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Wilting Peonie and Iris Blooms

Posted: Wed May 27, 2015 4:52 pm
by Lisa
Our peonies and iris were blooming beautifully until dark woody mulch, obtained from a nursery, was lightly applied. Within several days the unopened blooms turned brown and began wilting. The hollihocks, which had not yet bloomed, turned yellow near the ground. Clearly these plants were in severe distress. The mulch provider had no other complaints. The mulch was removed last evening and today the plants are perkier. Is this a pH issue? If so, how can the damage be minimized? Shenandoah Valley, Virginia

Re: Wilting Peonie and Iris Blooms

Posted: Fri May 29, 2015 5:01 pm
by lorijones
Peonies and iris should not be mulched over their crowns and rhizomes. Peonies are prone to crown rot and mulch should be kept away from the stems to avoid excess moisture buildup in the soil. Iris rhizomes are modified stems and should not be completely covered with soil or mulch.

That being said, it is possible that the mulch may have either been too "hot" or perhaps "sour". Did it have a strong smell? It is unlikely that the mulch could have created a pH problem. pH changes occur slowly over time - not as quickly as your plants declined.
Problems can arise when mulch is stored in large piles that aren't properly turned and aerated. The centers of these large piles can get hot and the lack of oxygen can cause toxic gasses to build up. These gasses are released when the mulch is spread and cause the damage you noticed on your plants. This is more common with hardwood mulches. The best way around this is to let the mulch air out before you spread it on the garden. This will allow the toxic gasses to dissipate. Damaged foliage can be trimmed off and the plants should recover.