$34.99 for an 18-inch round. $27.99 for a 24-inch box. I stood in the aisle with both in the cart for a good ten minutes, doing porch math and feeling vaguely guilty, before I bought them to settle an argument I've been having with myself for three summers: are self-watering planters worth it on a porch as hot as ours?
Why our porch makes a good test
Our porch faces southwest and gets sun from late morning until it drops behind the houses across the street. By July the bench end sits in the 90s most afternoons, and the galvanized can sweats in my hand before I've filled it. Last summer I hand-watered 34 containers plus the raised beds, and that's a big part of why our summer water bill hit $214. This year there are 38 containers between the porch and the yard, and the ones on the sunny end need water every single day in July, the small terra cotta ones twice.
Terra cotta breathes. That's why rosemary and thyme like it and why I love how it looks, softening from orange to chalky salmon as it ages. But it pulls water out of the soil through its walls, and on a hot porch that turns basil and petunias into a daily rescue job.
How I set it up
A self-watering planter has a reservoir in the bottom, a wicking area where the soil drinks from it, a fill tube, and an overflow hole so a week of rain can't drown the roots. The idea is that plants pull water as they need it, and I refill the reservoir every few days instead of watering from the top every day.
I planted both last Sunday and matched each one with a plain container I already own, so I'd be comparing like with like:
- 18-inch self-watering round against an old 18-inch terra cotta pot, each planted with one red geranium, two purple petunias and trailing white bacopa.
- 24-inch self-watering box against a 24-inch galvanized trough, each with three Genovese basil plants from the same seed tray.
Same Pro-Mix, same small scoop of Garden-tone, and all four sit side by side at the sunny end of the bench. The instructions say to water from the top for the first few days, until the roots reach down into the wicking zone, so that's what I did. The log started that Sunday. My can holds a little over two gallons, and I've painted quart lines on the inside with an old bottle of my nail polish, so every pour gets measured and goes into the notebook.
Early notes, six days in
It's early, and the weather has been kind: mostly 70s, with one 84-degree afternoon on Thursday. Even so, there's a pattern starting.
Water. The terra cotta pot needed water five of the six days, about nine quarts total. The galvanized trough needed it five of six days too, about eight quarts. The two self-watering planters got their top-watering for the first few days, and then one reservoir fill each on Thursday, and together they used about six quarts. Less water, and far less often. The "less often" matters more to me than the quarts.
Growth. No difference worth writing down yet. The basil in both containers is the same height, and the petunias look equally pleased with themselves. Ask me again in July.
Cost. The two planters came to $63 out of this year's $500 garden budget, and the plain pots were already mine. The water these save will never pay back $63. A few quarts a day is pennies. If they're worth it, it'll be because they let me skip a watering on a 92-degree day without coming home to a crisp geranium.
Looks. To my painter's eye the self-watering round looks like a patio-store pot, because it is one. It's a flat putty color next to the warm, weathered terra cotta. I'm already plotting how to hide it behind the bacopa.
A four-day intermission
On Monday Kevin starts rebuilding the rotted southwest corner of the porch, which happens to be the sunny end where this whole test lives. So tomorrow afternoon Nate and I move everything off that end: the tomato buckets, the nine fabric pepper pots, the herb pots on the bench and all four test containers. For four days they'll sit at the shady end of the porch, and the log will get an asterisk. Not exactly lab conditions, but the planters will be back in the sun by Friday, and the real test is July anyway.
