The best way is to reuse the soil after you have cut off the shoots. Make compost using the leftover wheatgrass, add some garden soil.

And then use new compost for growing wheatgrass. Then repeat it again and again.

Planting tray with wheatgrass after cut off blades, flipped over that roots on the top.
Make compost after cutting off wheatgrass.

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I cannot recommend any specific composter. Because I live in an apartment, and I don't have any backyard. I have nowhere to put my composter, if only near my bed. )) So, unfortunately, I throw away the used soil due to the impossibility of recycling. But I know a lot of people who have a backyard with a composter. They are happy that they always have excellent quality soil/compost for growing wheatgrass at home.

Black tumbling composter on the white background.
Just an example of a simple tumbling composter.

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By the way, about homemade compost. Using this can seriously save your money, instead of buying a big bag of garden soil each month. You can also compare all these costs:

  1. the cost of a daily shot of fresh wheatgrass bought at a sport/juicy bar;
  2. the cost of one dose using dry wheatgrass powder unknown quality purchased from Amazon;
  3. and the cost of the shot of homemade wheatgrass highly quality;

Then, the enthusiasm to spend some personal time growing wheatgrass at home will increase significantly.

Good luck!