A melastome that's watered correctly and getting good light can still struggle for a reason that's easy to overlook entirely: soil pH. Most species in this family prefer slightly acidic conditions, and planting in neutral or alkaline soil — common in many municipal water supplies and standard potting mixes — can quietly limit nutrient uptake even when every other care step is right.
What "acid-loving" actually means in practice
Most melastomes do best in a soil pH somewhere around 5.5 to 6.5. Outside that range, particularly on the alkaline side, certain nutrients — iron in particular — become chemically less available to the plant even if they're technically present in the soil, leading to yellowing new growth that looks a lot like a nutrient deficiency because, functionally, it is one.
Building the right mix
An azalea, camellia, or general acid-loving-plant potting mix is a reasonable off-the-shelf starting point. Building your own is straightforward too: a base of quality potting soil amended with peat moss or pine bark fines will nudge pH into the right range while also improving drainage — a combination that suits most of the genera covered on this site, from Tibouchina to epiphytic types like Medinilla.
Fertilizing appropriately
A fertilizer formulated for acid-loving plants helps maintain the right conditions over time, rather than gradually pushing soil pH upward the way some standard all-purpose fertilizers can. Apply at half strength during active growth, and hold off entirely during winter dormancy — see our winter care guide for the full seasonal adjustment.
If a melastome's leaves are yellowing despite consistent watering and good light, checking soil pH before assuming a watering problem often finds the real answer faster.