mined in regions that have seen ancient volcanic activity. It is really a form of volcanic glass. The material is formed under great heat within volcanoes so that it expands a bit like exploding popcorn. Steam from within the rock forms a structure of tiny bubbles which harden as the ash is pushed from the heat then cools.

Perlite is whitish in colour and appears crumb like because of the bubbly structure inside. It feels hard but will crumble if enough force is applied between the fingers.

perlite-granules

There are various accounts of success and failure using perlite in a seed compost for specific plants.

Perlite does cause algae to grow, owing to the water that is held on the surface, this can become a concern as it does not look very nice if you have a green carpet of algae on the top of the seed compost (normally you will only get this after a long period of time) but it has not been proved to do any real harm.

For a range of seed sowing perlite products click here

 

What is Vermiculite ?

Vermiculite is a silicon mica-like material, mined from the surface of the earth. It is formed of thin layers of silicon compounds. When heated, the layers separate (exfoliate) within the vermiculite. The spaces between the layers can hold considerable quantities of water which are bound into the space by water surface tension.

Vermiculite is biege/light brown in colour and has a soft texture flaky feel to it.

Image by: Jungle GardenHorticultural grade exfoliated vermiculite is the best choice for seed production. When added to soil, it holds moisture and reduces the need for watering.

Image by: hddod

Image by: hddod

Vermiculite can also be used as a seed covering material, as can be seen here on the left, especially if the seeds require light to germinate. Instead of using sieved compost to cover the seeds use a light covering of the horticultural vermiculite (fine grade). Excellent seed germination results have been achieved using this method for covering seeds.

To make a soil-free growing medium for seeds, combine vermiculite with peat (or alternative) or composted pine bark. This mixtures retains air, nutrients and moisture. Very little watering is required.

Some have even used vermiculite alone, if this is your chosen method then you should feed the seedling with diluted fertilizer when the first true leaves begin to appear.

For a selection of seed sowing vermiculite products

 


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