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03 January, 2023

Self-watering Seed Raisers

I first started making these about fifteen years ago, because everywhere I've lived has been warm to hot, and the ground just didn't hold enough water for seeds to get a start, no matter how much I soaked it. 

Sound familiar? Or are you, like myself, not too happy to have to be watering seed trays up to four times a day? And I'm not even kidding. Fifteen years ago the problem was temperatures in the mid to high 30s and low 40s, (yes degrees Celsius) sand only soil, hot breezes, and never enough cool space, never enough time to be home several times a day to keep the sand damp. 

Also, it was hot. Did I mention it was hot? I occasionally bought a soft drink or soda to make the weather more bearable, and generally got it in 2, 2.5, or 3 litre bottles - because I couldn't see the point of buying nine 325ml bottles just for convenience's sake. (And producing that much waste!!!) But whenever I finished a bottle, I couldn't bring myself to put it in the waste stream just yet. . .

So I made self-watering planters out of them. (It also gave me a good excuse to buy a few more bottles that first summer. . .) And just recently, I've noticed that soda water helps my now fifteen years older body stay better hydrated than plain water, and so I've once again collected a few 2l bottles. 

I've also just had some specialty seeds shipped to me by an online friends in Queensland, and their business is all manner of native, specialty, and herbal seeds. Check their page at FairDinkum Seeds or on Facebook because I assure you that Leigh and Manami are always great value. I've been using their seed farm for years now, and have never once had inviable seeds.

Anything smaller than a 2l bottle is probably not going to be too successful. But feel free to experiment. Bottles seem stable when first filled with soil and water, but the water does evaporate / transpire and when it does, the whole thing becomes top-heavy and easy to tip over. Have it in a secure spot, or, like I did for these six, put them in a seedling tray or similar. We have cats so I've also used plastic clothes pegs to clip all six together. You could also (if using duct tape like I have this time) do a run of tape around all your bottles and that should keep them upright and safe.

Six finished planters, and the raw stock, a 2litre soda bottle.

From the above pics you can probably already work out what's what, but I'll see if I can't make and add a video too. Oh and here it is! On Peertube, Youtube, or Odysee.

Basically you cut the bottle in half in such a way that when you turn the top half upside down and put it back into the bottom half, there's between 10 and 30mm space between the neck and the bottom of the bottle, and then you fix it in place. I've used glue, superglue, and in this case, plastic duct tape. As long as it's waterproof and holds the two halves together in their new configuration. 

Then cut a 150mm long and ~20-30mm wide strip of material, old tee shirt cotton's ideal, and push that most of the way through the neck of the bottle and down into the base of the bottle. You can slightly adjust how damp the soil will be - if you leave the last 50mm just laying in the neck, then only a small amount of soil will get water and so the soil will be drier, if you hold 50mm - 70mm upright while dropping soil in, there's greater contact between the soil and the material and more water will wick up and the soil will be wetter. (Corollary: If more water wicks up, you'll be filling this setup more often, and stand a chance of damping off your seeds with too much water.))

In this case I used an old terry-towelling tea
towel and 
the strips were around 250mm long.

One other important thing to do is to put a hole (not a slit as they block up or self seal) at the highest point that you want the water to go to. I usually pick a point that'll be level with where the neck starts to flare out, that way water won't flood and damp off the seeds/seedlings. I've used a drill and a hot soldering iron but if you've got the utility knife out just push a triangular hole about 2mm - 5mm on a side, and maybe even make two, on opposite sides, just to be sure. 

Fill with layers of potting mix and seed raising mix, or mix your own. I generally use half potting mix and garden soil that's been collected during bed restoration and reclaiming potting soil, then add seeds and cover them with fine peat moss. (I have large-ish drums where I put old 'spent' soil and add clippings and compost and leftover fine mulch and peat and manure and can leave it to rebuild for a year, sort of like in-soil composting. You probably already have a favourite seed raising mix, or will find your favourite as you go.)

Now carefully keep adding water to the seed raiser (which is what this technically is, I guess - although I've also used these to grow herbs on the kitchen window sill) until you get some weeping out of an overflow hole, and let it sit overnight to check how moist the soil gets, if necessary remove some soil and adjust the strip of material up or down. Once you have it behaving right, plant some seeds, and enjoy not having to water it all the time. 

One other thing I love about this system is that because you can leave it a while (sometimes almost two weeks) before needing to top up, this means you won't risk dislodging seeds with watering, so they get a great start. And when you do refill it, do so gently, near an edge away from seeds and seedlings so as not to dislodge them, or very slowly with a very small and fine rose on your watering can.


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