I dumped salt in my compost pile - how bad is it?

July 21, 2021 5:31 PM

Without thinking, I dumped the salty ice from an ice cream maker on my compost pile. Total is probably 1.5 c. rock salt. Do I have to worry about using the resulting compost next year?
posted by Emmy Rae to Home & Garden (5 answers total)

No. We mix our fertilizer with salt, per its instructions. It’s fine.
posted by slateyness at 5:35 PM on July 21, 2021 [5 favorites]

No worries. Run a hose on it for a bit to disperse it if you want, but by the time you use it snow will have fallen on it and all kinds of other decomposition will occur and it will be fine. Also keep adding other things to the compost.
posted by A Terrible Llama at 6:54 PM on July 21, 2021 [1 favorite]

Good job! One of the ways, in a lab setting, to encourage lactic acid bacteria (which will outcompete, say, coliforms) is to crank up the salt to 5% wt/vol. So your 1.5 cups is but a pinch. LABs are naturally abundant on grasses, which is why silage works, and key to all the good lacto-ferments. People finger-wag me I shouldn't pee on the compost heap - because salt. Now I can say at least I didn't brine the microbes.
posted by BobTheScientist at 7:35 AM on July 22, 2021 [1 favorite]

Best answer: So I assume you are worried about the salt from the compost affecting your plants next year?

1.5 cups of rock salt is about 700 grams. saline soil has upwards of 3 grams per liter of salt. For this salt to make your soil saline, you'd need to distribute it over at most 250 liters (9 cubic feet) of soil area. Unless you are planning on using all your compost on a 3'x3'x1' raised bed with no drainage, you're good to go.

(incidentally, water flushes out salt from soils very effectively, so unless you irrigate heavily with no runoff and poor drainage, you're unlikely to face increasing soil salinity over time. This is why soil salinity is mainly a problem in arid regions.)
posted by goingonit at 11:40 AM on July 22, 2021 [2 favorites]

Best answer: If you really feel you need to do something, add some gypsum to replace sodium molecules clinging to soil particles with calcium. The sodium can then be leached more easily by flushing with water. Whatever amount of salt you used, just add that much gypsum to the compost pile.

This is the remedy for sodic soils- if you have saline soils due to other types of salts, such as fertilizer salts, the remedy is just flushing with water. Compost can often be high in salts anyway so quite honestly you probably have nothing to worry about. That said gypsum is usually a very good thing to add to soil generally.
posted by oneirodynia at 1:08 PM on July 22, 2021 [1 favorite]