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The Do’s and Don’ts of Reusing Grow Media

The Do’s and Don’ts of Reusing Grow Media

Hydroponics is all about minimal inputs for maximum results. Most of the time we think about electricity and water, but there are other inputs that can be streamlined, including our growing media. If you read our previous blog post, you know the difference between soil and growing media, but they have something in common: they can be recycled and used over and over in your garden, indoors or out.

Potting Soil

Water draining from pipe

First things first, be aware that excess nutrients left over from your previous crops will be left in the soil. Flushing these out is very important in order to a) not burn your crop with excess salts and b) know how much nutrient to add later. Flushing with a nutrient flush like BushDoctor Sledgehammer from Fox Farm or Royal Flush from Humboldt Nutrients will rinse out excess salts and heavy elements leaving cleaner soil. Even if you already flushed your soil in the final stages of your grow cycle, do it again. And maybe once more….just to be safe.

Next, give your soil a rest period. This means, allowing it to totally dry out (preferably in the sun) and letting it sit fallow. Many pathogens are soil born, including powdery mildew and root rot. Without this rest period, you run the risk of infecting new plants with sick soil. Allowing wet soil to dry completely will help cut down those disease spores. You can add this now dry soil to flowerbeds and lawns safely. (The dry roots and/or stumps will break down as compost. Yay, free organic matter!)

plant in pot with soil

If you want to reuse it in pots, try to remove as much of the old root system as possible to attain an even texture. Then you can add any soil amendments you like to your soil. Some amendments like worm castings improve fertility while others like perlite or peat moss affect the structure and moisture retention. In this way you can customize your potting soil to the crop. You can also mix your soil partially with fresh potting soil to make it go farther.

When it comes time to plant, use a mycorrhizal inoculant. Micro bacteria and mycorrhizal fungus form a symbiotic relationship with the roots, allowing the plants to take up water and nutrients more efficiently. This improves overall growth and stress resistance in your plants. It’s like adding yeast to bread dough; the fungal and bacterial spores bloom in the soil and will be available to aid the plant. Even for a bag that’s been in storage for a while, add these tiny helpers to invigorate the soil.

Finally, water plants in well and feed with your chosen fertilizer at the time of planting. This will encourage immediate growth and reduce plants stress. Remember, that if you flushed properly, there will be next to no available nutrients in the soil, so a good feed at planting will be welcome. Maintain a proper fertilizer regimen to keep microorganisms and plants alike healthy.

DO: Mix used potting soil in evenly with your top soil in the landscape as an inexpensive soil amendment.
DON’T: put potting soil in a hole in the landscape without adding native topsoil. Being so lightweight, it will create a water sink and just become a muddy mess with no structure.

Perlite/Clay Pebbles/Grow Stone

clay pebbles

While made of entirely separate materials, these growing medias can be recycled in much the same way. You will lose some small percentage of it to the root systems of your plants, which grow around and grip the small pieces for dear life. Other smaller roots will break off and come away with the media. These small bits of root matter will decay and release CO2, which can suffocate future root systems. They can also transfer diseases to future crops. In order to prevent this, you can either try to pick out each and every little hair individually, or you can soak your growing media with and enzyme wash. Enzyme flushes are typically used during the grow cycle as well, since they break down dead plant matter so that it can be washed out of the reservoir or made available for use by the plant. You can technically use bleach also, but enzyme flushes don’t have the harmful fumes and aren’t a threat to your skin or clothes.

After the roots have broken down, you’ll want to give it a good rinse (if trying to break down a lot of roots, trying soaking and rinsing in cycles). Last, let your medium dry out for a few days before reusing it. Much like with potting soil, letting it rest will help keep it sterile.

DO: Mix perlite in potting soil to improve aeration and moisture levels.
DON’T: mix potting soil into your hydro system.  You will hate trying to clean up that mess.

Traditional Soil

cucumber sprout in soil

And let’s not forget the most common growing media of all. True soil, aka topsoil, has been naturally re-used by Mother Nature for as long as there has been nature. Soils around the globe are in a constant cycle of heat, cold, water and organic matter that is specific to their climate. Plants native to these environments not only use the soil but help replenish it as they die and break down. Keeping invasive species under control is important to maintaining healthy native soil. To keep your top soil healthy, aerate and top dress lawns with compost at least once a year to prevent compaction. For flowerbeds, top dress with compost or mix in a bio-char soil conditioner to revitalize soil ecosystems and keep nutrients from getting locked up.

DO: water in all amendments and conditioners after application to help them settle.
DON’T: pile amendments and conditioners deeply around tree trunks and plants stems. It invites disease and bark boring insects.

Can you dig it?

Not all media can be reused. If your plants died of a soil borne disease it is always better to start fresh than risk infection. However, reusing grow media can be an effective way to reduce your inputs and make your hydro system more efficient.

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