Timing Soil Inputs

Getting your soil right for planting can often leave many growers scratching their heads in confusion. There are numerous options available on the market and knowing when to add inputs to your soil is crucial.

Let’s explore the “WHENs” of soil inputs:

When to test the soil

Before you plant a single seed or buy a product, you need to know what’s going on beneath the surface. A soil test can tell you what your soil lacks or has too much of. Getting soil tests in the fall after harvest or early spring allows you to correct imbalances way ahead of planting time. Testing early gives you time to understand your soil’s nutrient profile, pH, and organic matter content.

For cannabis and other nutrient-hungry crops, regular testing (at least once per season) helps guide mid-season inputs, especially before flowering. Other growers may only need to get their soil tested every three years.

When to add fertilizers and amendments

Whether you want the greenest lawn in the neighborhood or a lush garden this year, adding fertilizers and other soil amendments can make all the difference. Once you have your soil test results back, you’ll be able to make the right fertilizer choices for your particular soil and plants.

You can apply slow-releasing fertilizers in the fall or spring to provide consistent nutrients over time. If you notice that your plants are weak and yellowing, you may need to give them a boost with a fast-acting fertilizer. This can be done every 3-4 weeks during the growing season. However, be cautious when applying fast-acting fertilizers, as they can cause damage and even kill your plants.

Apply any additional soil amendments, such as compost, manure, rock dust, or other minerals, based on your soil test results. You can do this before you start planting or top dress throughout the growing season as needed.

When to add microbial inoculants

There are a number of microbial inoculants you can add to your soil from biofertilizers to biostimulants. However, it’s always best to apply them at the beginning of the growing season so the microbials have enough time to colonize the root zone early and form symbiotic relationships as roots begin to grow.

For transplants, it’s ideal to apply inoculants directly to the root ball or into the planting hole, ensuring close contact with the roots. In systems where the soil has been tilled or disturbed, you’ll want to reapply your inoculants to reestablish the colonies. Growers should also consider reapplying inoculants after using fungicides or sterilizing agents that may kill or reduce the microbes in or on the soil.

In cannabis cultivation, microbial inoculants are particularly valuable during the cloning and transplanting phases. Mycorrhizal fungi can significantly enhance phosphorus uptake and improve stress tolerance, both of which are critical for strong vegetative growth and successful flowering later on. Because these organisms thrive in moist, aerated soils, timing applications with irrigation can also help them establish more effectively.

When to add Beneficial Nematodes

Pests under the soil are often the most challenging. Luckily for growers, they can add an exceptional underground ally-beneficial nematodes-to support their operations. Beneficial nematodes should be applied in when the soil temperatures are between 42°F – 95°F. The warmer the soil, the more active the nematodes, and the greater the protection and results. Also, avoid applying them during dry spells or in full sunlight, as UV rays and dehydration can cause them to die quickly. Water the soil before and after application to help them establish.

Knowing when to apply the nematodes depends on what pest you are trying to control. For example, if you're targeting fungus gnat larvae in greenhouse cannabis or vegetable production, it's best to apply nematodes early in the season or just after transplanting, just before adult gnats start laying eggs. If you're managing root-knot nematodes or root weevils in perennial systems, applications are most effective in late spring when larvae are actively feeding near the root zone. In turfgrass or pasture settings, nematodes targeting white grubs should be applied in late summer or early fall, when young larvae are close to the soil surface and most vulnerable.

Each pest has a specific life cycle stage that’s most susceptible to nematode predation. Proper timing ensures that beneficial nematodes find their targets before they cause significant damage, and before they retreat deeper into the soil where nematodes are less effective.

Final Thoughts

Treat your soil right, and you’ll reap huge benefits in the end. Improving the soil won’t happen overnight, as great soil health starts long before you plant your first seed. By testing your soil early, timing inputs to match plant growth stages, and using biology-based inputs like microbes and nematodes, you set your crop up for long-term success.

So, don’t just feed your soil. Observe and listen to it.  It might just tell you exactly what you need.