Epsom Salt also known as Magnesium Sulphate. Will rectify magnesium deficiency of which will give the same appearance as Iron in that it will green-up yellowing leaves.

Here the "jury" is still out. Only if you have a magnesium deficiency it will provide a temporary fix. It is a super abundant mineral in the Earth's crust and rarely is there ever a deficiency. Some people swear by it though. It's PH neutral so it won't hurt anything. I know it's good for bee stings & sore muscles.

I had lots of old gardening books which recommended Epsom Salts especially in regard to tomato and rose growing.

Thank you all for your replies. Waste not want not. Instead of pouring my epson salt footbath down the drain I will sprinkle it around my garden.

it certainly does help replace magnesium and is a recommended treatment to correct mild chlorosis in plants. though lack of magnesium isn't the only cause of chlorosis.

I've heard of people using it to restore the blue of hydrangeas that are tending to pink. Depends on your soil pH if that would be useful to you.