Cherish a Late Bloomer!

By Hubert Ling

While having your shrub bloom in June is generally not considered very late, you might think a swamp azalea should bloom in mid-April or at least in May. But no, swamp azalea fully leafs out first, and in its own good time graces our yards with sweet smelling, honeysuckle-like blossoms in June and even in July.

Our native swamp azalea is widespread in the Eastern US from Maine to Florida and west to Texas. In NJ, it has been reported from all 21 counties.

Swamp or sticky azalea, Rhododendron viscosum, has been a garden favorite in England and America since 1680. The modest 1.6 inch white to light pink flowers form respectable, showy clusters, but the spicy, sweet, strongest fragrance sets this gem apart from all its more exuberantly colored scarlet or hot pink competitors. Several somewhat more showy cultivars of swamp azalea are also available. These include ‘Delaware Blue’, ‘Lemon Drop’, ‘Lollipop’, ‘Millennium’, ‘Parade’, ‘Pink Mist’, ‘Pink Rocket’, ‘Pink and Sweet’, and ‘Viscosum’. I did mention it has been in cultivation for over 300 years. Swamp azalea is also good for cut-flowers.

Rhodo is Greek for rose and dendron means tree. Viscosum means sticky and refers to the sticky product of glandular hairs present on the outside of the trumpet shaped flowers. Despite being named a tree, swamp azalea is just a moderate sized shrub generally only 4-6 feet tall and has a similar spread. It is a slow growing plant which thrives in rich, damp, acidic soil. The plant is sometimes found in semi-shady areas with moderate water.

Swamp azalea will tolerate sand, clay, and temporary standing water, but it will not survive being constantly flooded. It will also not survive in full sun under dry conditions, and is not found in basic, limestone regions. It is generally listed as an obligate wetlands or facultative wetlands plant.

Swamp azalea is resistant to rabbits, but deer will gradually chew it down to a short stub. In addition, don’t plant it near a walnut or butternut tree since it is sensitive to the toxic juglones which these trees release underground. Azaleas, including swamp azalea, are susceptible to several insect and disease agents, however a healthy plant growing under its preferred conditions is generally resistant to serious damage. The plants have little to no resistance to salt spray or saline soil.

Propagation is by root cuttings, layering, and seed. Root semi-woody cuttings in late summer and air layer in fall. Seeds can be germinated in a peat moss-sand mixture that is never allowed to dry out or remain waterlogged. Germination should take place in ten days; they do not need pretreatment. Also, be careful to not allow the seedlings to dry out. If the plant is in an ideal location, it will also spread very slowly by suckering. The website, backyardgardener. com, is chock full of all sorts of gardening information on this azalea and much more.

Swamp azalea attracts hummingbirds, long-tongued bees, and butterflies, and in the fall the leaves turn a colorful mixture of orange, purple, red, and yellow.

Members of the genus Rhododendron, such as swamp azalea, contain the potent compound andromedotoxin (grayanotoxin). This toxin is present in all parts of the plant and may even show up in the honey (known as mad honey). However, since only long-tongued bees can sip nectar from swamp azaleas, which have very long corolla tubes, humans should be safe eating honey in areas where swamp azaleas abound. Honey poisonings, however, have occurred involving rhododendrons or mountain laurels that have much shorter corolla tubes, and care should be taken to prevent pet, livestock, and young children from ingesting any part of any Rhododendron

Think of swamp azalea if you have a protected, moist, semi-shaded spot in your yard. It grows well with partridge berry, Jack-in-the-pulpit, blue lobelia, Solomon’s seal, royal fern, cinnamon fern, Pinxter azalea, wild leeks, and sweet pepperbush. It will do well in an acidic, humus-rich soil at about pH 5. It has rather shallow roots so give it a layer of leaf mulch to keep it moist but aerated.

Editor’s Note: Hubert Ling is Horticultural Co-Chair of the Native Plant Society of New Jersey. He can be reached at milhubling@ verizon.net.

The Pennsylvania Horticultural Society has selected six new plants as part of its Gold Medal Plant Program for 2023. All six plants are native perennials, shrubs and trees. Gold Medal Plants are selected for ornamental attributes; they can be found in local garden centers; are relatively easy to cultivate; and support a host of ecological functions.

Spigelia marilandica has tubular red flowers with yellow tips at the end of spring into the early summer. It can be grown in full sun, but also thrives in full shade. It attracts the Ruby-throat Hummingbird to the garden. This clumpforming perennial will expand over time. Once established, it can also spread by seeding around in the garden. Reaching two feet tall at maturity, it is also fits nicely into a relatively small garden.

Vernonia lettermannii

‘Iron Butterfly’ is a new selection of the native ironweeds. This relative of the asters is covered with vivid purple flowers in later summer to early fall. It is a great late season pollinator plant. Reaching about 18 inches tall, this clumping perennial can be grown as a single specimen, but looks great when planted in masses where it combines