Last month’s article “It’s Raining, It’s Pouring, My Garden is Growing” discussed the how and why to build a rain garden. In this month’s article I will share some of my favourite plants that are well suited to rain gardens. These plants can handle both having their feet wet on occasion, sometimes for days on end, yet can also tolerate long periods of dry soil.
The following plants are listed in alphabetical order by scientific name. Plants with hyperlink are ones that have a complete description on the Plant of the Month pages of this website.
The Sunny (to partly sunny) Rain Garden
Swamp Milkweed (Asclepias incarnata) – 3′ to 4’ tall, a monarch host plant and an excellent nectar source for butterflies and even hummingbirds. The juice of this wetland milkweed is less milky than that of other species. It tends to bloom twice in a growing season when in gardens. Rare occasional white specimens are found in the wild and these have led to cultivars such as “Ice Ballet.”
Marsh Marigold (Caltha palustris) – up to 18″ tall, this is one of the first wetland flowers to bloom in spring. Seeds should be sown as soon as they’re ripe and cannot dry out before sowing. Seedlings do not flower until the third year following germination. Plants also reproduce easily by division in early spring as the plants are emerging.
Boneset (Eupatorium perfoliatum) 3′ to 4′ tall, has very distinct, bold leaves with a crinkly texture and the pure white flowers bloom for a long time. Nectar or and pollen of the flowers attracts many kinds of insects and it is a host plant for several moth species. Seeds need light to germinate in the fall, and sow thickly as germination rates are typically low. Stratification for at least 30 days will increase germination percentages. Seeds will last up to 3 three years if stored in the fridge. Boneset can also be propagated by root division in the fall just as they go dormant, or in early spring just as the first shoots appear
Joe-Pye Weed (Eutrochium maculatum) 5′ to 7′ tall, the flowers have a light vanilla fragrance that becomes more intense when crushed. An important food source for butterflies, bumblebees, green metallic sweat bees, and skippers, it is also the host plant for several moth species, including the Ruby Tiger Moth.
Bottle Gentian (Gentiana andrewsii) 1′ tall, it is especially valuable to bumble bees, just about the only insect with enough strength to force its way into the closed flower. Plant tends to lean at maturity, so plant among sturdier plants for support. If left undisturbed, plants in optimum growing conditions will naturalize over time into large clumps.
Water Avens (Geum rivale) 1’ to 2’ tall, the intricate, droopy flowers of Water Avens will add a touch of elegance to your garden and are best enjoyed up close. They provide a long bloom time and turn into ornamental, fluffy seed heads. Water Avens maintains a clumping form and looks its best when planted en masse. The fragrant flowers were once used to flavour ales, and the roots can be boiled to make a chocolate-like drink.
Spotted Jewelweed (Impatiens capensis) AKA “touch me not”, this plant will get up to 5’ or more in height and will eagerly self-seed and quickly cover moist areas with beauty and wildlife value. Hummingbirds and butterflies seek nectar, and several native bees (listed by the Xerces society as of special value to bumblebees) collect pollen (it is listed by the Xerces Society as of special value to bumblebees). The juice from Jewelweed stems contains a compound called lawsone, which has shown to have antihistamine and anti-inflammatory properties. It is said to relieve itching from Poison Ivy, mosquito bites, and Stinging Nettle and has also been used to treat athlete’s foot.
Blue Flag Iris (Iris versicolor) At 2’ to 3’ tall, this is a personal favourite of mine. Seeds require at least 4 months of cold, moist stratification to germinate and will take 2 years till they produce flowers. To propagate vegetatively, the roots can be divided in early summer.
Cardinal Flower (Lobelia cardinalis) 3′ to 4’ tall, this is a hummingbird magnet in the garden. Although relatively short lived (usually 2-3 years) it can carry on in your garden by dividing it or moving it every year or two. This plant is at its finest when growing with minimal competition in forested wetlands. Note that commercial garden centers often sell cultivars of this plant, that may or may not be as valuable to wildlife as the true species.
Blue lobelia (Lobelia siphilitica) 2’ to 4’ tall, the nectar attracts butterflies and native bees and occasionally hummingbirds. Pinch back the plants to make them bushier. Blue Lobelia will produce offsets around the base that will generate their own roots. These can be removed with a sharp knife in the spring or fall, being careful to retain their roots, and transplanted. These small offsets are delicate, so care should be taken not to bury them under thick mulch.
Monkey Flower (Mimulus ringens) 1’ to 3’ tall, adds a wonderful, refined look to wet sites and will spread slowly by rhizomes to take on a bushy look once mature. Its snapdragon-like flowers have a long bloom time, which is great for bees and gardeners alike. The dried seed heads provide great textural interest over the winter months.
Golden Grounsel (Packera aurea) 1′ to 2’ tall, it puts on a luminous and long-lasting display of golden- yellow flowers in the springtime. It is a robust, bold- textured groundcover that will spread by both rhizomes and seeds.
New England Aster (Symphyotrichum novae-angliae) 3′ to 5′, this is a host plant for Checkerspot and Crescent butterflies and others, and for several moth species. New England Aster has a tendency to become root-bound and will benefit from dividing the plant every 3 to 4 years. Pinching back the stems a few times before mid-July will help to make the plant bushier and eliminate the need for staking.
Blue Vervain (Verbena hastata) up to 5′ tall, it puts on a majestic display of candelabra-shaped flower clusters in mid-summer, filling the garden with accents of violet-blue. It maintains a clumping habit and makes a great structural plant. The rigid stems and seed heads stand tall through the winter to provide excellent seasonal interest.
Buttonbush (Cephalanthus occidentalis) 5’ to 10’ tall, this shrub produces a unique white round flower head that is highly attractive to bees and butterflies. It can be pruned back in the spring if necessary. The shrub requires full sun but may tolerate some shade. Otherwise, buttonbush is extremely resilient in all types of temperatures and conditions. It is important to note that the leaves of this plant are toxic to humans.
Meadowsweet (Spiraea alba) 3′ to 6’ tall, larval host for Spring Azure butterflies. Blooming for 1 to months, the pollen and nectar attract a wide range of bees, bumblebees, moths and other pollinators. It takes well to pruning after flowers have finished blooming. It does spread by rhizomes and may work better in a larger rain garden.
The Shady Rain Garden
Yellow Lady’s Slipper (Cypripedium parviflorum) 1’ to 2’ tall, propagating these showy yellow orchids from seed is complex. The seeds are extremely small and contain no endosperm (the energy reserves in most other seeds) and cannot survive without a symbiont soil fungus to absorb nutrients for it. Most commercially grown Lady’s Slippers are germinated in the lab in a special medium, or by tissue culture, can take a year or more to germinate, and up to a decade or more before they flower. This is why lady’s slipper orchids are so expensive. If someone is selling you a Cypripedium orchid at a bargain price, chances are it was wild harvested. In the garden, plants that have grown very large (with at least 30 shoots) should be divided to keep the plant healthy.
Virginia Waterleaf (Hydrophyllum virginianum) 1’ to 2’ tall, is a reliable ground cover that puts on a verdant display of leaves early in the spring. Delicate -looking flower clusters rise above the leaves in late spring to dot the landscape with pastel purple hues.
Wood Lily (Lilium philadelphicum) 2’ to 3’ (occasionally up to 4’) tall, the stunning flowers add fiery red/orange accents to the summer garden, while its whorled leaves add an interesting texture. It has a very elegant look overall and maintains a clumping habit. Pair it with plants of similar height as it does not like competition. It’s slow to establish but well worth the wait.
Cardinal Flower (Lobelia cardinalis) – see above
Royal Fern (Osmunda spectabilis formerly O. regalis) 3’ to 6′, it is one of the largest ferns in non-tropical North America. Fronds typically turn yellow to brown in autumn. Spores are located in brown, tassel-like, fertile clusters at the tips of the fronds, thus giving rise to the additional common name of flowering fern for this plant.
Golden groundsel (Packera aurea) – see above
Marsh Fern (Thelypteris palustris) 1’ to 2’ tall, this fern spreads to form a lush green ground cover in moist soil. Although it does well in sunnier rain gardens, it also thrives in moderately dense shade in my gardens. The Marsh Fern often forms dense colonies of leaves, it provides good cover for the smaller kinds of wildlife.
Witch-hazel (Hamamelis virginiana) 8′ to 20′ tall, it prefers moist, acidic, organically rich soils and will tolerate heavy clay soils. One of the last shrubs to flower. the stem-hugging clusters of fragrant bright yellow flowers, each with four crinkly, ribbon-shaped petals, appear along the branches from October to December.
Northern spicebush (Lindera benzoin) 4’ to 15′, this fragrant (spicy) host plant for the Spicebush Swallowtail butterfly produces beautiful, tiny yellow flowers in the spring and makes a great alternative to the non-native Forsythia. Shrubs are either male or female, and if you’re lucky enough to get a female, you are apt to get bright red, spicy smelling fruit in late summer. In the fall, the leaves are brilliant yellow.