Where do epsom salts go after a soak?

I saw a podiatrist yesterday for the first time. (I've been limping for about five months and saw my regular doc first after it didn't seem like it was healing.) I apparently have Achiles tendonitis and maybe plantar fasciitis and maybe bursitis -- definitely bone spurs on the xray. Anyway, I don't love much of what the podiatrist is suggesting, though I'm taking his exercises and augmenting them with stuff I'm reading online (including here at Permies where a handy thread just popped up into currency). One of those things is epsom salt soaking my foot and calf. I've never done that, but just ordered some. I assume I'll be able to figure out the concentration from the packaging since I haven't read anything yet that was specific. But what I'm really wondering is what to do with the bath after the soak.

First, is it bad for the septic? That's very much not my first place to put it, but winter is coming and we have pretty real winters here in northern MN.

Assuming I'm going to be adding it to the garden: how? Where? In what concentration? If none of you come back with anything authoritative, I'll just dump it on the various compost piles until they ice over and assume that system will buffer and leach it as needed.

It always ends up in the garden for me.  When I was in MN, it would go on the tomatoes this time of year. Concentration…maybe a couple of tablespoons per gallon of water per plant.  

I just checked several sites on the net. Those sites say 1 tablespoon per gallon.  Martha Stewart was one of the sites.  I pretty clearly remember using two tablespoons , but we had really sandy soil and watered often.

Epsom salts are chemically known as magnesium sulfate MgSO4

Magnesium sulfate is very slightly acidic but it is not meaningful in the grand scheme of a septic system's biome. I would not think twice dumping Epsom salt water down into my septic and actually do this frequently as we do soaks in my household tub from time to time. The added magnesium is reported to possibly be beneficial to bacteria. You would have to dump quite a large amount of straight Epsom salt into your septic to start disrupting it from what I can read.

I'm not sure of concentrations for garden use but I would love to hear other's experiences. I read that there is evidence of grey water systems benefiting plant growth when Epsom salts were discharged but it did not indicate concentration.

Fun fact that I pulled from the internet. Epsom salts start showing antibacterial properties at 2000 grams per liter. If you can keep your concentration under that, you should be golden.

Septic doesn't seem to mind, so long as it's not excessive (instructions say half a cup per bath tub, a few times a week is fine)

Epsom salts are often used to help the garden, especially if you live somewhere with non acidic soil.  I put my waste water at the base of the magnolia as it strengthens the wood.  Hydrangea can get better colour. Some veg also benifit.

If the pasture or hay feild needs magnesium, it's sometimes applied to the soil.

My local farm supply store sells it in the 35kg bags it's so useful on the farm.  But it depends on what your soil is like already and what the specific plants needs are.  

The concentration i use it here for my plants is influenced by the extremely acidity of the soil here, so we use it sparingly unless there is a specific problem we want to solve.

I would pour the remains directly in the garden.

Most plants like Epsom salts.

I would like to suggest somethings that has helped me more than Epsom salts.

Both are a cheap fix so if they don't help you are not out a lot of money.

Plus they are sold at your local grocery or that big box store that starts with a W.

Magnesium bath salts.  Get a spray bottle, mix 50/50 with water and spray your calves and feet.

Tonic water because it contains quinine.  I like the flavor and it is sparkling though it is easily mixed with fruit juice to add more flavor.

Taking magnesium and potassium might help also.

Use the diluted Epsom salt for annuals is generally beneficial as it adds two secondary macro nutrients if in balance with other nutrients. It is not recommended to give to perennials at this time of the year as they are already into senescence, preparing for winter dormancy. Plants mainly get sulfur from organic forms in soil so the availability will follow the curve of OM degradation and in late summer it is at the lowest point. Adding sulfate ions now will disrupt the natural process and cause the plants to start new growths that won't have time to harden off before winter.

Christopher Weeks wrote:First, is it bad for the septic? That's very much not my first place to put it, but winter is coming and we have pretty real winters here in northern MN.

I wonder if the salt concentration would be high enough that it could de-ice your walkways? Maybe at a part that is next to a magnesium-loving plant.

The frugalist in me says, "If your feet are clean to begin with, save the soak water for next time."

Magnesium bath salts.  Get a spray bottle, mix 50/50 with water and spray your calves and feet.  

My mother-in-law made a magnesium spray for us and it has been very helpful. My calves really appreciate it when they are sore.