What is potting mix?
Potting mix is an essential ingredient for both indoor and outdoor plants grown in containers. A soilless (i.e. no sand or clay) mixture is typically used, made from peat moss, wood chips or bark and minerals like perlite or vermiculite, in addition to compost. This mixture is used because houseplants need to be planted in the right conditions that allow good air circulation so their roots can grow. Peat moss is often the main ingredient in the potting mix due to its ability to retain water and hold nutrients.
- Good drainage and aeration.
- Made from sterile ingredients (some sources say the mix has been treated to ensure no diseases/insects/weeds are present).
The problem with peat moss
Peat moss is a problematic product, as it’s an organic resource that regenerates very slowly. When used as a growing medium, it decomposes after about 2 years.
Peat moss comes from peat bog wetlands which are a very important ecosystem. Not only are they habitats for a variety of wildlife they act as carbon sinks and have been storing carbon for thousands of years. So they have a vital role to play in tackling climate change.
However, due to demand from the agricultural and horticulture industries, this precious resource is being exploited at an unsustainable rate. In Europe, peat extraction is strictly regulated because of the negative impacts of overharvesting.
Can you reuse potting mix?
Short answer: Yes, you can, at least for some time! As most of the potting mix you buy in stores has peat moss, the sustainable thing to do would be to reuse it. But peat moss is the only ingredient that expires, it has a shelf life of about 2 years. As peat decomposes quickly eventually it won’t offer adequate drainage for your plants and there’s a risk they’ll become waterlogged.
Luckily, you can give your potting mix a longer life, by adjusting the ingredients. According to some sources, coconut coir can be reused 2-3 times longer than peat moss.
And don't forget. The first thing to do when reusing or refreshing the old mix is to check if there are any pests or plant debris and remove it.
Coconut coir has been getting attention as a sustainable eco-friendly alternative to peat moss. Coconut coir is a by-product of coconut production and using it in potting mix utilises what would otherwise end up as waste. Like peat moss, coconut coir acts as a soil conditioner and has many of the same functions in the potting mix.
An added benefit is that coconut coir is hydroponic and retains more water than peat moss, great for plants that love a moist environment!
Coconut coir as a potting medium is low in nutrients so it's important to add some from the beginning.
Nutrients and microbiome
So we’ve said that potting mix is sterilized to keep the bad stuff like pests away from your plants. But did you know that your plants actually need a healthy micro life in the soil to thrive? So adding some life to reused, or even new, potting mix is often a good idea.
Microbes are major players in decomposition and nutrient cycling. They’re important for your plant's health because as they move through the soil they aerate it and help improve soil drainage and structure.
You need to pay attention to the microbes, now!
Microbes are key to having a balanced ecosystem that lets your plants not just survive but thrive! They can:
- Fight off harmful bacteria and fungi
- Improve immunity to disease and pests
- Add nutrients to the soil and improve nutrient absorption.
How to add nutrients while also encourage a healthy micro life?
- Add compost, microbes need lots of organic matter to thrive.
- Microbes do well in moist soil so make sure soil is well-watered.
- Avoid using chemical pesticides.
- Use organic fertilizers based on compost or manure.
- An alternative to store bought fertilizer is using old coffee grounds mixed with water to nourish your plants. Coffee grounds are a slow-release fertilizer and are full of essential nutrients such as phosphorus, potassium, magnesium, and copper.