Bearded iris and peonies are longtime favorite perennials found in gardens and landscapes throughout Wisconsin. We look forward to annual displays of showy flowers in assorted colors. Occasionally these plants fail to bloom, requiring some investigating as to why.

Start by analyzing the growing site. Bearded iris and peonies both need full sun to flower, usually defined as a minimum of 6 hours of sunlight each day. Most full sun perennials will still grow foliage with less sun, but few if any flowers develop. Oftentimes site exposure may change as trees grow, so perhaps originally iris or peonies bloomed consistently in sun but then as shade increased, flower production declined. Solutions include either pruning trees, which may not be practical, or moving plants to a sunnier location.

Next, consider specific needs and culture of each species that may impact both flowering and overall growth. Bearded irises grow from thick rhizomes that should be at or just below the soil surface. Mulch, soil and debris accumulating may cause rhizomes to become too deep, which may reduce flowering. In addition, iris plants should be divided every 3 to 5 years, as overcrowded plants flower less.

July or August is a suitable time to divide and replant bearded iris. Replant rhizomes at or just below the soil surface in sunny locations with well-drained soil. When digging and dividing iris rhizomes, inspect them carefully for evidence of iris borer and bacterial soft rot, which often follows borers. Carefully cut away and discard infected rhizome tissue.

Blooming of peonies, like iris, is sensitive to planting depth. Peony buds, or eyes, should be about 1 to 2 inches below the soil surface. Planted too deep, peonies will still grow and have plenty of foliage, but few if any flowers. If overfertilized with nitrogen, peonies, like some other plants, can produce foliage at the expense of flowers. Also, keep in mind recently transplanted peonies may take a few seasons before blooming productively again.

Unlike iris, peonies do not require frequent dividing and can be left undisturbed for many years, developing into large clumps. As is the case with many perennials and ornamental grasses, large peony clumps can be divided as a means of propagating more plants. September is the best month for dividing and replanting peonies.

Both peonies and iris benefit from deadheading spent flowers after blooming to prevent spending energy on fruit production. After bloom it is important to allow foliage to remain, so plants can produce energy for future growth and development. When fall arrives, however, it is beneficial to remove peony foliage to reduce potential disease development.