What measure can help maintain optimal oxygen levels in a grow medium?

Using the right growing substrate that promotes air aeration is crucial for maintaining optimal oxygen levels in growing mediums. A well-aerated substrate allows for the proper circulation of air, ensuring that the roots of the plants have access to the oxygen they need for healthy growth and metabolism.

When a growing medium is selected appropriately, it facilitates the creation of air pockets that prevent compaction and waterlogging, which can lead to hypoxic conditions (low oxygen levels). This is essential because plant roots require oxygen for respiration and nutrient uptake. Without enough oxygen, roots can become stressed, leading to poor plant health and growth.

The other options do not directly contribute to maintaining optimal oxygen levels in the growing medium. For example, frequent watering can lead to oversaturation, which might suffocate roots by eliminating air gaps in the soil. Growing plants in shade may protect them from direct light but does not support healthy oxygen levels in the substrate. Similarly, adding more fertilizer does not address the aeration of the medium and can sometimes exacerbate nutrient imbalances and root health issues.