Organic Nutrients for Soilless Gardening

Plants need nutrients and minerals to thrive, flourish, and produce whether they are growing in dirt or any other type of medium. Although much of the population would not consider the process of growing a plant in anything other than soil as gardening, today’s innovative growers would certainly disagree. In fact, soilless gardening, commonly referred to as hydroponics, is a growing method that has been not only proven to be effective, it has also been around for thousands of years. 

Generally speaking, growers who prefer soilless mediums know that the key to their success is using the best organic nutrients for soilless gardening. One of the most essential components in a plant’s growing process and overall health is the ‘food’ supplied to its root system. Organic nutrients play a vital part in cultivating healthy plants, especially when a soilless medium is being used. 

What is Soilless Gardening?

For many people, the term gardening generally involves the process of planting a seed or plant in the dirt found in their backyard or the bags of soil purchased at a local garden center—but did you know that most plants don’t require soil to survive? In fact, many plants can grow in water, as well as a variety of other mediums which consist of both organic and inorganic ingredients.

Soilless gardening is exactly what the name implies—gardening without soil. Unlike traditional gardening where plants benefit from the nutrients found in soil, this method involves supplying all the essential soilless growing nutrients into the plant’s water supply rather than through the soil. 

For successful growing, experimentation with variations of mediums is necessary, as it allows a grower to create a positive environment specific to an individual type of seed or plant. For example, a mum plant requires rapid drainage so a medium combination that is bark-based works well because of its high-porosity properties. A lilac plant, on the other hand, requires the nourishment of an alkaline environment so it will need a combination that includes peat moss and limestone to increase alkalinity.

The ideal soilless mix should always offer high porosity and sufficient water retention, as well as provide adequate aeration.

  • Peat Moss - Peat moss is an ideal medium because of its physical and chemical properties. It is lightweight, can hold 15-20 times its weight in water, provides ample pore space, possesses an acid PH level, and can hold nutrients well. It is considered an excellent medium for germinating seeds.
  • Coir - Known for its exceptional ability to absorb and retain moisture, Coir is a lightweight organic material made from the fibers of a coconut hull. 
  • Bark - Any type of bark, similar to Pine or Cedar shavings are a favorable mix for mature plants. Bark shavings are generally added to mixes because of its ability to improve drainage and airspace within the mix.
  • Perlite - One of the more common ingredients in soilless mixes, Perlite is expanded volcanic rock that produces extremely lightweight white particles that hold air well and provide excellent drainage. 
  • Vermiculite - Often used as a substitute for Perlite, Vermiculite is a mica-like material that is heated up and expanded to increase its water and air-holding capacity. It retains nutrients well and is favorable for germinating seeds.
  • Coarse Sand - Also known as ‘builder’s sand,’ coarse sand is always preferred over fine sand because it can easily add weight to other mediums as it improves drainage and aeration.

Soilless gardening has become a popular method for growing because it is considered a cleaner, more sterile environment for plants to grow—unlike dirt or other store-bought soils which tend to be compromised by harmful bacteria and fungi. Gardening without soil also greatly diminishes the likelihood of plants being bothered by garden pests.

Gardening without soil is also popular among those organic farmers who would prefer to ‘keep their hands’ clean while they experiment with innovative methods for growing living things literally anywhere—without being elbows deep in the traditional soil.  

Why are Nutrients Important for Soilless Gardening?

Just like plants that are grown in macro and micro-nutrient enriched soil, organic nutrients for soilless gardening are essential to the life of a plant whether you are growing vegetables and herbs, or cultivating cannabis. All plants need water, nutrients, light, and air to grow and thrive. Equally important, they require support for their roots. Unlike traditional gardening where roots get their support from the soil, soilless gardening provides structural root support with water, balanced nutrients, and oxygen. 

The proper balance of soilless growing nutrients will be key to using this method no matter which medium you choose for your gardening. 

Matching the Organic Nutrients Mix to Plant Needs 

While you can certainly purchase many of the liquid or dry soilless growing nutrients available online or at your neighborhood garden center/nursery, you’ll most likely have to enhance commercial brands with additional nutrients that will meet your plants’ needs. Of course, if you want to formulate a solution with the ideal nutrients to ‘match’ your growing conditions (water retention, drainage system, etc.), you can also create your own soilless mix of organic nutrients. 

According to Cornell University Extension, the ideal soilless medium consists of a basic mix of peat moss and vermiculite or perlite in a 1:1 ratio. However, because soilless mixes possess only trace amounts of natural fertility, you’ll also need to incorporate lime, bone meal, and other nutrients in order to supply your plant(s) with all its nutritional needs.

In general, plants require Nitrogen, Phosphorus, and Potassium (N-P-K). Many plants will also require the presence of secondary nutrients such as Calcium, Magnesium, Sulfur, and Iron; along with very small amounts of various micronutrients. 

The importance of pH in your soilless medium

The soilless growing nutrients you use will also be dependent on your medium’s pH level. Although many plants generally can thrive growing in a medium that has a pH level of 5.5 to 6.5, some plants will need more to adequately supply them with the proper nutrition.

That being said, it will be important to know the pH levels of the mediums you choose to grow your plants in. For instance, peat moss is acidic with a pH of 3.5 to 4.5; whereas vermiculite has a pH of 6.5 to 7.2 and perlite has a pH of 7.0 to 7.5. Knowing your medium’s pH will be essential in determining the additional nutrients you need to add to your mix. In most instances, a soil test kit can be quite useful when you want to accurately access the fertility of your medium so you can adjust the mixture prior to planting. 

Mixing Organic Nutrients

If you decide to use a commercial nutrient solution for your gardening, your soilless mix nutrients should always be diluted to the concentration recommended by the manufacturer. Whether you are using a dry or liquid concentrate, diluting it with water between 65F and 75F degrees is optimal for a plant’s nutrition. However, distilled water is preferred for dilution, as tap water has the potential to contain notable amounts of chlorine, which can adversely affect the growth of a plant.

Mixing the proper amount of nutrient solution will depend on a few factors such as the type of system you are using, the temperature, available light, and the type of plants you are growing.

According to a soil media research study, optimal plant production will be dependent on specific attention to finding the right balance between the proper nutrients and the soilless medium. Finding this balance will help in maintaining a plant’s nutrient supply. Having a clear understanding of how the organic nutrients ‘work’ in a mix will make choosing the right products for your soilless gardening an easy one.

It is important to note that whether you purchase your organic nutrients or mix them on your own, the only way to truly determine/measure the quality of your mix will be how well it performs with your seedlings or plants. Therefore, you should expect to (and, be prepared to) make adjustments—which will generally start with altering the pH levels of your mix. 

If your goal is to learn the best way to apply nutrients to soilless mix, you can find numerous fertilizer ‘recipes’ online for preparing organic mixes to suit your individual gardening needs. Once you have created your mix, how you administer it and for how long should be considered prior to the growing process. Do you want to apply a ‘starter’ mix that will meet the plant’s nutritional requirements for a few weeks? Or use a slow-release mixture that provides a constant supply of nutrients lasting a few months? 

Certainly, for a gardening novice it can seem a bit confusing, but with an improvement in labeling, many commercially sold soilless growing nutrients now have all the ingredients, additives, and other important information clearly listed on the bag or package. 

The Gardening and Plant Care Review Board at the Spruce agrees that making your own mix comprised of all the organic nutrients for soilless gardening you need is always preferable, especially if you want to create a unique blend or are going to be using a larger quantity. 

Here is a popular mix recommended by the Spruce:

Soilless Potting Mix

  • 4 to 6 parts sphagnum peat moss or coir
  • 1 part perlite
  • 1 part vermiculite

Mix with Compost

  • 2 parts compost
  • 2 to 4 parts sphagnum peat moss or coir
  • 1 part perlite
  • 1 part vermiculite

Mix with the Addition of Nutrients

  • Add ½ cup each per every 8 gallons of the mix:
  • ½ cup bone meal (for added phosphorus)
  • ½ cup dolomitic limestone (raises soil pH and provides calcium and magnesium)
  • ½ cup blood meal, soybean meal, or dried kelp powder (for added nitrogen)

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