How much space do I need between hydroponic net cups?

Plants often have a recommended spacing when growing in soil, and I was curious if they had to same requirements when growing hydroponically. I’d like to grow several plants at once, maximising the shelf space that I have.

It would be great to have several lettuce growing in one container. I plan to harvest the larger leaves as they become available, leaving the plant to continue growing, rather than harvest the entire plant in one session.

Why Plants Need To Be Spaced

If lettuce are grown too close to each other

they will likely receive less than the required amount of light… they can also receive less air/CO2 than they require for proper growth.

We Grow Hydro

It seems that adequate airflow is also required to help reduce mildew and other diseases. And plants need to meet a certain level of light in order to grow; I learnt this the hard way in the post Do I Need Grow Lights?

What Spacing Is Ideal

There doesn’t seem to be a consensus of how close net cups can be before lettuce growth becomes detrimental; measured centre to centre of each cup. Part of the problem lies in what plant is being grown, as well as when and how often it is harvested. For example a larger plant (like a tomato) will definitely need more space to grow than a smaller plant (like a lettuce). Secondly, many assume you would harvest an entire mature plant in one session (such as commercial growers), whereas some people prefer continual harvesting where they only take a few outer leaves at a time and let the plant continue growing.

WeGrowHydro claim that plants should be spaced a minimum of 18″ apart (45cm) for plants less than 3 feet in height! For me that’s a total of 1 plant per shelf! If they had to point out plants less than 3ft, it makes me wonder if the plants they are growing are much larger than lettuce…

SFGate Home Guides suggests that spacing should be 8-12″ (20-30cm).

Bernard Kratky himself, the founder of the Kratky hydroponic method, wrote in a paper:

“Two common planting densities for lettuce are 1.5 and 1.9 plants per square foot”.

Bernard Kratky

That calculates to one lettuce every 6-8″ (12-20cm) for commercial growth. Again, this assumes that the entire plant is harvested in one session.

Steemit claims that lettuce should be at least 6 to 8″ (12-20cm) apart. However their article looks like it’s written for commercial growers – or large setups where you might harvest entire lettuce in one session.

Photos on Steemit Website - Their Greenhouse
Photos on Steemit Website – Their Greenhouse

Christian Haschek‘s blog shows a vertical hydroponic setup where he spaces the cups by 4″ (10cm). This is the first case I have found where the hydroponic setup is aimed towards home-growers rather than commercial, so it could be assumed that he harvested individual leaves or perhaps before the plants became fully mature.

Christain Haschek's Vertical Hydro Setup
Christain Haschek’s Vertical Hydro Setup

Even my Aerogarden Bounty has spacing of only 4″ (10cm) between each pot. This system is definitely aimed at the home grower, encouraging continual harvesting of the plants.

What Spacing Do You Use?

I’m curious to know what spacing you used? Please share with us what plants you have grown and what spacing you used between net pots (centre to centre).

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