Passive Hydroponics Part 1: Lettuce | indoorsalad
ginger's picture

Passive Hydroponics Part 1: Lettuce

9 week splasher and coirstone lettuce, other lettuce splashers behind I just completed an experiment on passive hydroponic lettuce. No pumps, no splashing – just pour nutes into the reservoir, and let them grow. I mentioned this possibility in my book, but hadn't run the experiments.

It worked great. Less effort than splashers, and grew lettuce just as well.

I created the IndoorSalad Lettuce Splasher product as a sort of launch special for my book. It's an inexpensive kit to grow lettuce with hand-aerated hydroponics. These work great for me, and have taken over the lettuce growing, freeing my pricier Aerogarden capacity for more demanding crops like eggplant and tomatoes. I used to devote up to three Aerogardens at a time to greens. No more.

But the splashers haven't sold well. Of course, I could market them better. angel  But they take attention, manually splashing once or twice a day to aerate the roots. For me, growing up to eight of these things at a time – the splashing gets to be a chore.

The point of all that splashing is to get air into the water. But roots aren't meant to be submerged in water, anyway – they drown. For my passive system, what I did instead was mix equal parts of the splasher growstones with coco coir. Coco coir is just coconut husk fiber. It's inert, has no nutritional value, but it wicks up liquid, and doesn't compact. Air stays in the fibers, and in the growstones.

I expected getting the right balance of coir to stones to be tricky. It wasn't – roughly half and half worked fine. I expected wicking upward to be tricky. It wasn't. I just used two nested tubs – of the same size, not a smaller inner one – with holes in the bottom of the inside tub. Filled the inner tub with my coir-stone mixture. Put hydroponic nutrient solution in the bottom, liquid reaching about an inch or two up into the coirstone. And other than that, grew my lettuce just as with a splasher.

It worked a treat.

The coirstone system still needs watering every few days when the plants get bigger. But if your lifestyle weren't compatible with even that level of attention, you could simply grow fewer lettuce plants, or use bigger tubs, to bring maintenance down to once a week.

The coirstone system is less reusable than splashers. You can't readily wash and reuse the coirstone mixture for your next lettuce crop. Best to just throw it out and start fresh. I find my guilt level on this quite bearable, though. Coir is a renewable resource, the growstones are made from recycled bottles, and I never liked washing the rocks, anyway.

Tune in next time for a report on the more challenging half of this experiment – dwarf tomato plants. Now that I couldn't do with the splashers. But I'm harvesting first fruits now!

Sign up for the mailing list (top right of page), or become a member of, to get notified of new blog posts, products, etc.

Indoor Salad: the Sequel

Not much feedback yet on last week's question – what short sequels people might be interested in. Topics that people expressed interest in:

  • Hydroponic nutes, more in-depth info.

  • Growing veggies in Aerogardens.

  • Growing indoor/outdoors – great yields from tiny spaces and short seasons.

Still plenty of time to chime in! Any input appreciated.

What's Growing Now?

Still harvesting lettuce, stir-fry brassicas, and cucumbers. My eggplant died mysteriously, but I enjoyed a nice little crop first. Now harvesting tomatoes from five plants. My latest baby veggie plants are my first green onions, white onions, and a fractal broccoli. Wish me luck!

What are you growing now?