Building a DIY Hydroponics System Part 5: Nutrients

Building a DIY Hydroponics System Part 5: Nutrients

This is Part 5 of a 7 Part Series of how to build and manage a DIY Hydroponic Lettuce System!

Other Articles in this Series:
Part 1: The Rail System
Part 2: The Support Structure
Part 3: The Reservoir
Part 4: Lighting
Part 6: Planting
Part 7: Harvesting


NEW! We've created a video course on growing hydroponic lettuce including content on how we manage nutrients and pH as well as troubleshooting for common problems you may encounter. Our goal with these courses is to make hydroponics simple. We want you to succeed!


Note about links: We have linked to certain products that we have found useful when building our hydroponic systems. Some of these links may be affiliate links and as an Amazon Associate we earn from qualifying purchases after clicking one of these. We take great care to only link to products we have found to be useful - products we would recommend to a friend or family member building this system - but you are more than welcome to use other products instead.

Supplies:

Nutrients can often be one of the most complex parts of growing hydroponically. Researching how to properly maintain nutrient levels and pH can be overwhelming. However, we've found that it's best to start simple and only move towards complexity if it's actually needed.

First, the nutrients: the two most common types of nutrients are dry mix-in nutrients and pre-mixed liquid nutrient solution. Dry mix-in nutrients are lower cost but require a little extra work up front to mix them. We've tried both with good success.

Our favorite mix-in nutrients are Masterblend Tomato and Vegetable Fertilizer. There are three parts - MasterBlend 4-18-38, Magnesium Sulfate (Epsom Salt), and Calcium Nitrate 15.5-0-0. When mixing, they should be added one at a time, starting with the Masterblend. After the Masterblend dissolves, the Magnesium Sulfate is added and dissolved, before finally adding the Calcium Nitrate. The process is pretty straightforward once you've done it a few times so this is our preferred method due to the cost savings.

We've found the pre-mixed liquid nutrients to be most useful when adding just a small boost of nutrients between water changes since they are quick and easy to add. We've used Dynagrow Foliage Pro. We've run our system exclusively on both Dynagrow and Masterblend and each have performed well.

There are other alternatives for nutrients if you prefer fully-organic growing. Organic nutrients such as fish emulsion can be used. When we first started growing indoors, we used water from our fish tank in our hydroponic system - an aquaponic system of sorts. It was a fun experiment but we found the growth rates and lettuce quality to be much lower than with commercially available nutrients. Looking back, I think the few small fish we had in our tank couldn't produce enough nutrients for the lettuce.

Next is the routine. How often do you add nutrients? When do you change water? This part has taken a decent amount of tweaking, but the routine we've landed on is:

  • Fill up the reservoir and add prescribed amount of nutrients (both Masterblend and Dynagrow have recipe on the packaging)
  • When water gets low from plant absorption and evaporation (usually after 1-2 weeks), add water to reservoir and add half of the prescribed nutrients for the amount of water that was added
  • When water gets low again, pump or drain remaining water out of the reservoir and restart the process

There are devices we've used to measure nutrient levels but we've found the above routine keeps the nutrient levels close to where they need to be. We've also found that lettuce is fairly resilient and can handle a wide variety of nutrient levels. The only time we've noticed issues is when nutrient levels get too low, usually at the end of the cycle. When the nutrient levels get low, the lettuce leaves often start to turn yellow or the new, interior leaves tip burn - the tips of the lettuce leaves shrivel up and almost appear as if they have been burned. Cycling the water at least once a month usually prevents this from happening.

In the summer we catch rainwater to use within the system. When rainwater is unavailable, such as during the winter, we use regular city tap water and treat it with aquarium water conditioner to neutralize the chlorine. This has worked well and we have not noticed any effect on the growth or flavor of the lettuce.

Our approach to pH is similar to nutrients - try simple first. Our plants have grown well at a pH between 5.5 and 6.5. Rainwater is generally pH neutral (7.0 pH) and our tap water is generally slightly basic (~7.8 pH). Simply adding nutrients to the water lowers the pH by itself so we've found the pH usually lies between 6.0 and 6.5 without special treatment. Spending more time to tweak nutrient levels and pH may result in slightly better growth rates but for a small scale operation in the home we prefer to go the simple route! You may have to pay closer attention to pH if you have very hard water or if you are growing other plants. We have used products such as pH Down to lower the pH but have found it to be unnecessary most of the time.

Now comes the really fun stuff! Planting!