How to Use the Bonsai Watering & Fertilizer Calculator
Because bonsai pots hold so little soil, moisture and nutrients get used up much faster than in a regular potted plant, which means the care schedule needs closer attention. This calculator takes your species type (conifer, broadleaf, or succulent-type), pot diameter, and season, then recommends a watering interval and a fertilizer concentration and schedule.
Conifers tend to dry out more slowly, so they can go longer between waterings, while broadleaf trees transpire more through their leaves and need water more often. Smaller pots hold less soil and dry out faster, so they need shorter intervals, while larger pots can go longer. Summer heat speeds up evaporation, so intervals shrink, while winter dormancy calls for much longer gaps to avoid root rot.
As a general rule, feed diluted liquid fertilizer regularly during the active growing months from spring through fall, then stop entirely during winter dormancy. It's also worth pausing fertilizer right after repotting or whenever the tree is stressed by pests, since feeding weak roots can make the damage worse.
Frequently Asked Questions
During dormancy, growth nearly stops and water use drops sharply. Wait a few extra days after the soil surface dries before watering again to help prevent root rot.
Skip fertilizer during winter dormancy and for 2-3 weeks after repotting. Feeding a tree with stressed or freshly cut roots can worsen root damage.