They should be fertilized at the same rate at which the plants are consuming the fertilizer. Professionals will often judge this by measuring the electrical con

They should be fertilized at the same rate at which the plants are consuming the fertilizer. Professionals will often judge this by measuring the electrical conductivity (EC) of the solution leaching from the bottom of the pot. The fertilizers are mostly ionic (excluding urea, though that becomes ionic after breakdown to ammonia), so that conductivity is roughly proportional to the root zone fertilizer concentration. These meters used to be expensive, but you can get them for a few dollars on eBay, AliExpress, etc. now. Such measurement is now de rigeur in hydroponics. It works in soil-like potting mixes too, though only the most technically sophisticated hobbyists there (e.g., many orchidists) have adopted so far. http://www.yieryitools.com/sale-9685340-high-accuracy-drinking-water-tds-meter-white-with-titanium-alloy-probe.html http://www.yieryitools.com/sale-9685340-high-accuracy-drinki...