How to Make a Potting Mix
Making your own potting mix can save you a lot of time and money. Not to mention you will be able to provide your plants with a god mixture ideal for their needs. Also, making your own potting mix ensures quality ingredients – you always know what is in the mix you intend to use.
The first thing you need to know is that there is not a single potting mix recipe ideal for all plants. There are different types of mixes and certain plants have unique demands. However, if you wish to make a basic potting mix you can use for most of your gardening needs, it’s important to keep it simple. This approach will also help you learn the basics and understand how a good potting mix is made. Once you become more experienced you can start experimenting with different ingredients and potting mix types.
Tools and Materials
Here is the basic list of tools needed for making your own potting mix:
- A container for measuring.
- A bucket (preferably large) for mixing.
- Easy access to water (hose, watering can, etc.)
- A small fork and trowel.
- A sieve.
- Additional container (for pre-soaking).
- pH meter.
- A pair of gardening gloves.
- A mask (not necessary, but it will prevent you to inhale dust or organic particles).
When it comes to ingredients, here are the most essential ones:
- 1 part Coir Peat (pre-soaked). It’s cheap but it’s a great, renewable resource you can use. It’s also a good environmental choice (it’s a waste by-product from coconut-processing industry). There are some products of husk fibre processing you want to use, and they are called coconut coir or coir peat. They should not be confused with peat moss. Coir peat comes in lightweight compact blocks you can get in various sizes. It’s easy to find them in most garden centers but also try supermarkets, produce and hardware stores. Coir peat is good because it provides aeration and water holding capacity. Also, it adds bulk to the mix.
- 1 part Vermiculite. A good size is grade 3. You’ve probably already seen vermiculite: it’s that silvery-grey color you often see in potting mixes. Vermiculite is natural volcanic mineral that has been expanded with heat in order to increase its water holding capacity. Vermiculite’s particles will soak up moisture and nutrients, thus keeping them in the mix so plants can access them. Vermiculite is lightweight and inorganic so it will not lose volume in the mix. It’s also sterile, clean, odorless and non-toxic. Another advantage is that it can’t become mouldy or rot. It has a moderate cation exchange capacity (CEC) so it can easily hold minerals and make them available to the plants. Depending on the brand, the pH may be a little alkaline.
- 2 parts sieved Compost. It’s always best to use homemade compost but you may also use a commercial certified organic mix if you don’t have homemade compost. To sieve your compost, it’s best to use a metal sieve attached inside the lip of a bucket. It makes it easy to remove any lumpy bits and everything is sieved directly into the bucket. Compost is good because it provides moisture, retains minerals and gives plant food. It also keeps good microbes and it improves the structure of the growing media. Compost can act as a buffer to changes in pH. It can also help suppressing diseases.
- 1/2 to 1 cup of Worm Castings or Vermicast (humus). Again, it’s best to use homemade worm castings (you can have your own worm farm) and homemade humus. However, if you don’t have homemade worm castings and humus you may use commercial ones. Humus offers numerous benefits, such as the capacity to hold nutrients and transfer them to your plants. It also has a great moisture retention capacity (it can hold about 80%-90% of its weight in water) and it provides beneficial microbes. In addition to this, it’s a plant food source and a buffer for toxic metals and chemicals. It also has the optimum soil crumb texture. The quantity listed here will be good for making about 36 litres (4×9 litre buckets) of potting mix, with a 9 litre brick of coir peat.
One important note: a “part” can be any quantity you need; it’s their ratio that matters. You can use a small scoop or icecream tub to make one part, or a 9 litre bucket or even a wheelbarrow, depending on how much potting mix you need. Usually, people make one large bucked of potting mix but it’s not a rule: you can make more or less than this. Remember, if you make more than you need at the moment you can always store it until you need it again.
Making the Mix
Now that you have all the tools and ingredients, it’s time to make your potting mix.
Step 1: Pre-soak coir peat in warm water. It’s best to use a large plastic container. Rehydrating a 9l block requires at least 4.5l of water, so you need a bucket bigger than 9l to work with. Use a larger bucket, at least 14l in size. When you see coir peat rehydrated, loosen and fluff it with your trowel.
Step 2: Mix equal quantities of pre-soaked coir peat and vermiculite (or sand, if you use it). Use a large separate container for that. First, blend the coir peat and vermiculate together before adding more ingredients. This will help you get an even mix.
Step 3: Add the sieved compost and worm castings to the mix. Blend all the ingredients together like you’re making a cake. If you have some optional nutrients and additional ingredients (see below), this is a good time to add them to the mix. When mixing, you may need to moisten lightly with a watering can. Moisten it until you can squeeze a few drops of moisture out of the mix or until the mix has a nice moist but it doesn’t feel fully wet.
Step 4: Check the pH with a meter. You can get a handy pH testing tool for around $10 at a hardware store. For most plants, you will need pH values to be between 6.0 and 7.0. However, if you want to grow vegetables, you need to keep it precisely between 6.2 and 6.8 pH. On the other hand, some plants require a more acidic mix (such as azaleas, gardenias, rhododendrons and blueberries)
Step 5: Store your mix in a container. Make sure that the container has a lid to avoid drying the mix out. The only exception is if you want to use the whole potting mix straight away.
This is all you need to make a basic potting mix you can use for your plants.
As explained in the step 3, you may also add more nutrients. This is an optional step but it can greatly improve the quality of your homemade potting mix.
You may wish to add nutrients to the pot after you have added the plant. However, opening numerous packets and containers each time is time consuming and very repetitive. Chances are that you have a limited time in the garden. This is why it’s best to add nutrients directly to the potting mix while you’re making it.
You can add both minerals and slow release organic fertilizer. Blend them easily with the mix all at once. Later, when you wish to plant your plants, all you need to do is to place them in the potting mix and add water: your potting mix will come with everything you need to start growing.
What can you add? Here are just some of suggested minerals and other nutrients:
Rock minerals. These are essential. Add about 1 cup of a balanced dry mineral mix. You may also use crushed dust. They will last a long time in the soil and release nutrients to your plants gradually.
Slow Release Fertilisers and Soil Conditioners. Use quality fertilizers and soil conditioners to improve your potting mix. They will provide great results and improve the quality of your mix.
Seaweed & Fish. These nutrients will enrich the mix with important trace elements made for boosting root growth, disease resistance and plant health. They will also transplant shock and provide many other benefits. Add a “strong” quantity of seaweed and fish emulsion to the hot water when rehydrating the coir peat block. It will be absorbed into the coir peat.
- One note of warning: you need to keep it safe. Always wear your gardening gloves, and it’s advisable to also use a mask. You don’t want to inhale any dust or organic particles and you sure don’t want to risk any disease. Make sure to wash your hands afterwards. Don’t make your mix on a windy day. To increase safety, you may also consider safety glasses and a spray bottle (to mist water over the dusty ingredients).
- If vermiculite is unavailable, you can use coarse river sand.
- When pre-watering coir peat, it’s best to use hot water. It will speed up hydration.
- To raise the pH of your potting mix by about one unit to make it more alkaline, add about 1 to 1.5 grams of dolomite (lime) per one litre of mix. To lower the pH by about one unit (to make it more acidic), add 0.3 grams of sulphur per litre of potting mix. Make sure to keep the mix moist and recheck the pH levels after a few days.
- Remember, plants need some good balance of minerals and other nutrients for health and reproduction. This is why it’s beneficial to include additional nutrients to the mix, even though it’s an optional step.