For my sins, I was listening to my local radio gardening phone-in on Sunday. A caller rang in and asked what to do about mildew on her Verbena bonariensis. Having listened to the phone-in on many occasions (and even having appeared on it. I don’t know how I keep my feet on the ground after the giddy heights of such fame) I had a pretty good idea what advice would be given. True to form, the guest expert suggested she spray them with a fungicide. I’ve lost count of the amount of times I’ve sworn at the radio during this particular programme and sadly Sunday was no exception.
The caller had explained her verbenas were in pots and as the guest rightly said, it was most likely underwatering that caused this type of mildew. And that’s where the sensible advice stopped, although he did allude to the fact the caller may not want to use a fungicide, which is a massive step forward for this show. The bottom line is, if you buy a perennial plant and leave it in a pot for more than about 6-8 weeks, you are making a rod for your own back, particularly if it’s summertime. Plants want to be in the ground. It’s unlikely you can meet the watering or nutrient needs of plants in pots long-term – you’ll either undo or overdo it. Hence the fact the verbenas in question were stressed out and riddled with powdery mildew.
But never mind verbenas in pots, Verbena bonariensis in the garden often has powdery mildew at the end of the year too. It’s spent the whole summer flowering itself silly, quite honestly, it’s knackered. If it’s growing happily somewhere, chances are it’s water-stressed because verbenas are only truly happy where they’re hard up for water. In some places the plants will die back to nothing, in some more sheltered locations they’ll stay evergreen and retain some of their basal leaves over winter. Either way, the powdery mildew will be gone come spring when the plant comes back into growth and the same is true of the plants in pots. All without the need for nasty fungicides (if you want to find out why using fungicides is bad for invertebrates, you might like to listen to my episode on Worms here).
So if, like Marjory in Cooden Beach (the names have been changed to protect the innocent), you have powdery mildew on your Verbena bonariensis, first ignore your radio. Second, get your verbena out of pots and into the ground. And third, spend the money you save on fungicide on more plants, because can you ever have enough plants?