Any nutrient company worth their salt (no pun intended) are going to provide their end users with a detailed feed schedule. This is usually a bit different than the directions which are provided on the bottle as these will show a more simplified application. The application rates on a feed schedule are more complex and shows all of the products in the line used in conjunction with one another. This is not to say that the bottle directions are wrong, only that if results are to be maximized the product should be used as part of the larger feeding schedule.
A feeding schedule is the culmination of years of growing experience and formulation technology at your fingertips, and while a lot of work has gone into it there are limitations.
- With each component in a product line having different nutritional profiles, a proper feeding schedule will adjust the ratios of the various nutrients so that the plant will get the correct nutrition at the right times during its life cycle. For example nitrogen levels increase over the vegetative cycle and then drop off once flowering begins. From there phosphorus levels rise for the remainder of the life cycle.
- Feeding schedules are based on optimal water sources. Since there are usually some minerals dissolved in water this should be taken into account and the schedule adjusted accordingly. For example a moderate level of calcium (around 20-40 mg/l) could result in less Cal Mag product such as Calnesium or Organical Magic being required. A Hard Water Micro formulation should be considered if the amount of calcium is excessive. For more information on water quality check out the previous blog post Effects of Water Quality in Hydroponics
- Genetics are a huge unknown factor when it comes to publishing a feeding schedule. Some strains are sensitive to salinity and so can be inhibited by too much fertilizer, while others can tolerate high levels and will grow faster when more nutrients are available. Since this is beyond the scope of the manufacturer it is recommended that the grower experiment to optimize the schedule to the strain. Leaf curl is a sign that levels are too high while a fast drop in levels on a nutrient meter will indicate feeding levels could be increased.
- The chart will usually show target nutrient levels. In the case of the one published by Future Harvest Nutrients we use the 0.5 scale. As I have previously mentioned it the blog post The Confusing World of Nutrient Solution Measurements there are a lot of limitations to nutrient meters but unfortunately it is the only measuring system available at an affordable price to consumers. There can be confusion in the fact that the levels expressed in the later stages of vegetative growth are usually higher than in most stages of flowering. The actual amount of nutrient isn't necessary higher at this stage but we do get higher readings because potassium nitrate is a really good conductor of electricity and there's higher ratio of it during late vegetative than at any other time.
A well researched feeding chart can be a very powerful tool in the hands of a grower, but there are some factors which we simply don't know when we're writing them. Our best advice is to start with what is published, assuming that the water source isn't too bad and see how the plants react to it. If it is too strong then cut everything back by 10%. Should the plants go through the feed faster than anticipated then try increasing everything by 10%. Once these adjustments are made, observe and make further tweaks if necessary.
To view the Future Harvest Nutrients feeding schedules click here.