Window Farm: Extra Info

Last weekend, we ran a joint DIY / Bioscience workshop on building a “window farm”. For attendees looking for more information and a place to discuss your ideas, and for interested folk who didn’t get to the workshop, here is where we started. The Windowfarms™ design is open source, meaning the more people who share their ideas and experiences, the better it gets, so please consider joining their forum.

And now that you’ve got the basic know-how, it’s up to you to try things out. Try different plants, different nutrients, different light levels, different designs… And please also let us know what you did and how it works! Join us here in The Edge’s web community, and remember, knowing what doesn’t work is just as important in science as what does!

Keeping your plants alive

Although plants need light, air and water more than anything else, they also need a few mineral and organic building blocks to stay healthy and keep growing. That means you’ll need to give them some food. We’ve used the Accent™ Solution Vegetative Granulated Hydroponic Nutrient, at the dilution recommended for leafy plants (lettuce, in this case), but any hydroponic supplier (and some nurseries) will be able to recommend something suitable for whatever you’re growing.

An important point to remember: for most plants, keeping the roots in water all the time will cause them to rot, so you won’t need to run the pump all the time. We suggest putting a timer on the pump, and ours seems to work well running for about 6 hours/day, but it will depend on how hot the area is. Also note that plants are used to having day and night; one hydroponic supplier told us plants will do better if you turn off the water overnight.

It’s ideal to use distilled or deionised water for your nutrient solution, because then you have full control over what minerals are in your mix, but if you’re in Brisbane, the water is pretty “soft”, so just boiling off the chlorine or passing it through a filter jug will probably do the job well enough.

The Windowfarms website and hydroponic suppliers can give you information about measuring acidity (pH) and nutrient levels (measured as electrical conductivity, cF).

Changing the solution once a week should be ok, but measuring cF and the like can help you to know when the nutrients are running low. But it’s more likely that a nasty outbreak of green algae will happen before that. To keep algae at bay, it’s a good idea to wash out the reservoir when replacing the nutrient solution.


The State Library has a bunch of books on hydroponics, if you’d like to know more and want a break from your computer screen. You’ll find the catalogue here.

Any hydroponic supplier and some nurseries will be able to give you information about what nutrients, light levels etc. work best for which plants. There’s a very handy guide here.


What else you do is up to you, but here are a few things you might like to think about or try…

Nutrients: what’s in a hydroponic nutrient mix? How much do different plants need, and why don’t they all need the same? Why can’t the plants just live off water? Could you use “compost tea” or worm castings in your window farm? Do plants get jittery if you feed them coffee?

Plants: which plants will grow happily together in one column? How can you get faster growth, more leaves, more fruit, weird shapes? Are there any plants that can’t grow hydroponically? What do you have to do differently to grow plants from seed?

Light: how much sun/shade do different plants need? What’s the difference between a sunny window and outside? If you put a light below a plant, will it grow upside down? Do plants need night time (and if so, why)?

Design: how can you get the window farm to stand/hang in your window (or anywhere else for that matter)? How else could you set it up? How else could you pump the water? What could you use instead of the bottles? What could you use instead of the clay pellets?

And… can you do bonsai in a window farm?

Here are loads more ideas for growing stuff in old bottles, and making it science!

Remember, when you do experiments, you need something to compare your results to – a control. The best thing would be to have at least two columns running – one with conditions you know work and one with the test conditions.

Have fun!

Update 27/3/12

I can now recommend refreshing your nutrient solution more than once a week, as ours has turned green again! But on the positive side, the plants are growing well and taste pretty good too 🙂

An alternative to changing water more often might be to use an extra pump to put bubbles in the water: agitation can annoy algae quite nicely.

Update 02/04/12

The bubbles may have sounded nice, but didn’t stop the algae showing up again. But there is still hope! I consulted the Windowfarms website, and realised the vital clue: the algae is green. Green often means photosynthesis, so if we keep the nutrient reservoir in the dark, we should cut down on the algae.

Meanwhile, I built a second column and played with the pump (airlift) configuration a bit, but this seems to have reduced the reliability, and it looks like half the plants have died. So as well as replacing nutrients and blacking out the reservoir today, I’ll be having another go at tweaking the water pumping setup.

One reply to “Window Farm: Extra Info

  1. caroline

    Hi!, all you need to do to avoid algae development is to paint the reservoir. Put a piece of vertical tape that you will remove after painting which will create a colon to view your level

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