All gardeners need to consider the environmental impacts that they may have by choosing one method or substrate over another. Many staples of hydroponics and soilless container growing come from strip mines that destroy natural habitats like rain forests or peat bogs.
Media such as perlite, vermiculite and expanded clay pellets (hydroton) all come from strip mines. Strip, or surface, mining involves moving thousands of tons of earth to dig out the desired mineral. These mines use large amounts of energy and often heavily pollute their surroundings, leaving behind large areas of barren bedrock unfit for any sort of cultivation.
Reusing a non-renewable medium like clay pellets cuts back on its negative impact, but renewable media beat reused clay any day. Here’s a list of some viable soilless mediums that come from renewable plant resources like rice, coconuts or pine trees.
Parboiled Rice Hulls
Parboiled rice hulls have drainage properties similar to perlite and provide additional nutrients like manganese and silicon. Some research says plants grown using rice hulls outperform those grown in perlite. The pH of rice hulls should fall between 5.7 and 6.5. Soak the rice hulls in a nutrient solution for 24 hours before using and test the pH to see where it lies, adjust appropriately and continue to use the same amount of pH up or down to maintain that level in the future.
Coco coir is a tried and true soilless medium, nothing new here. Coco tends to release potassium into the soil and may hold onto phosphorus and calcium. Some growers choose coco-specific nutrients due to any potential calcium or potassium imbalances, but normal hydro nutrients should work fine as long as you keep an eye out for calcium deficiencies. Make sure to periodically flush to prevent salt build up and nutrient lockout.
Composted Pine Bark
Pine bark for soilless growing normally comes composted so it doesn’t tie up nitrogen. To prevent the bark from becoming water logged, you may need to use ebb and flow techniques. Mixes of 70 percent pine bark and 30 percent rice hulls can provide optimum drainage and water retention properties.
Several studies have found that pine chips can replace perlite in soilless mixes and have similar drainage properties to clay pellets, gravel and perlite. When growing with pine chips, it’s important to monitor pH and ppm levels of the runoff, the pine chips may absorb some nitrogen. If you spot a nitrogen deficiency, you may need to add 100 ppm extra N.
Pine shavings have appropriate drainage properties, and you can use them on their own as a hydroponic medium. Similar to the case with pine chips, you may need to monitor nitrogen levels.