The old man collected the ash and sprinkled it over the cherry tree.

- Ash as a Fertilizer:
Ash is commonly used as a natural fertilizer due to its nutrient content. When plants burn, they release essential nutrients into the ash. These nutrients, such as potassium, phosphorus, and calcium, can benefit the growth and development of other plants. By sprinkling ash over the cherry tree, the old man is providing it with these essential nutrients.

- Potassium Content:
Potassium is a vital nutrient for plants as it promotes overall growth, improves root development, and enhances resistance to diseases and pests. Sprinkling ash, which contains potassium, helps the cherry tree receive a sufficient supply of this nutrient, thus improving its health and productivity.

- Phosphorus Content:
Phosphorus is another essential nutrient for plants, especially during their flowering and fruiting stages. It aids in the development of strong roots, promotes flower and fruit formation, and enhances overall plant vigor. The ash collected by the old man may contain phosphorus, which can benefit the cherry tree by supporting its reproductive processes.

- Calcium Content:
Calcium plays a crucial role in maintaining the structure and strength of plant cell walls. It also helps in the transport of other nutrients within the plant. By sprinkling ash over the cherry tree, the old man is potentially enriching the soil with calcium, which can contribute to the tree's overall health and resilience.

- Other Benefits:
In addition to its nutrient content, ash can also have other positive effects on plants. For example, it can help to raise the pH level of acidic soils, making them more suitable for plant growth. Ash can also act as a natural pesticide, deterring certain pests and protecting plants from their damage.

In summary, the old man collected ash and sprinkled it over the cherry tree to provide essential nutrients such as potassium, phosphorus, and calcium. This practice can improve the tree's growth, fruit production, and overall health. Additionally, ash can have other benefits like raising soil pH and acting as a natural pesticide.