Best Grow Medium for Hydroponics

Fertilizers, watering schedules, and seed starting are all familiar concepts to even the most inexperienced gardener, but having to choose your grow medium is a challenge specific to hydroponic farming. Let’s take a look at the best choices for growing mediums to get your garden running.

What is a hydroponic growing medium?

In traditional farming methods, the growing medium is soil. For hydroponics, the growing medium is whatever material you choose to replace soil in your garden. The purpose of the growing medium is to provide some support to your plants’ root systems and provide moisture and oxygen to the plants in between watering periods. There are both porous and nonporous options, and the best choice of medium for each hydroponic garden will depend on the type of garden you are building and your personal preference.

In soil farming, the growing medium provides nutrients to the plant directly, which is why you can more easily grow healthy plants in soil without extra fertilizer input, whereas it is difficult, if not impossible for some plants types, to be grown in hydroponic systems without the application of fertilizers. While soil naturally provides food to the plants growing in it, the growing mediums for hydroponics are chosen specifically to not provide any food to the plants.

Hydroponic growing mediums are usually made of rock or mineral based material, plastics, or very tough organic matter that will resist breaking down for a long time. Some examples of this include rockwool, coco husk, and floral foam.

What’s the best grow medium for hydroponics?

Since the main job of the growing medium in hydroponics is simply to support the plant as it grows, there are often many options that would be equally suitable for your garden. In the end, your best choice will be the option that your setup will accommodate most easily and the material you would prefer to work with.

Best rock/mineral mediums

*Grow rock: Grow rock is derived from clay. The clay is heated and expanded to become small balls of porous material that stores oxygen for your plants.

*Rockwool: Rockwool gets its name from its production. Rock is heated up and “spun” into tiny strands so it resembles wood, similar to the look of steel wool.

*Perlite: Perlite is very lightweight and porous rock. Within its pores, it can store plenty of oxygen for your plants’ roots as well as small amount of water.

*Vermiculite: Vermiculite is similar to perlite, but is much better at retaining water and less so at storing oxygen. Vermiculite is better for water-hungry plants that could benefit from having residual water stowed away for usage in between watering times.

Check out a more detailed video on the differences between vermiculite and perlite here:

Growstones: Grow stones are also derived from clay and sand, in the form of recycled glass. Its porous nature allows it to store both plentiful oxygen and water for your plants.

Sand: Sand, to put it simply, is made up of very small bits of rock and minerals. Its small grain size allows it to pack quite efficiently and hold onto water for a longer time than rock mediums of larger grain size, such as gravel.

Gravel: Gravel is a cheap option for growers looking for a nonorganic growing medium that won’t hold onto moisture. You can purchase gravel from landscaping companies, some hydroponic supply stores, or, in some areas of the country, directly from sand and gravel quarries. Most home and garden stores sell gravel, but only in small quantities for relatively high prices, so it is recommended to look for other purchasing options. Online ordering is another option for gravel supply, but with gravel being heavy, you may find that the shipping costs get quite high.

Best synthetic mediums

Floral foam: Floral foam holds onto a lot of water, and it’s easy for it to hold onto too much for too long and cause root rot. Floral foam is not an ideal medium, but it can be used in a pinch for seed starting.

Polyurethane foam: Polyurethane foam can be used as an alternative medium for the specially designed grow foam, such as floral foam and Oasis cubes. Like the others, it can be used for seed starting, and it widely available at home and garden stores, usually in the insulation section, so it can be a good option for those in areas where the specialty products are unavailable or very expensive.

Water-absorbing polymers: Similar to the material found inside of disposable diapers, water-absorbing polymers are a completely synthetic product with the ability to store large amounts of water for a long time with relatively little volume of product. These come in various orb-shaped sizes in garden shops, and because of their spherical shape, allow for ample room to accommodate an oxygen supply for the root system.

One of the best and most popular polymer-bound plugs would definitely be the Rapid Rooter. Check out our post for more info on that.

Oasis cubes: Oasis cubes are a specially designed product to provide an environment for hydroponic seed starting. They are made of a type of garden foam that has compartments in the middle to provide optimal germination conditions for your seeds.

Best organic mediums

*Coco husks: Coco husks, or coconut fiber, are a very popular choice for gardeners both in and out of hydroponics, and it can be found in almost any store dealing with home and garden. Coconut fiber does not retain moisture.

Pine bark or shavings: The key to using pine products is to make sure they have been aged and composted to eliminate all of the material in the wood that will decay quickly and add excess nutrients to your plants that could overload and harm them. Pine bark won’t retain much moisture and drains quickly.

Rice Hulls: Rice hulls are the discarded “shells” that come off of rice grains during processing. In areas known for rice production, rice hulls may be an easy-to-find and cheap options. Similar to pine products, it’s important to choose a composted version. Gardeners using rice hulls usually combine them with pine products or other growing mediums.

* denotes the most commonly used growing mediums by hydroponics gardeners.

How do you grow a soilless medium?

Growing in a soilless medium requires the gardener to understand a couple things. It should be recognized that your plants will fully rely on you adding fertilizers and supplements to grow. In soil farming, you can get away with a little more or a little less added nutrients, because a healthy, nutrient-filled soil will almost always make up for anything you miss, and the more open system allows overly-concentrated nutrients to drain away from the roots and lose some of its potency in the surrounding soil. A soilless medium will not provide that buffer, so a soilless gardener will have to be on top of whether they are properly mixing and applying plant food.

Further, know your plants’ water sensitivities. Soil holds excess moisture after watering, but some soilless mediums will not. Understand how your medium’s water storage compares to soil so you can properly adjust your watering schedule to accommodate your plants’ needs. For especially water-hungry plants, such as tomatoes, you may find that growing mediums with the ability to store water in between applications will be very beneficial.


Can I use Miracle-Gro™️ in hydroponics?

It is possible to use some Miracle-Gro products in a hydroponics garden, however not all products will contain the necessary nutrients in acceptable levels, and you risk under-feeding or over-feeding your plants if you aren’t careful. Check the nutrition facts and compare those to the requirements of your specific crops. All in all, though Miracle-Gro can be used, it is certainly a second choice to the specially formulated hydroponic nutrients solutions on the market.

Can you overwater hydroponics?

Before we answer the question, let’s look at what actually happens when you overwater a plant in traditional soil farming. Every plant needs both oxygen and water to be available to its roots. Overwatering isn’t necessarily just giving a plant more water than it needs, but it is applying so much water than you fill up all the places in the soil that held the roots’ essential oxygen supply. When the water doesn’t drain away or evaporate quickly, the lack of oxygen suffocates the roots and causes root rot.

Knowing this, you’ll see that it is definitely possible to mistakenly deprive your plants of oxygen, although the problem is much less common in hydroponics than soil gardening. If you neglect to properly aerate your system or use a growing medium that holds onto too much water for too long, you may encounter problems similar to overwatering. Being sure to invest in the proper equipment and thoroughly research the needs of your preferred crops will easily prevent root rot problems.

Can I use gravel for hydroponics?

As mentioned earlier, gravel is certainly an option for a hydroponics system if you’re in the market for a nonporous growing medium. Gravel comes is a variety of different sizes, providing an option for gardens on every scale, and it can be found in large quantities for a relatively cheap price.

Understanding the properties and purpose of your growing medium are essential for choosing the best option for your hydroponic garden. With so many products of widely varying materials available for use, there is truly an option for every farmer, every budget, and every set up.

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