The best fertilizer for your hydroponics project will depend on several factors including the plants you are growing, the medium you are using to support them, and the stage of the plants’ growth cycle.

Your own level of expertise is also relevant with some fertilizers more suited to beginners and others to experienced hydroponic growers.

Before choosing a fertilizer for hydroponics, you should think about the specific needs of your plants and your own preferences in terms of productivity, cost and ease of use. Our simple guide below takes you through the main options.

You should also read: Best Hydroponics System On The Market

Why Is Fertilizer Used In Hydroponics?

Traditional agriculture and hydroponics, both require the presence of a specific balance of three key elements, nitrogen (N), potassium (K) and phosphorus (P), in order for plants to develop, flower and produce a crop. Fertilizers all provide these three elements, varying in in exact composition and form. 

Why Is Fertilizer Used In Hydroponics?

Soil already contains a certain level of nutrients to support plant growth and fertilizers are used in traditional agriculture to supplement this natural level. In hydroponics, there is no soil involved and you will need to introduce all required nutrients into your system in the correct proportion and at the correct pH (acidity or alkalinity) level.   

For the best growth outcomes, you should monitor and maintain N, K and P concentration at optimal levels throughout the plants’ growth cycle. This could mean adding more or less fertilizer in order to adjust the concentration and ratio in your hydroponics system. Uptake of N, K and P by your plants depends on the stage of the plant’s growth cycle. 

Can I Use Ordinary Fertilizer In Hydroponics?

Overall, use of ordinary fertilizer is not recommended in hydroponics. Hydroponics differs from traditional agriculture in several important ways. Most obviously, in hydroponics, there is no soil present. This matters when choosing a fertilizer for several reasons.

Firstly, alongside the primary nutrients N, K and P, there are a range of secondary nutrients and other trace elements which support healthy plant growth. These elements are not necessarily included in ordinary fertilizer because they are already found naturally in many soils. They include:

  • Magnesium, Sulphur, Calcium (secondary nutrients)
  • Iron
  • Boron
  • Molybdenum
  • Manganese
  • Zinc
  • Copper

By using an ordinary fertilizer you could be depriving your plants of these elements. With a specific hydroponic fertilizer you add these elements to your hydroponics system directly and in proportions suitable for your plants. 

Secondly, hydroponic media do not behave in the same way as soil in terms of mineral retention and availability. A small amount of mineral salts will be present in all fertilizers but levels are higher in regular fertilizer. 

Important: This is less important in traditional agriculture where salts could be held safely in the soil or washed out by rain. In hydroponics the same salts could accumulate to dangerous levels in contact with plant roots, causing a buildup which restricts plant growth. Salt levels in dedicated hydroponic fertilizers are therefore carefully balanced to avoid this.   

Thirdly, hydroponic fertilizers are pH balanced and normally contain a buffer which will keep the system’s pH level within a safe range. Ordinary fertilizers, with differing pH levels and no buffer, could push the pH of the system to a damagingly high or low level, potentially retarding or killing plants. 

Why Does The Stage Of The Growth Cycle Matter When Choosing A Hydroponic Fertilizer?

Your plants may benefit from a different balance of N, K and P at different stages of their development:

N: Nitrogen

Helps to build the internal structure of plants (e.g. their cells) and to produce the green pigment chlorophyll which catalyzes photosynthesis, the plant’s energy producing process).

Nitrogen is especially important in the early growth phase in order to develop healthy leaves, stems and roots.

P: Phosphorous

Supports the plant’s photosynthesis, root development and blooming. Uptake increases when a plant is producing flowers.

K: Potassium

Supports photosynthesis, and the healthy circulation of sap within a plant. These functions are important for ensuring high fruit quality.

What is the cheapest fertilizer for hydroponics?

The cheapest nutrient solution for hydroponics will generally be in solid form and should be dissolved and diluted with water before use in your hydroponics system. Liquid fertilizers offer convenience and ease of use, especially when ready-mixed, but are usually more expensive than solid fertilizers.    

Some hydroponic nutrient fertilizers are already fully combined and ready to use. Others come in three parts and must be used in combination. The ratio of parts and frequency of use will vary in accordance with manufacturer instructions and your own needs. 

Different brands may contain a slightly different balance of trace minerals, and some types of fertilizer might be tailored to optimize the growth of particular crops or types of hydroponic system. Prices could vary to reflect this.   

Buying your fertilizer in larger containers or in bulk could save you money compared to buying small containers more often. 

Ordinary fertilizer may be cheaper than hydroponics fertilizer but will not be optimized for hydroponic growth, presenting potential problems described in this article. This could result in sub-optimal plant growth which does not give value for money. 

The Final Word…

There are many excellent fertilizer options available for hydroponics. 

If you’re just starting out in hydroponics, you may want to begin by using a simple one-part hydroponic solution which can be added to the hydroponic system without further preparation, following the manufacturer instructions. 

As a more experienced grower, looking to maximize the quantity or quality of your crop, you may wish to tailor use of a three-part solution according to your needs. 

Hydroponic growers seeking the best value for money may want to consider buying a solid hydroponic fertilizer in bulk.

In all cases, you need a fertilizer which contains an optimal growth ratio of nitrogen, potassium and phosphorus, along with a balance of the key trace minerals normally found in soil.

Remember, using a normal fertilizer is not recommended for hydroponic systems.

Further reading: Is Hydroponics Cheaper Than Soil?