Peonies: Getting Better Blooms, Avoiding Blackened Leaves & The Curious Dance of the Ants
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Question. I have two peony bushes that are thriving, but most of the buds stay small and don't mature into flowers. They get full sun from about 8 am until noon, filtered sun until mid afternoon, then full shade (from trees and a house.) They are mulched over winter with a natural cover of leaves and I usually spread partially rotted shredded leaves around the plants during summer. When I have to water them, it's with a sprinkler sitting 3 feet above the garden. I have not tested the soil pH. What might I be doing wrong?
----Frank in Concord Township, just west of Media, PA
Answer. Little bitty buds are common on young and recently re-planted peonies. If the problem persists after more than three years or so in the ground, the two best suspects are lack of sun and/or food. 'The book' says that your peonies are getting the bare minimum of sun, and maybe a little less than the minimum—but mine don't get much more than that (maybe even less), and they bloom just fine. 'Adding sun' is rarely a garden option, but if you can prune back some overhanging tree branches that are casting shade on the plants this winter, it could improve your odds of seeing big flowers in late Spring.
That leaves food; and the recommended timing for feeding peonies is downright weird. Most herbaceous perennials (plants that die back to the ground over winter and re-grow from their roots) should be fed in the Spring, soon after the new shoots emerge from the ground. But the experts say that with peonies, you should wait until the flower buds appear, later in the season. Then either surround the plants with a shovel or two full of finished compost (not the suspicious half-finished material you're using) or use an organic fertilizer that isn't high in nitrogen (the first of the three numbers on every packaged fertilizer's label).
Ah, but peonies also do a lot of underground growing at the end of the season to store energy for the winter, and many fanciers like to feed them then as well. Do this feeding before the leaves die back for the season—and remember; no chemicals! (Or even high-nitrogen natural fertilizers like horse or poultry manure.)
Stop covering the crowns with whole leaves in the winter; you're smothering the plants and potentially weakening them. And stop with the overhead watering as well—before disease problems come a calling. Water deeply—by allowing a hose to drip for an hour or so at the base of the plants—once a week when rain is scarce.
Question. Dear Mike: Every year after my peonies bloom, the leaves start to develop black patches, which is unsightly. Do they need to be fed, or are the plants diseased? Thanks,
---Susan in Boone, NC
Answer. The answer is almost certainly 'disease', Susan; a blight, to be specific. The cure for this common peony problem is good sanitation. Clean up everything around and under the plants—old leaves, mulch, whatever—as soon as you can in the Spring, and toss it all in the trash, not into a compost pile. Then mulch with an inch of fresh, finished compost—preferably 'hot compost' (meaning quickly or professionally made compost, not homeowner stuff that took a year or more to finish) for its additional disease-fighting properties. Apply this as soon as the newly-emerged plants are a few inches tall. Use no mulch other than compost, don't water from above, and you should be fine.
Question. Help, please! I planted a peony two years ago and got three flowers the first year. Last season it did very well, with at least three-dozen flower buds; but the buds were covered with ants. I've been told that the ants like the sticky sap or nectar in the buds, and if they don't come, the buds won't open. Is this true? Thank you,
---Mary Jane H.; no location
I want to try your boric acid ant control outside because there are ants crawling all over my peonies every Spring. (Why the heck are ants interested in peonies?) What is the best way to apply boric acid outside? Will it damage my plants in any way? Thanks,
---Conor in Wilmington, DE
Answer. Like forsythia and firethorn, peonies have specialized parts that pump out lots of extra sugar in the Spring. This sweet stuff attracts large numbers of ants, and has thus led to folk-stories claiming that the ants are necessary to get the flower buds to open. They are not; they're just there for the sugar.
Ah, but so is a type of wasp that looks like a winged carpenter ant. Commonly known as the 'Spring Tiphia', the highly beneficial females prey on the underground larval form of Japanese and other scarab beetles so effectively they can eliminate 80% of the grubs in your landscape—before they can become adult plant-eating beetles. And having sugar-producing plants in your landscape is the best way to attract these helpful creatures. (Rose growers—plant some peonies and forsythia and get even!)
Now for Conor's question. The low concentration of boric acid in ant traps is harmless to plants. But some folks fear that it could harm bees (or Spring tiphia wasps) attracted to the sugary bait. To avoid this, place outdoor boric acid baits in little jars with screwdriver holes punched into the lids. That way, only ants will be able to reach the bait, which will slowly kill the entire colony when it's taken back to their nest.