For a plant like lettuce which is 95 percent water, ppm is the most crucial factor.
During the complete growth cycle of the lettuce, you will have to maintain the right ppm for the nutrient solution that you use in the hydroponic system.
The ideal ppm for hydroponic lettuce has to be in the range of 560-840. Anything lower or higher will affect the growth of the lettuce.
Here I am going to provide you with a complete guide on ppm for hydroponic lettuce, which will help you understand what it is, how you should maintain and also the issue that you can face if the ppm is high or low.
What PPM Means in Hydroponics?
PPM is the amount of contamination or nutrient present per unit volume of water.
As I mentioned earlier, ppm shows the number of contaminants or nutrients in the water you feed your crop.
What does this mean for hydroponic lettuce?
Knowing the ppm, you understand whether your plant is getting proper nutrients.
High ppm means that there is ample nutrient in the water, and low means vice versa.
Whenever the ppm falls beyond the required amount, you are supposed to add a nutrient solution.
Also, you should ensure you do not add beyond the required amount. Otherwise, you will be overfeeding your lettuce.
How to Maintain The Correct Amount of the PPM?
Knowing what the ppm is, is not enough. You must know how to maintain the right ppm. Here I will provide a step-by-step guide to maintaining ppm for hydroponic lettuce.
1. Know the Base
We generally use household tap water for hydroponics, which already has contaminants and chemicals.
So if you don’t know the base ppm of water, you won’t be able to determine how much nutrient is there in the water. You will always be underfeeding your crops.
Know the base ppm because you will have to subtract it from the total ppm you get after adding the nutrients.
This way, you will know exactly how much nutrient is in the water.
Take a reading before you add any nutrient solution. Also, you can take a reading of the tap water you get in your house regularly to know the average number you will have to subtract from the total ppm reading.
2. Know The PPM For Nutrient Solution
The PPM reading for a nutrient solution from a different manufacturer is different. So don’t use the same reading if change nutrient solutions regularly for a single crop.
Also, I suggest not blindly trusting the recommended ppm from the manufacturer.
Have your chart for ppm reading and see which range benefits the lettuce.
One thing that will help you is after you have added nutrient solution, always take note of how it affects the plant. Experiment with the optimal ppm range for each nutrient solution from different manufacturers.
3. Adjust PPM
After adding the nutrient solution, take readings to ensure it isn’t going down. If your lettuce crop is underfeeding, you can add the nutrient solution. As the plant grows, they tend to underfeed.
But when do you need to adjust the ppm for hydroponic lettuce?
For that, you need to be aware of the growth cycle of hydroponic lettuce. Most varieties have a growth cycle of 45 to 55 days.
If you are growing something like romaine lettuce, the growth cycle can be around 75 to 85 days.
For more detail, you can check out our article on the best hydroponic lettuce to grow.
Once you have an idea of the growth cycle, just divide it by 3. This is not something scientific, but that is what I generally use.
Let’s say the growth cycle is 45. By dividing it by 3, we get 15. And if it is 75 days growth cycle, you get 25 after dividing it by 3.
So 15 and 25 are the days after which you have to adjust your PPM. Mostly you will be increasing the ph every 15 days or 25 days.
I suggest bumping up the PPM by 200 each time because the plant is growing, and the requirement for nutrients also increases with the growth stage.
What Happens if PPM is Too High?
If you are adjusting your PPM regularly, you won’t have to worry about issues due to improper PPM. However, in case you notice that PPM is too high, your lettuce may face issues like yellowing, browning of leaves, wilting, etc.
It is wise to check up on the PPM every couple of days to just keep track of what you are feeding your lettuce.
If you find that PPM is too high, you should empty the tanks and all the reservoirs. And make a fresh batch of nutrient solution keeping all the points that I mentioned above.
You should have a routine in places that track the ppm for hydroponic lettuce. And whenever you change anything, be it a nutrient solution, etc., test it on a few plants and see the change. If it is positive, then apply it whole crop.