If you’ve been growing or starting your own pansy seedlings, you may have noticed a yellowing of the tips and edges of the new growth. This generally happens because the new growing plant is in a too-alkaline soil and the plant and is starved for iron.
The solution to this is to acidify the soil so the pH is 5.4–5.8.
You can do this carefully by adding vinegar to your irrigation water – a teaspoon a litre to start (approx 2 tablespoon per gallon)
Stop adding vinegar as soon as the yellowing stops.
It is also possible to add chelated iron to water and spraying it on the leaves as a foliar spray. Follow directions on the iron product for proper measuring ratios.