The apple compost, "apple soil," is now complete.

At Hoshino Onsen Tonbo no Yu, we hold an "Apple Bath" event every autumn. We collect the apples that float in the bath and make apple compost called "apple soil." This year, we will once again distribute the fluffy apple soil, which has been completed after surviving the harsh winter in Karuizawa, to those who use Tonbo no Yu.

How apple soil is made

The apple soil was carefully cultivated by the staff of Tonbo-no-Yu in a corner of the forest in the Hoshino area. This process took approximately five months. Dried and finely chopped apples were mixed with potting soil, and the soil was turned twice a month to deliver oxygen deep into the soil. Through slow aerobic fermentation by aerobic microorganisms, the sugars and fibers of the apples were broken down. This removed the causes of damage to plant roots, resulting in nutrient-rich, clean, and fully matured soil.

The effects of apple soil

The sugars, acids, and minerals in apples promote the diversity of microorganisms in the soil, help to create granular soil structures, and make it "delicious soil" for plants. The organic acids in apples, such as malic acid and citric acid, dissolve minerals that have hardened in the soil, making them easier for plants to absorb. The polyphenols in the peel activate some beneficial microorganisms during the decomposition process, which is expected to help promote healthy plant growth.

As a sustainable initiative

In organizing the apple bath event, we are working with local farmers with sustainability in mind. One example of this is using apples of various sizes that don't meet standard specifications. Furthermore, we believe that transforming the apples after use into something that can be used for home gardening is one form of sustainable consumption and production in the region. Hoping that this will be an opportunity for people to think about the environment and take action, we will begin distributing the apples on Earth Day (April 22, 2026).