How many tree nurtures can you do per day?

Whatever the true ceiling is, the free attempts run out long before it. Free nurtures refill at one per day at 4:00 AM and bank up to a maximum of three at once. Every attempt after those costs currency, given as both Vein Essences and Prismatic Energy Shards. For most players the daily cap matters less than how much Vein Essence they have.

The 25 figure is the most widely given ceiling, and it applies across all blooms rather than to each bloom. Moving to a different bloom does not get you more attempts. The 15 figure is usually described as the starting limit, with 25 as the maximum it can reach. The 10 figure is described both as the default cap and as the number of paid attempts allowed on top of the free ones.

Spending the attempts you have

Use your free nurtures before you spend anything. They generate prismatic energy and buff attempts at no cost, and once three are banked any further refill is lost.

The exception is the weekend. Vein Abundance surges run every Friday to Sunday and add a 50% bonus to the prismatic energy from nurturing, but only on three Nurture attempts per event. Keep at least three attempts, and the Vein Essence to pay for them, for that window. The Windborne Stamp Shop sells 10 Vein Essence a week, and unbought stock is lost when it resets, so that is the steadiest top-up.

Not settled: The game does not settle on a daily nurture limit. It appears as 10, as 15 rising to 25, and as a flat 25 shared across all blooms. It is also unclear whether these caps count only paid attempts or free and paid attempts together.