pH Helpers

Greenhouse Management: What do growers need to know about the substrate after it arrives at their facility?

Frédéric Gagnon: The substrates greenhouse growers use are usually top-notch state-of-the-art products manufactured by professional companies like Lambert. However, unexpected situations can happen while running a greenhouse or nursery operation, including substrate pH drifting out of the optimal growing range. Even if the substrate is in the targeted range at the beginning of the growing season, lots of external factors like alkaline irrigation water or a mistake with the acid and fertilizer injector can influence it. The result will be a pH drifting out of the optimal range. Plants generally grow healthier and better in a specific range, which can also increase nutrient availability and accessibility. So it’s extremely important to correct it as soon as the issue is noticed. Delaying it or, even worse, not correcting it will impact the quality of sellable plants.

GM: What is the best option for growers to tackle pH issues in substrate?

FG: There are a couple options. If the pH drops below the target and you’re equipped with an injector system, the easiest and most effective way to quickly increase it is liquid lime. As it’s widely available, easy to dilute and apply, and it gives a quick reaction, that’s the first choice I have in mind. Another possibility is to top-dress the containers and pots with fine grind dolomitic limestone, but it will only be possible to do if it’s for a medium/long-term crop and with containers wide enough to allow the process. If your operation is treating the water with an acid injector, shut off this equipment or reduce the acid injection rate depending on the severity of the correction needed.

GM: How do growers address high pH in substrate?

FG: Relatively less simple options are possible for lowering the pH, but a reverse procedure should be done if pH is too high by increasing the acid injection rates. Switching to a more acidic fertilizer is also an option depending on if your location and season permit doing so. Normally, the potential value of acidity is written on the fertilizer bag. In any case, it’s necessary to take time and even additional advice to evaluate which option is best for your situation.

GM: Are there other substrate tips that you can offer?

FG: An additional quick tip that’s painless to implement is the stock rotation of your substrate. So many issues with the mix are related to a lack of inventory management, so keep in mind that first in first out is the way to go! The major component that will lose efficiency if it’s not done correctly is the wetting agent, making the substrate rewetting more difficult and your life more complicated. If you realize that you missed a moment in your stock rotation, make a small scale test first before potting thousands of containers. If it’s not successful, adding a wetting agent will resolve the situation, and you will be able to use those leftovers.