Always use a Mycorrhizae soil amendment, preferably one that contains Bacillus bacteria, this will address any contaminants in the growing medium that may find their way in. Mycorrhizae fungi form a symbiotic relationship with plant roots that will encourage strong healthy plants. Don’t make the mistake of only paying attention to the part of the plant that is above the ground. The part of the plant that is under the ground is more important and will determine the health of the plant above the ground.
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What is the Best Growing Medium for Indoor Horticulture?
Don’t throw your many away on any pre-blended store bought growing mediums. If you are growing indoors use a mixture of Peat + Perlite + Pulverized/Powdered Lime. Mixing these yourself will save you a lot of money and provide you with 10x the amount of usable growing medium. You will not have problems with fungus gnats or soil born pathogens that lead to disease in plants when using an inert medium like this unless you introduce them to your growing space.
Amending Growing Mediums
Peat is naturally quite acidic (pH 3.5-4.5) and will drift to become even more acidic over time. Lime must be added to raise the pH. On average, you will use 2 Tablespoons of fine powdered lime per gallon of growing medium or 1 Cup per cubic foot.
1 Cup = 16 tablespoons
1 Cubic Foot = 7.5 gallons
Without the addition of lime, or not enough, nutrients such as phosphorus and potassium will become highly available in a low pH growing medium. This can lead to signs of nutrient toxicity as well as deficiencies of other nutrients, most commonly Iron. The correct degree of acidity for growing mediums is a pH of around 6.5. If your growing cycle is longer than 3 months you may need to compensate by watering with a solution of Lime + water to raise the pH of the growing medium. Use a mixture of 1 TSP lime per gallon of water every 2 weeks. This will adjust the growing medium pH by 1/2 point.