For myriad problem spots in yard and garden, phlox has got you covered.
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Although I fear taking exception to my revered Sackville-West, I find myself disagreeing on another point. My best phlox bloom comes in full sun, not light shade. Your choice, but either way, the single most important planting tip I can give you about phlox is not to crowd them. Plant them a good 2 feet apart to improve both their looks and health. They’re far less likely to get mildew if there’s good air circulation around them, although a prolonged spell of damp, warm weather is bound to cause cold to coat the leaves a thick, sick gray. No permanent damage—it just looks awful.
I’ve always dusted with sulfur or sprayed with Benomyl to counteract mildew, but I’ve just learned that the fungicide, Funginex, is supposed to be a sure cure. It’s been around for several years, long enough for that great gardener, Glenn Waruch at Claire’s Garden Center in Patterson, N.Y., to recommend it. I’ve used it for other things—spraying dogwoods, for example—but never as a cure for mildew on phlox. I’ll try it on lilac, too.
Other care and feeding tips? Phlox want lots of water but never from overhead. Wetting the leaves can cause mildew. Give the earth below a good soaking instead. They also want a rich soil and fertilizer in early spring. I prefer bone meal or an organic plant food. Although it seems paradoxical, you’ll get thicker growth by heavily thinning old plants—pinching out even half the new shoots will not be too drastic. Last summer I hadn’t the heart to thin Blue Lagoon, a pastel lavender-blue, as I knew I should. It was a knockout, big and fat, until it fell over flat on its lovely heads. The roots simply couldn’t support such a heavy load.
So even if you’re buying new plants from the nursery to set out this month, don’t be afraid to cut out some shoots. Three or four stalks are plenty to grow into a great bushy plant that will stay upright as it should. If you snip dead flower heads, you’ll
get repeat bloom from side shoots, though not quite so tall as the first. Also, you will keep the plant strong by preventing the formation of seeds, and the small forest of ugly magenta volunteer seedlings that sprout from them and ultimately crowd out the mother plant.