If growing indoors using small litre plant containers you may need to add light feeds of veg (grow) nutrients after a few weeks. Conversely, if growing in large containers of quality soil with slow release organic nutrients you may not need to add any additional nutrients at all, or only at the end of bloom.
If growing in hydroponics the plants are totally dependent on you for all feeding requirements from seedling to harvest. Unfortunately, there isn’t a single simple answer for when you need to start feeding your indoor cannabis plants. Everything depends on your specific grow method and conditions.
Cannabis nutrient feeding schedule by growth stage
As the cannabis plant grows the required nutrients also change. In early growth a diet rich in Nitrogen supports growth of leaves, branches and roots. In the cannabis flowering stage, more nutrients are required in general, with a specific requirement for more Phosphorus and Potassium.
It’s important to state that each plant grown from cannabis seed is different and should be treated as an individual. Even when growing several plants from the same variety of best cannabis nutrients, the experienced grower may notice that the plants have subtly different nutrient requirements.
General advice on cannabis nutrients and feeding schedule
It is better to slightly underfeed your cannabis plants than to over feed them, which can cause permanent damage in severe cases. The nutrients charts provided by the supplier should be treated as a guide rather than firm rules. Each plant can have different feed requirements, even when grown from cannabis seeds of the same strain.
In general, it is better to err on the side of caution and slightly underfeed your plants in order to establish the ‘starting point’ for nutrient concentrations. You can always increase nutrient levels in subsequent feeds. But you can’t undo the damage done by over-feeding your cannabis plants.