Cannabis Fertilization Requirements at Each Stage of Growth
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Cannabis Fertilization Requirements at Each Stage of Growth

Assume there is virtually no nutrition in your potting mix unless it contains compost or coconut fiber.

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March 20, 2019

While your specific growing situation and especially your varieties will likely lead to adjustments in fertility inputs, these general guidelines have produced many successful cannabis crops. 

1. Seedling or Cutting

The plant can live for a time off of nutrients in the seed. Use minimal or no fertilizer in the early seedling stage. Rooted cuttings are often deficient after propagation. Feed both very gently with a 1-1-1 balanced formula at about 100 ppm for each once there is adequate root development.

2. Vegetative Growth

The vegetative growth stage averages 4 weeks, but can be as short as 2 weeks or as long as 2 months depending on environment, variety and container size. After transplant, kick feed rates up to about 200 ppm N, 120 ppm P2O5 and 200-250 ppm K2O for vegetative growth. 

3. Early Bloom

Extra calcium and magnesium are important additions at the start of the bloom stage to produce strong sturdy plants with heavy buds and a robust root system. Shift to roughly 200-250 ppm N-P2O5-K2O at the start of bloom. There should be a little boron in the feed program by the start of blooming. Definitely apply more potash than nitrogen during all bloom stages. Reduce nitrogen somewhat more if plants are large.

4. Late Bloom

At week 5 of bloom, reduce N applications to about 125 ppm, and make sure you have adequate phosphorus once the calyx or sepals form.  Use about a 1 to 1.5 ratio of N to K2O in the last four weeks of bloom. Potassium silicate may help strengthen plants during the latter part of the blooming cycle. 

5. Flush

At bloom week 9, most growers flush with clear water with no added fertilization. Use some calcium nitrate and kelp extracts if possible throughout the crop.

You’ll want to monitor pH and EC, at least weekly. It’s a good idea to run a leaf analysis at an in-state lab at about bloom set, but check with your lab about the legalities involved. Throughout production you water with only clear water once every 10-14 days, depending on EC readings.

Assume there is virtually no nutrition in your potting mix unless it contains compost or coconut fiber.