It sounds like you are asking about the ingredients for the soil potting mix you are using in containers. Vermiculite has a number of advantages other than just for drainage but I understand you are looking for a more economical alternative. There are other substitutes such as coarse washed river sand that provides excellent drainage properties and can be obtained from landscape suppliers very economically. Just take a bucket or container with a lid to avoid it spilling on the way home. They will weigh it for you and it is a cheap option.

If you want to work out what percentage to mix into your compost, I’ve written an article on the role of different ingredients and a recipe with suggested quantities in a DIY potting soil mix which may be helpful to you to consider alternatives you could try.

My personal research into polystyrene has led me to believe that when it is in a moulded form such as the food grade boxes used by grocers, the styrene (which some studies have indicated can leach harmful chemicals) is stable. When the boxes break up or are damaged the polystyrene structure is compromised. I use the boxes to grow in but only if they are in good condition. I won’t use the beads as I don’t want to risk contamination of my soil and food crops and there are a number of health concerns. In a typical MSDS (Material Safety Data Sheet) on the beads, it advises:

• Avoid prolonged or repeated breathing of gases, vapors, or mists.
• Avoid prolonged or repeated contact with skin.
• Use with adequate ventilation.

This would require you to use gloves and a protective face mask whereas if you use a natural alternative such as coarse washed river sand (to remove the salt), then there’s no need.

The impact on the environment is another consideration. The article ‘Dangers of Styrofoam Beads’ says:

“Styrofoam beads pose a threat to the environment as they are not easily recyclable. To break them down, they must be melted using special equipment. Since burning Styrofoam beads can release toxic gases into the air, they can damage the environment even when they are being recycled.”

I personally believe there are much safer alternatives where you are not putting your soil, the environment or food at risk. I’d rather err on the side of caution! I feel the same goes for the types of containers we choose to grow our food in i.e. what they are made from (See ‘Safe Containers for Growing Food’).

This is just my take on it – I’m sure others have their own views! Hope this helps.

Glad this was of some use. I try to do my ‘due diligence’ as much as possible into materials I use or bring into my garden, especially for growing food. This way I can control or minimise contamination from unnecessary chemicals and toxic substances – not being paranoid, just a more conscious consumer I guess! It’s kinder to the environment and creatures that live here too.

I’ve also found when thinking about whether to use a product, I find out whether it is natural or not to help me make a better choice. Vermiculite for example is a natural occurring mineral whereas polystyrene beads are a synthetic manufactured product. Happy gardening.