Potting soil, make your own mix!

Potting soil or a Potting Mix is vital to your plant nursery! The health of your plants is reliant on a good mix and the cost and availablity are important factors as well. Before you can start potting up plants you will need to decide on a potting soil mix.

What do you really need potting soil to do.

Potting soil is primarily a conduit to allow plant roots to receive water and nutrients. Plants take in most of their water and nutrients through their roots. If the roots dry out, the plant will die. Soil also gives the plant structure to stand up. Roots alone cannot hold a plant up. Roots are more delicate and porous than the woodier upper trunk or stems of a plant.

You don’t actually need any soil

Think of a hydroponic planting system where plants are supported in stands and the roots sit directly in water that also contains nutrients. With this in mind you really only need a potting soil or growing medium that supports the plant and can keeps roots moist with water and deliver nutrients. With this in mind you want an almost inert potting soil mix that drains, holds moisture and that you can add slow release fertilizer too. You will use a lot of potting mix so cost is a concern – keep cost in mind.

 

You can create a potting soil that works for you in your area.

Some good materials for potting soil.

• Plain old dirt – OK but often not that great.
• Course sand – drains great!
• Peat moss – Ok to keep soil from compacting but can hold too much water all by itself.
• Compost – similar to Peat Moss but can sometimes get compacted.
• Finely Ground Fir bark – An excellent medium as it holds water and still drains well
• Finely Ground Hardwood bark – Also excellent at holding some moisture and still drains well.
• Perilite – Very inert, drains well and holds moisture nicely. Great for rooting cuttings.
• Vermiculite – Similar to Perilite, great for rooting cuttings. We can buy this in large bags from some pool supply companies – it is used in pool construction.

Some materials that are really not good for growing plants in.

• Wood chips – As they decompose they can rob nitrogen from your plant. Don’t put wood chips in your potting mix unless fully decomposed. That said we do use wood chips we get for free to mulch around plants and in our plant selling area without issue.
• Clay soils – They just don’t drain and roots have a harder time clawing through dense mediums.
• Materials that are not fully decomposed like leaves or vegetative type waste. Let these fully decompose before using.

In the Southern and some North West states, finely ground pine or fir bark is readily available. Up in the North East you can generally get untreated hardwood bark that has not been dyed. Any of the barks are really good draining materials that will still hold a lot of moisture for roots. Be sure they are well ground to a fine consistency.

Sand is available inexpensively by the bag or truckload almost everywhere. We use a lot of sand in our mixes and it’s a great neutral growing medium, holds moisture. drains well, and is fairly inexpensive by the truck load. We use sand as our primary medium for rooting cuttings too.

Screened topsoil can really vary in color and exact composition. Topsoil that has a lot of sand in it can be good to use and holds moisture pretty well. We find most soils alone pack a bit too much so you need to add amendments like perilite, vermiculite, more sand or some finely ground bark.

Make potting soil in bulk quantities.

In some areas you can buy compost in large bags or by the truckload. In our area the local county operates a reclamation center where towns dump the resident’s leaves and grass clippings. They let these decompose and then screen out any large debris. We pay about $20.00 per yard for this compost by the 10 yard load. A note about compost from municipalities. Some of these are actually not as purely organic as you might think. The compost from some grass clippings and some leaves may have residual fertilizers and herbicides in them. For this reason we like to let them sit for 6 months. We turn them over and over with the bucket loader and let the rain hit them. Not really necessary but we do it anyway. Plants love this stuff either way.

Perilite and vermiculite are good growing mediums for many smaller plants. We do use them when rooting cuttings. They drain well but retain plenty of moisture. They are very expensive compared to things like bulk bark, sand, topsoil and compost.

Making your own potting soil mix.

We buy material by the truck load and move and mix the potting mix with a tractor with a loader. Thus we measure in yards but you could develop a recipe using bags or cubic feet as your measuring method. As of the moment, our potting soil mix in northwest NJ, looks something like this.

• 10 yards of compost
• 6-8 yards of course sand
• 1-2 yards of Perlite or Vermiculite.

For a total of around 18-20 yards of finished potting soil mix. The total cost is about $750.00 per batch. This will fill about 1,500-2,000 1, 3 and 5 gallon pots. So, we estimate it costs about $0.50 per pot. We never use 18-20 yards of material in just 1, 3 or 5 gallon pots so it is hard to be more exact about how many pots it will fill.

If you are working with smaller quantities of plants you might be tempted to purchase pre-made soil mixes. Avoid them especially those with fertilizers in them. These store bought mixes are expensive and some of the fertilizers can even kill your rotted cuttings or bare root plants.

Make your own mix and then add fertilizer.

Make a potting soil mix that drains well, holds some moisture and supports your plants. Assess what is available in your area. If you can get finely ground fir or pine bark at a reasonable cost that is ideal. If not a mix like ours of humus, sand, and Perilite or Vermiculite can work well for you.

What fertilizer should you use?

For nutrition we only recommend a slow release commercial fertilizer. The best two for the woody plants and trees we grow are Osmocote 14-14-14 Slow Release Fertilizer ,  3 to 4 month and Osmocote 19-5-8 Slow release fertilizer.

One of these is all the fertilizer your trees and plants will need. They are slow releasing so generally an early spring and early fall application is more than sufficient. Most importantly, they won’t burn your plants. Plants need nutrients over time, not a blast.

What else can go in Potting Soil mixes?

We have about covered the practical options but we have started some alternate ingredients. Tucked away is a large compost pile. We have gotten several loads of wood chips dropped off for free and will let them decompose for 3 to 5 years. It is also possible to find landscaper who wants a place to drop grass clippings and leaves. If you have the time and space it might make sense to start stock piling some of these materials. Let them decompose and mix them in.

That is all our advice on potting soils and mixes other than to say please do experiment. We keep tweaking our soil mix but it’s mostly out of curiosity. We have not done a lot with fir, pine or hardwood bark but it’s on our list to try.