Soilless Agriculture: An In-Depth Overview

Soilless Agriculture: An In-Depth Overview

Adam French

February 11, 2019

Everything you need to know about soilless agriculture

Agriculture without soil? It sounds like another hipster trend that pops up in places like Berkeley and San Francisco. In reality, soilless agriculture is an agricultural method that enables a stable and sustainable food supply. It allows us to run high-yield grow operations in completely controlled indoor environments. So, why does that matter? Well, there are a few very important reasons that may enlighten you to the real potential in soilless agriculture.

  • No need to use pesticides (less poison sprinkled on plants means healthier food and less cost).

  • Extreme decrease in water use (you need 90% less than soil-based methods).

  • Flexibility in use (use it indoors or outdoors, and if indoors you can grow whatever you want, wherever you want, whenever).

Now, I want to focus on the flexibility of soilless agriculture and why this is so important in today’s world. As you know, people around the world are getting used to buying whatever kinds of produce they want — even if it’s not in season. This means importing a lot of produce from other countries. That’s a decent solution, but it has many side effects. First, it costs more money to buy food and have it shipped to your country than just growing it locally (you’re outsourcing taxable labor and covering transportation costs). Second, the emissions from whatever vehicles that are shipping the produce pollute the earth and bring us closer to climate catastrophe. Third, if a natural disaster occurs in the other country, you can’t import food from there for a while. If your country heavily depends on the damaged country for food, you may have a nationwide food shortage. Just think about what would happen to the world’s wheat supply if a disaster occured in North America. In summary, the extreme interconnectedness of the global food system creates an unsustainable and potentially unstable situation. Soilless agriculture helps to address this issue because it’s a perfect method for localizing agriculture and bringing food production closer to the consumer. This localization of food production stabilizes the food system and improves the freshness of the food.

Since we know the benefits of soilless agriculture, how did it come about? I thought it was invented by a Silicon Valley genius in midst of the current technological explosion, but it’s roots go much deeper than that. Primitive examples of soilless techniques were discovered at the Floating Gardens in China and the Hanging Gardens of Babylon! Ancient wisdom at work. <Image of either Chinese or hanging gardens>

Although soilless agriculture has been utilized throughout human history, the modern introduction to the technology was lead by William Frederick Gericke when he grew 25 foot high tomato vines without soil, using a nutrient rich water solution. This grand achievement drove more and more research to the technology, and its advantages were discovered on a mainstream level.

So, how do you actually implement hydroponics? Let’s start with the definition. According to Google, hydroponics is “the process of growing plants in sand, gravel, or liquid, with added nutrients but without soil.”. So basically hydroponics is the sciency way of saying soilless agriculture. Simple, right? Well… not so much when you get into the implementation details.

There are quite a few ways to implement hydroponics. The simplest way is to put a plant in a pot with a growing medium — a substance that doesn’t supply nutrients to the plants but supports the roots — and hand water it with a solution infused with the needed nutrients. This is the essence of soilless agriculture. All the plant needs is oxygen, a variety of nutrients, light, and it will grow. No need for soil or the constraints that come with it. While this may seem simple, getting an optimal yield requires knowing the intricacies of plant growth and applying this knowledge to each aspect of the hydroponic environment. For clarity, I’ll break down the different complexities associated with each part of hydroponic growth: The SolutionThe Growing MediumThe Lighting, and The System.

The Solution

The solution is the lifeblood of your hydroponic system. The yield, health, and resilience of the crops you grow depends on a well-crafted solution. Sometimes it’s difficult to create a perfect solution, however, because the exact amount of specific nutrients in the solution depends on the plant you’re growing.

What are the steps to creating a balanced and fruitful solution for your system? It all starts with the water. Whether you’re using tap, filtered, or water from rain buckets (not recommended — I would filter it first) you should get a laboratory analysis of your water. In this analysis, pay close attention to the alkalinity of your base water — it will give you a good indication of how to devise your fertilizer strategy. If you have high alkalinity, the pH of your end solution will tend to be higher. The pH of your solution is one of the key factors in determining the health of your plants, and you want to keep it in the range of 5.5 to 6.5 for most plants.

After you have your water source figured out, you need to gather all the needed nutrients. The types of nutrients in your solution are primary and secondary nutrients (nutrients that plants need a lot of) and micronutrients (trace amounts of specific materials).

The primary nutrients are Potassium, Nitrogen, and Phosphorus. Without the a healthy dosage of these, your plants won’t grow correctly and will be more susceptible to disease. The role of each nutrient is as follows:

  • Nitrogen (N): Assists in protein manufacture, promotes plant strength, and makes use of the plant’s carbohydrates.

  • Phosphorus(P): Facilitates photosynthesis, controls cell division, and regulates use of sugars within the plant.

  • Potassium(K): Enforces disease resistance, helps metabolize nutrients, and regulates water usage.

Each primary nutrient plays an essential role in the health and yield of the plants, so make sure there is a balance of each one in your solution.

Secondary nutrients include Calcium, Magnesium, and Sulfur. These nutrients are needed in only moderate volume by plants, but are also essential for healthy growth. They play the following roles:

  • Calcium(Ca): Regulates internal pH, facilitates disease resistance, fuels cell division and cell wall formation.

  • Magnesium(Mg): Assists internal oil, sugar, and fat formation, boosts photosynthesis.

  • Sulfur(S): Assists seed production, adds flavor, is building block for proteins and amino acids.

Micronutrients are a bit different from primary and secondary nutrients in that they’re optional and applied in trace amounts. Usually you would only add extra micronutrients if your plants were showing signs of deficiency (discoloration, hollow fruits, limited growth, etc). There are quite a few micronutrients but the main players you’ll want to know about are zinc, copper, iron, manganese, chlorine, molybdenum, and boron. The cool thing with micronutrients is that they can boost absorption of other nutrients.

For the ongoing maintenance and fine-tuning of your solution, the two measurements to pay attention to are pH and electrical conductivity (EC). The pH should fall into the range of 5.5–6.5, and the electrical conductivity should be between 1.5 and 2.5. A high EC rating means your solution is too nutrient dense, so in this case add water until it comes under 2.5. Here’s a great article that gives a step-by-step breakdown on how to make your own solution.

The Growing Medium

Since hydroponics are systems without soil, you may need a static substance to support the roots of the plants. The vast variety of growing mediums and different mixes can overwhelm and confuse so i’ll just talk about the characteristics of different types of mediums and the circumstances in which you want them.

The key characteristics in your growing medium are water retention, aeration, and pH neutrality.

  • Water retention describes how slowly it takes for solution to filter through the medium, and how long it stays available to the plant. Use mediums with high water retention in drip systems, and lower water retention mediums in flood-and-drain type systems.

  • Aeration is an indicator of how much oxygen is getting to the roots of the plant. Roots need oxygen to convert their stored energy into growth, so it’s a super important characteristic. You can increase aeration by making the medium more porous, with cracks and slivers for oxygen to seep through. Aeration to the roots also makes them more effective at uptaking water, so if they don’t have space to breathe, the plant may show signs of water shortage.

  • pH neutrality tells you how the growing medium may affect the pH of a plant’s growing environment. Grow mediums should normally be neutral so they don’t have side effects on the solution or the environment

Common Growing Mediums

Coco Coir (The discarded husks of coconut) protects seedlings from harmful fungi and salt damage, has high water retention, and is biodegradable and cheap. These advantages make it perfect to use in drip or wick hydroponic systems, where water comes little by little. You won’t want to use it in flood systems though — it can have poor aeration if irrigated poorly. It also can draw down some of the calcium in the nutrient solution. To mitigate it’s high water retention, you can mix the fibers with a chunkier medium to create some drainage.

Best Use Case: When you want a cheap and sustainable medium with good water retention.

Expanded Clay Pellets are a great medium to use if you want fast drainage and an infinitely reusable medium. They also don’t affect the solution’s nutrient balance. They also have great aeration, although this can mean a plant’s roots dry out quickly. Another issue with clay pellets is that they’re sourced from strip mines, so the environment may have been harmed in their creation.

Best Use Case: When you’re worried about overwatering or nutrient disruption.

I decided to pair Perlite and Vermeculite together because they’re almost always mixed in use. Perlite is superheated volcanic rock. It’s a lightweight, neutral medium that will sometimes float on water when flooded. A downside of perlite is that it leaches nutrients easily, disrupting the delicate balance of solution. Vermiculite is very similar to perlite, a lightweight mineral that draws nutrients upwards and retains water at a high rate. When combined, these make a soil — like mixture with great oxygen and water retention. One thing you must be careful of is the particles of this mixture that can infiltrate your solution without a great filtration system.

Best Use Case: Same as Coco Coir, but will be a little bit more expensive.

Wood Chips are a simple, cheap (probably free), and organic growing medium. Wood chips are a great way to grow hydroponics, and will leave your environmental conscience clean too! There are a few downsides, as wood chips can degrade over time and aren’t the most reusable medium. It also might not be sterile, and attract pests.

Best Use Case: When you want to save money, and are running an indoor grow operation where pests and diseases won’t be as much of an issue.

Those are some tried-and-true growing mediums that you can use in your systems. When selecting growing mediums, keep in mind the requirements and orientation of your system(see: The System). You need to customize a combination of mediums based on the irrigation methods, types of plants, and environment (inside or outside).

If you want to go into more depth on growing mediums read this articlethis article, and this article.

The Lighting

There are a few different types of lighting for your hydroponic system with their own advantages and disadvantages. In lighting, you want to find the right balance of intensity, spectrum, and cost. The most useful types of lighting for hydroponics are Fluorescents, High intensity Discharge Lamps (HID lamps) and Light Emitting Diodes.

Fluorescents are great for the growers that are just starting out. They’re efficient, widely available, and produce a spectrum of light that is conducive to plant growth. But, they emit weaker intensity light — which makes them sub-optimal for larger plants and grow operations.

One type of fluorescent lamp is the Compact Fluorescent Lamp (CFL). This type of lamp is cheap, easy to install (just screw it in), and efficient. One downside of CFL’s is that they emit light in all directions, so you’ll have to use a reflector to make sure you’re not wasting light and energy.

Another type of fluorescent light is the regular Fluorescent lamp. These are a larger version of the CFL’s and they emit more focused but weaker intensity light — which makes it sub-optimal for larger plants. The advantages are the same as CFL’s, but they might require a little more set-up to get working properly. A disadvantage with these and the CFL’s is the life span. To keep the system working optimally, these lamps should be changed out every year. This increases costs overtime and brings upon the question of disposal, as fluorescent lights contain mercury and other harmful chemicals.

The final type of fluorescent is an induction fluorescent. These have the same advantages (efficiency, spectrum) and disadvantages (intensity) as the other fluorescents with one catch: the lifespan is 10X longer than the previous two lights!

High Intensity Discharge Lights are great for experienced growers with large operations. The frequency of their light closest matches sunlight compared to the other types. The high intensity characteristic makes them the go-to choice for growing large plants indoors. This high intensity also leads to higher heat production, which can be mitigated by putting them in an open space where the heat can dissipate

Metal halide (MH) HID’s emit a bluish light that benefits leafy and vegetative plants while high pressure sodium (HPS) lights emit an orange light that work best for flowering plants and fruits.

Light Emitting Diodes are the newest option out of the three. They are also the most expensive. However, this upfront cost will be paid off in the long run because of their industry leading efficiency (they use around ⅓ the energy of fluorescents) and lifespan. If you don’t have tight upfront budget constraints, I recommend these because of the long-term savings (around $5,000 a year in recouped energy spending). The spectrum is a bit less optimal than fluorescents, but the difference isn’t very significant.

As you can see, the correct lighting setup will be determined by your budget, the plants you’re growing, and the size of your operation. As we look to the future, LED costs will go down and this will drive adoption of them over fluorescents.

The System

Whew, I just went through A LOT of stuff (don’t worry, we’re almost done :) ). Now, let’s put it all together! All the different types of growing mediums, solutions, and lighting setups can be put together in different ways. It all depends on your circumstances, budget, and expertise. Here are all the different types of systems, what they look like, and which situations they work for.

Hand Watering

Use this system if: You are a beginner in hydroponics or growing in general who doesn’t have extra time or money to spend on setting up a complicated hydroponics system with a lot of equipment.

Setup: Mix together your growing medium and nutrient solution, then put the plants/seeds in the medium and start watering!

Best medium: A mix of vermeculite/perlite and coco coir.

Best Practices: Make sure your nutrient solution is stored in a stable place where levels of nutrients wont fluctuate and other living things can’t get into it. Also, remember to water the plants!

Deep Water Culture

Use This system If: You want a relatively simple hydroponic system that is more intricate than hand watering — and you have a small budget to get started.

Setup: As It would be incredibly tedious for me to write words about how to setup this system, a video would do a much better job. So watch this for setup instructions!

Best Medium: Expanded clay pellets, or a similar medium with ph neutrality

Best Practices: Make sure the nutrients in your solution are very accurately measured, as a little mistake can go a long way in this system. Check the ph and electrical conductivity of the solution thoroughly before setup.

Ebb and Flow

Use This system If: You want a lower cost, flexible homemade hydroponics system and want to put the time in to a more complex setup.

Setup: Epic Gardening on youtube does a great job making these hydroponic system setup tutorials. So watch this for setup instructions!

Best Medium: The exact medium depends on how often you want to flood your plants, but a heavier medium like coco coir or expanded clay pellets is highly recommended.

Best Practices: This method requires more attention after setup than the previous two. Make sure you’re flooding the plants at different intervals throughout the year to match the change in light exposure and temperature, as the water will evaporate at different rates. Also, make sure the grow tray (see diagram/setup video) is level so all the plants get the same level of nutrients.

Drip System

Use This system If: You want to grow larger, greedier plants with a simple setup but don’t want to use a lot of water doing it.

Setup: Epic Gardening on youtube does a great job making these hydroponic system setup tutorials. So watch this for setup instructions!

Best Medium: The exact medium depends on how often you want to flood your plants, but a heavier medium like coco coir or expanded clay pellets is highly recommended.

Best Practices: This method requires more attention after setup than the previous two. Make sure you’re flooding the plants at different intervals throughout the year to match the change in light exposure and temperature, as the water will evaporate at different rates. Also, make sure the grow tray (see diagram/setup video) is level so all the plants get the same level of nutrients.

Wick System

Use This system If: You are going to grow a relatively low-water plant (like rosemary or a fast-growing lettuce), and want to build the system quickly and simply.

Setup: Here’s a nice tutorial on wikibooks that explains what materials you need and how to put it all together!

Best Medium: With a wicking system, choose a medium that absorbs and retains water well, like coco coir, perlite, or vermeculite.

Best Practices: Make sure there are multiple wicks when you set this system up so you’re sure the plants get enough water and nutrients. Keep the water levels in the reservoir high and wash growing mediums frequently to prevent nutrient buildup.

Aeroponics

Note: Aeroponics is not hydroponics. It differs because it uses a spray to diffuse the mineral-rich water onto exposed roots instead of a model where the roots are submerged in water or a growing medium.

Use This system If: You’re an experienced with hydroponic or diy projects with hands-on and technical knowledge that’s ready to build a more complex system with some automated parts. Another good reason to use this system is if you need to grow stuff quickly, for commercial sale or to feed your family.

Setup: Check out this video series by Peter Stanley for a step-by-step instruction on how to set up a cheap aeroponics system.

Best Medium: No medium needed!

Best Practices: Since the roots are exposed, aeroponic growing presents a large opportunity for disease and nutrients clogging the root system. Make sure the roots stay clean on a daily basis. Also, the misters tend to clog as well, so keeping them clear of debris with frequent maintenance can mitigate that risk. Just be sure to keep close tabs on the most vulnerable parts of the system.

There you have it! Hopefully all of this knowledge on hydroponics helps you get started with your own growing operation or helps you transition to a new growing method that fits. I enjoyed learning about all the complexity and the advantages of unique technology, and I’m excited to see what advancements may be made in the future! Thanks for reading :)

Adam French

I love learning and writing about programming, agricultural innovation, and design.

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