Healthy plants produce lush foliage and undamaged leaves. Yellow mottling or spots on leaves usually indicates a disease or insect problem, but yellowed leaf tips require careful attention to the climate and culture of the plant to diagnose properly. Yellow leaf tips and margins generally have an environmental cause that is quickly remedied once found.
Excessive heat, dry air and bright sunlight results in leaf scorching. Scorched leaves develop dry yellow or brown tips and margins. Foliage shaded on the interior of the plant rarely experiences yellow tips and still appears healthy since these leaves aren't exposed to the light. Scorching typically occurs during hot, dry weather. Moving potted plants to an area where they receive afternoon shade helps prevent scorching. Bedding plants may benefit from an extra watering each week until the hot, dry weather passes.
Irrigation concerns cause leaf yellowing. Overly wet soils result in leaves turning uniformly yellow or dropping off without a color change. Underwatered plants develop brittle yellow or brown leaf tips. Eventually the entire leaf wilts and drops off the plant. Most plants require watering when the top inch of soil begins to dry and before yellowing or wilting occurs. Mulches help prevent soil drying so the soil around the roots retains the proper amount of moisture for healthy plant growth.
Fertilizers contain salts. In garden beds, the salts leech out and become diluted in the soil. The fertilizer salts have nowhere to go in potted plants so they build up in the soil. Yellowing leaf tips and a white chalky buildup on the soil and interior of the pot rim indicate salt issues. Water potted plants until the excess moisture drains freely from the bottom of the pot, flushing out the salts, once weekly. Soil severely affected by salt buildup may necessitate repotting the plant in fresh soil.
Burning occurs when fertilizer comes in direct contact with foliage. Fertilizers require dilution, which normally occurs within the soil. When fertilizer dust or liquids splash onto the foliage, the undiluted chemicals cause yellowing tips or blotches on the affected leaves. Too much fertilizer in the soil also results in all-over leaf tip yellowing. Apply fertilizers only at the package recommended rate and rinse the foliage with clear water after application to prevent fertilizer burns.