Run-to-Waste vs. Recirculating Hydroponics

For experienced growers, hydroponics is an attractive way to garden. Often, this is due to varied growing methods which allow the benefit of choosing a system that suits the individual crop, budget and space. For hobbyist gardeners, this benefit can be overwhelming. This newsletter is for soil gardeners wanting to dip their toes into hydroponics. We’re going to explain the difference between open and closed hydroponics so you can make an informed choice when it comes to what’s right for you.

Before we begin, understand that both open and closed hydroponic systems are good options and there is no right or wrong method for hydroponic growing.

With that out of the way, hydroponic grow systems fall under two categories. These are open (run-to-waste) and closed hydroponic systems.

Closed hydroponic systems are more popular among our customers because water and nutrients are recycled making it an efficient and cost effective way to grow.

Examples of closed systems include; NFT (Nutrient Film Technique), DFT (Deep Flow Technique), aeroponics and the ebb and flow method.

We’re not going to run through these today but we have gone into detail about different systems on social media – scroll down through our Instagram feed if you’d like more information.

In a closed system, nutrient solution is made up to strength before pH and EC levels are adjusted. This nutrient solution is used either continually (e.g. NFT) or intermittently (e.g. ebb and flow) and must be regularly monitored and topped up to ensure a safe pH and EC level.

Because closed systems require maintenance, they are usually more complicated which can be confusing for those new to hydroponics.

For example, the amount of nutrient your plants are able to uptake will depend on the environment, type of system and stage of growth. Unfortunately, this can be difficult to predict, meaning that certain nutrients can easily build up or deplete. Without proper testing, this could lead to nutrient toxicity or deficiency which could damage your crop.

Another challenge faced by recirculating growers comes from water quality. If your water is soft and contains minerals such as sodium or chloride, these could cause problems as they accumulate.

Water high in minerals like magnesium and calcium is known as ‘hard’ water and can also cause serious issues and even toxicity.

In both of these cases, the grower has usually used tap water from a municipal supply.

You can read more about how to test for and fix ‘hard’ or ‘soft’ water on our website under ‘latest news’ (we have linked to this article below).

In a run-to-waste system, nutrients are not reused and usually drain from the base of the grow medium. This excess nutrient solution is often referred to as “run-off”. Open hydroponic systems are much easier to maintain and run because of this.

The volume of run-off produced in an open system should be between 10 – 30% of the solution initially applied to crops.

Aside from being easier to manage, run to waste systems are advantageous because at each irrigation your plant’s root zone receives a fresh, balanced supply of nutrient.

Although this method may seem wasteful, most growers collect nutrient run-off to be used in other ways such as on lawns, trees, potted plants and ornamentals.

It’s worth noting that in some countries nutrient discharge is outlawed or heavily regulated. Check with your local government before setting up an open hydroponic system.

At Aquaponics WA and Hydroponic Xpress, we are always looking for ways to improve our content. If you’re interested in hydroponic or aquaponic gardening, we would love to know what you think about our newsletters and what you would like to see from us in the future. Send us an email at marketing.aquaponics@iinet.net.au if you have any feedback to share!

Hopefully, this newsletter has helped you to understand the difference between open and closed hydroponics and, as always, happy growing!