Ask Burton: This week, we’re looking at a favorite container plant for the season – how to keep rosemary looking its best. Q: I plant cone-sheared rosemary in my front patio pots each year, for something taller and pretty during the winter. Last year, my rosemary got great big dead patches in it without much warning – whole sections of it died. What happened, and how do I make it not happen this year?

A: Rosemary is a great plant for this time of year – it’s evergreen, aromatic, and taller specimens bring much-needed height to winter color pots. It’s not hard to grow rosemary, but there are a few things you’ll need to do to keep it in the best shape.
• Sunshine – Rosemary plants appreciate good sunlight, and won’t thrive well if they’re far up under a patio cover. Half a day or more sunshine will make them happy.
• Don’t over water – Rosemary like to be a bit on the dry side, all the time. Plants which are watered too much will wither and fail, or grow sluggishly at best. Make sure your pots have good drainage holes, and that the holes are draining well and are not blocked.
• Keep the top of the plant dry, too – It’s almost never a problem in hot weather, but rosemary is prone to powdery mildew in cool, moist conditions. Don’t spray the top of the plant when watering (water the soil, not the plant). Cone-sheared rosemary is especially dense, and gets poorer airflow through the plant as a consequence, making mildew more common. Apply a fungicide early if you start to see white bits of powdery mildew. Powdery mildew is what likely caused your dead patches last year.