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Why You May Not Want to Reuse Pro-Mix

August 30, 2019

  • Reusing Potting Soil
  • Issues with Reusing Pro-mix
  • Different Types of Pro-mix

Small One Gallon Pot Pro-mix

Image of a cannabis plant being transplanted from a 1 gallon pot. The plant is rootbound, but healthy nonetheless. Grown by RMK.

Reusing Potting Soil

It is possible to reuse potting soil for many residential vegetable gardens or adding to compost piles, but there are some issues with reusing potting soil that are similar to issues with reusing Pro-mix. Issues with plant pathogens, pests, and minerals in the substrate can hinder the plant’s growth or potentially kill it. When taking certain precautions it is possible to reuse potting soil in certain circumstances for cultivation other than cannabis. People commonly reuse potting soil at home for their vegetable gardens or flower beds. Pasteurization or exposing the soil to heat for several days can eliminate plant pathogens from the soil and re-introducing certain minerals back into the substrate can be a possible solution to these issues if done properly. Knowing the issues and possibilities to correct deficiencies in potting soil can help us better understand the risks of reusing Pro-mix for cannabis production.

Transplanting with Pro-mix

Image of a cannabis plant sitting in a big tub of Pro-mix. The plant is more than ready to be transplanted into a larger pot! Grown by RMK.

Issues with Reusing Pro-mix

Pro-mix is a popular peat moss based substrate that is popular with both residential and commercial cannabis growers. There are similar risks between reusing potting soil and reusing Pro-mix, but they are not the same. One of the issues of trying to reuse Pro-mix is that the limestone used to raise and regulate the substrate’s pH will have broken down over time which will cause the substrate to become more acidic. This can be resolved by adding in more limestone to the used Pro-mix (1). Another issue for trying to reuse Pro-mix is that the wetting agent added to the mix will have also broken down and a wetting agent will have to be re-applied before reuse. The issues of limestone and the wetting agent can be easily resolved but any potential plant pathogens or plant pests that live within the substrate could potentially affect the next plant (2). If you are experiencing any sort of issue with plant pathogens or pests than it may be wise to just toss the Pro-mix instead of trying to reuse it as the cost of purchasing the Pro-mix is relatively cheap. Leaving the substrate out in the sun to pasteurize is not enough to kill all plant pathogens or pests living in the substrate and is a risk taken that could cause more harm to your cannabis grow. .

Cannabis Plant in Large Pot of Pro-mix

Image of a cannabis plant after transplant into a larger pot. The plant is now prepared to grow full size. Grown by RMK.

Different Types of Pro-mix

There are many different Pro-mix substrate products that are used in cannabis production. Depending on which Pro-mix product you use, the additional ingredients will have to be added in if you attempt to reuse Pro-mix. There are lots of Pro-mix products in existence which makes the use of mycorrhizal inoculants to increase the health of plants. If you want the added benefit from mycorrhizal inoculants when you reuse Pro-mix, then it will have to be re-introduced into the substrate.

  • Pro-mix BX - General Purpose
  • Pro-mix HP - High Porosity
  • Pro-mix MP - Multi-Purpose
  • Pro-mix HPCC - High Porosity Coir-Based
  • Pro-mix BX Bio-Fungicide
  • Pro-mix BX Bio-Stimulant
  • Pro-mix MP Organik

Pro-mix Products

There is a large selection of Pro-mix products offered on their website.


  1. Vossen, Paul. (n.d.). “Changing pH in Soil”. University of California Cooperative Extension.

  2. Beuchel, Troy. (2018). “Pro-mix Grower Services Q&A Video: Can I Reuse Pro-Mix?. YouTube Video.

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