When my wife and I first got into growing plants with hydroponics, we noticed we needed to use a specialized liquid fertilizer. 

This seemed extra to us since we already had some normal fertilizer on hand. Why waste money in buying another type?

Fortunately, I did more research into this topic and saved myself a lot of frustration before using the common fertilizer without thinking. 

While it’s possible to use normal fertilizer for hydroponics with the right mixture of water and Epsom salt, it doesn’t work as well. Hydroponics need a quick-releasing form of nitrogen, such as nitrate, as found in most liquid fertilizers, while common fertilizer uses urea, a form harder to absorb. 

Let’s dig into the details and how to mix up a fertilizer solution for hydroponics. 

using normal fertilizer for hydroponics

Can You Use Normal Fertilizer With A Hydroponic System?

Think about a typical soil growing setup and a hydroponic one. 

In a hydroponic system, the plant dangles its roots into water and air. It receives its nutrients from a water solution and grow lights. 

There is no soil. 

The moisture, air, and light combination makes the plants and containers prone to mold and algae. It needs sterile water, low in microbes. 

Normal fertilizer has a lot of these bacteria. Using it as is would cause an issue. 

In soil, it’s not as big of a deal because the soil is there to spread and absorb the bacteria. 

The bacteria will help break down other dead materials in soil and send more nutrients to the soil. 

In hydroponics, nothing’s there to break down except the plant. 

Soil fertilizers are also intended to work over the long run. It takes a while for all the nutrients to be absorbed. 

You only usually apply fertilizer once to the soil at the beginning of the growing process.

In hydroponics, we add nutrients to the water solution regularly. 

The easiest way to get started with hydroponics is with a pre-made system. Check out our review of the best AeroGarden for lettuce and small herbs.

What Nutrients Are In Fertilizers?

All fertilizers need to deliver nitrogen to the plants (more on needed plant nutrients later). 

Common fertilizers contain urea and ammonium salts, which are processed slowly by the bacteria and microbes in the soil. 

Without the bacteria, it won’t be processed, making a lot of the nutrition useless to a hydroponic plant. 

Instead, hydroponic plant food is made up mostly of nitrate salts.

Nitrate salts dissolve in water and pass through the roots much easier than the other two forms of nitrogen. 

So why don’t all fertilizers use nitrate salts? The salt is also washed easily by rain and poses a danger to groundwater in high amounts. 

Ammonium and urea are also a problem for hydroponic plants because if you manage to deliver them to the roots, the high concentration will make the plant acidic and toxic. 

Nutrient concentration is always an area of concern, even with liquid fertilizers, which is why you’ll only need to use a few drops for your hydroponic reservoir. 

Are you interested in building your own? Check out these DIY hydroponic reservoir ideas in our article here (with pictures!).

What Nutrients Do Plants Need From Fertilizer?

We’ve talked about nitrogen a lot, but plants need a few other nutrients from their fertilizer for good growth. 

Every type of plant food (soil or hydroponic) needs the big 3 nutrients to facilitate photosynthesis. 

Be sure to check the packaging to make sure these are in the product you buy. 

Nitrogen (N): Yes, nitrogen is the big one, as we’ve touched on before. Nitrogen is critical in helping make plant cells and chlorophyll, both of which are a must for effective photosynthesis. 

40-50% of plant cells are made of nitrogen, and it promotes healthy foliage and increases other mineral absorption through the roots. 

Phosphorus (P): Phosphorus is another essential nutrient for photosynthesis and root development. It helps create nucleic acid in cells, and when your plant flowers, there’s a distinct uptick in phosphorus usage. 

This nutrient is also important in helping process calcium, which is also important in plant development.

Potassium (K): We hear about potassium a lot like humans, but it’s important for plants too, so the fertilizer needs to help the water or soil bring potassium to the roots. 

It improves the food quality of the plant, helps with photosynthesis, and increases internal liquid movement. 

This last one is a fancy way to say it helps deliver more nutrients throughout the entire plant. 

While there are other minerals and elements in fertilizers, these 3 are the big ones to watch out for.

Here’s a list of good nutrients and minerals to be on the lookout for: 

Nitrogen (N)Manganese (Mn)
Phosphorus (P)Boron (B)
Potassium (K)Zinc (Zn)
Calcium (Ca)Copper (Cu)
Sulfur (S)Molybdenum (Mo)
Magnesium (Mg)
Iron (Fe)

How To Use Common Fertilizer In Hydroponics Safely

If you do want to use your common soil fertilizer with a hydroponic system, follow these steps to do so safely. 

Fill Water

Fill up your hydroponic reservoir, and keep track of the number of gallons you use. 

If using tap water, make sure the water isn’t high in chlorine or chloramine. An easy way to remove these chemicals is to leave a cut lemon to soak in the water for 24 hours before adding it to the solution. 

Room temperature water is ideal, but if you leave it out for 24 hours before adding it to the hydroponic tank, it’ll be room temperature anyway. 

Add Fertilizer 

When the water is in, add 2 tablespoons of fertilizer for every gallon of water in the tank. 

If possible, remove any large, visible chunks of the fertilizer before adding it to the water. 

Mix In Epsom Salts

Now, we need to help the fertilizer dissolve into the water by adding 1 teaspoon of Epsom Salt (magnesium sulfate) for every gallon of water. 

Stir the water/fertilizer/salt mix until the water looks completely liquid and there are no traces of solids. 

You may wish to run the water through a strainer at this point to ensure little to no solids. 

Solids may clog up your pumping process. 

Add Water When Half Empty

At this point, your nutrient solution is ready. Use the water as you would any other nutrient-rich water for a hydroponic system. 

The water will be absorbed by your plants. When the water is half gone, add more water to the tank. 

Warning! Do not add more fertilizer. This may create issues with nutrient toxicity from too high of a concentration of the minerals. 

Refill as needed. 

Replace Water Solution Every Two Weeks

After two weeks, dump out all of the water, wipe down your tank, and repeat the process. 

Most actual hydroponic fertilizers only require a full change every 4-6 weeks, but with this homemade mix of soil fertilizers, you’ll want to start over every two weeks.

This will prevent pockets of highly concentrated nutrients while also ensuring the water overall has a good balance of nutrients, salt, and acidity. 

Failing to do this may cause buildups of salt, wrong pH levels, or low nutrition, all of which may kill your plant.