The hydroponics industry has been abuzz in recent months with discussions concerning plant growth regulators (PGRs), hormones that are used ubiquitously in the horticulture industry. These products are used throughout the lifecycle of plants, whether we are using auxins to produce rooted cuttings or paclobutrazol to retard the vertical growth of plants. Most of the conversations I have participated in recently have revolved around one of three dimensions: the use and safety of these products, whether it is better to use natural or synthetic hormones and why these products are so expensive to purchase. Any one of these topics would necessitate many more column inches than are available here, so I will primarily focus on a single topic that has ramifications across the aforementioned dimensions: making a natural plant growth regulator cheaply.
From the outset, I should make my personal philosophy clear: I advocate using plant growth regulators to efficiently optimize plant growth, regardless of whether they are derived with natural methods or synthetically created. Since I run my own hydroponic horticulture business and keep a vigilant eye on my cost structure and profit margins, I generally choose to create my own PGRs naturally than to buy them. While this might sound daunting, the technique I will describe hereafter provides cost savings across the board for interested growers.
The basic method can be summarized as follows: recirculate your nutrient solution for an extended period of time (e.g. beyond one year) to allow organic compounds exuded from the roots, including PGRs, to accumulate in the nutrient solution. So, rather than periodically discarding your complete solution, you should simply top-off your solution with pure water or a diluted-nutrient solution as necessary to maintain a set electrical conductivity level. As the continuously-recirculated solution builds up natural PGRs, your canopy size per plant will decrease—but your plants will mature at a faster rate. To maximize this growth strategy, it is recommended that you adopt a continuous production system rather than a batch production strategy.
This might sound too simplistic to work, but I assure you that the science is sound. After reading some technical briefs from NASA, where a team of researchers grew potatoes with the nutrient film technique for over a year without changing the nutrient solution, I attempted this with my own crops. I grew three types of lettuce in flood-and-drain tubes for a year without completely changing the nutrient solution and was amazed at the differences between the early plantings and those near the end. As you can see from the pictures, the plants became smaller over time, but I didn’t lose yield over time.
It amazes me that I could save so much money on nutrient solution and growth regulators by growing my own PGRs so to speak; however, the major tradeoff is that a lot more planning and effort is needed to rationally manage your nutrient solution parameters. In any event, you can be sure that your PGRs are naturally produced and are appropriate for the crops you are growing.