Evidence that self-watering containers are GREAT

While planning the new growing season, I think back to learning from last year, and what might be useful to you if you are growing in containers. My most successful experiment in 2010 was the self-watering containers. The marrow below was grown in one and is included here as (unscientific) evidence in their favour – imagine  a marrow like this from a conventional container! The yields of runner beans (5kg from one 60cm x 60cm self watering container) and tomatoes (about 8kg from each 75cm x 35 cm self watering container) were good, too.

Evidence for self watering containers!

Why they work

Self watering containers work so well because:

  1. On a hot day a growing tomato plant will consume a gallon of water. It’s hard to provide this much water in a conventional container (unless you water 2 or 3 times), but easy with a large water reservoir. So your plants get the water they need to grow to their full potential.
  2. Veg crops like runner beans get stressed by fluctuating water levels between waterings in a conventional container. A water reservoir removes this stress.
  3. Water reservoirs encourage roots to grow down towards the water and for a strong root system to develop.

What to grow in them

You’ll get the most benefit from growing water hungry crops in self watering containers like tomatoes, courgettes, squash and runner beans.

Home made or commercial product?

I experimented with home made self watering containers and a commercially made ‘Earthbox’ in 2010 (both holding the same volume of soil). Both yielded similarly well (in an unscientific experiment). You can see them growing (rather untidy) tomatoes in the picture below. I also added some simple reservoirs to conventional containers, which I blogged about here.

Earthbox on the left, wooden home-made on the right

You’ll find a plethora of instructions on how to make self watering containers on the web. The design I use most is described on page 36 of this excellent PDF from the Rooftop Garden Project in Montreal.  I also adapted this design for my wooden containers – using plastic boxes for the reservoir, and then an estate agent sign to separate the soil from the reservoir. Here it is under construction:-

Inner workings of home made self watering container made from estate agent sign, pvc pipe, old floor boards and a plastic container for the reservoir

Earthbox or home made, the choice is not an easy one. The Earthbox costs £35 and is quick and easy to set up.  My home made self watering containers cost less than £5  each but took a whole day to make each one.

Which you go for depends on your time, DIY skills, tools etc – and also what sort of shape and size you want. If you want big boxes to fill a particular space, then home made wooden containers are perfect.  Equally, if you want to do it on a budget, home made is also best. However, for window sills, I like the Earthbox. It has a good capacity, and is ideal for growing vegetables (most other commercial self watering containers are designed more for flowers). It is also strong and light – which makes it easier than a wooden box to move (although it is still very heavy when full). The Earthbox also comes with casters – good if you have patio where you can move it around (But I have no use for casters and find it a bit annoying that they come bundled with the product).

True, Earthboxes are not a low cost solution, but I reckon they represent a good investment. They are strong, well designed and should last many years. On a sunny window sill you can grow £40 – £50 of tomatoes in one box, so it can pay for itself in a season. (NB I should maybe mention that I am not affiliated to Earthbox in any way!).

9 comments… add one

  • I have been using self-watering pots and attempting to make them for years, but it suddenly occured to me – what is the difference between using a pot with a reservoir and standing a pot in a saucer of water? People say that if plants ‘sit’ in water they get waterlogged, but I can’t see how this is different to them ‘wicking’ water up from a reservoir. What am I missing.?

    Reply
    • Great question, Kate. In a container with a reservoir, if it is designed correctly, only a portion (around 5% – 15%) of the soil will usually be in contact with the water. If too much of the soil is in contact with water, it becomes waterlogged. Standing a plant in a tray of water is fine for a few hours (and can be a useful technique on hot days), but if it is sitting in the tray for long periods it will indeed get waterlogged as you say. Does that answer your q?

      Reply
      • Thank you! I had suspected as much, but could not find anywhere that actually said so, so it is great to have your answer! I think in that case that the simplest self-watering set-up would be to put a wick through the drainage holes into a drip saucer (or other reservoir) and suspend the pot above it, by, for example, sitting it on pot feet. I shall try it and let you know if it works!

        Thank again for such a quick and helpful response.

        Reply
        • Hadn’t thought about this – have you had a chance to give it a go yet?

          I really like the recycling box design, and I’ve come across it at an opportune time; the city council have just decided to swap our street over to wheelie bins and we have two big boxes waiting to be re-used.

          I know the design would be great for big hungry tomatoes, squash, etc. but a more rudimentary wick system would be fun to try out on smaller containers (salad greens, herbs), which I currently have sitting in plastic tray saucers. I put stones in the bottom of my pots to keep the soil from becoming waterlogged, but I now spend too much time picking small stones from my re-used compost/worm bin! Surely there’s a more elegant solution

          Reply
  • Impressive results, for sure! I have just acquired some self-watering plastic planters made by Stewarts which will probably be good though I have not had the chance to try them yet. Another little trick I use is to stand my pots in huge saucers, and fill the saucer with water first thing in the morning. The water gets used up during the day while I’m out at work, but at least it helps to stop the pots drying out.

    Reply
    • The best self watering containers I’ve found in the shops are Earthboxes – but the Stewart ones are not bad, if a little smaller (so not quite so good for hungry crops like vine tomatoes or courgettes). The saucer trick can be a handy one – you just need to take care that the plants don’t sit in the water for too long or else the soil in the pot can sometimes get water logged – but a few hours a day is probably OK (and much better than a pot drying out!).

      Reply
  • That’s really impressive. I wish my DiY skills were up to scratch (or even that I had some)

    Reply
  • That is an amazing harvest! I must find out more about self watering containers for this summer

    Reply

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