Companion Plants for an Oklahoma Garden
Leonard O. Miller, D.D.S.
Rhododendrons are the featured plants at LenDonwood Garden in Grove, Oklahoma. However, without other supportive plants we would have a very seasonal garden. These plants are often trees and ground covers that combine with rhododendrons to give us a pleasing balance of structure and color to the landscape. We have a few shrubs that need the same exposure as rhododendrons, but that limits the space for our favorite plant, the King of Shrubs.
The dogwood ( Cornus ) grows naturally in our area making this tree easy to grow. There are twenty varieties of them in the Oriental Garden where they add spring and fall color. About 200 of the 400 rhododendrons are found in the Oriental Garden. If you have mature, taller trees in your garden, you could produce dense shade that will prevent rhododendrons from blooming. Rhododendrons seem to bloom better with some morning direct sunlight.
The ground cover that we selected to grow under these two tiers of trees is Hosta . Hostas are the most popular shade plant because of the leaf textures and color they bring to this heavy shade. If you are a plant collector, you have no problem getting varieties that suit your taste. My favorites are 'Shade Fanfare', 'So Sweet', 'Brim Cup', 'Gold Standard' and 'Sun Power'. The hosta that attracts the most attention, however, is 'Sum and Substance' with its huge gold-green leaves. We have seventy-five varieties and our most interesting collection is of the dwarf types found in the English Terrace Garden.
Photo by Leonard O. Miller
An evergreen plant that is used as an edger along the paths of the Oriental Garden is Liriope . This plant is tough and comes in dark green types, such as 'Big Blue' or the variegated forms with yellow and green stripes. They tolerate shade and work well with rhododendrons.
Lamium is a ground cover that is gaining popularity and is replacing ivy as a shade ground cover. My favorite is 'White Nancy' for its white flowers and good white and green foliage. Lamium likes cool weather and at LenDonwood it looks a little rough in the hot summer. It is great in the spring and fall, however, spreading slowly among the shrubs. Stay away from the rampant lamiums because they will climb and grow too fast, invading other plants. The closely related Lamiastrum 'Herman's Pride' is seemlier with silver and green leaves that is not invasive.
Photo by Leonard O. Miller
Brunnera macrophylla is one of my favorite spring flowering perennials with its tiny baby-blue flowers that grow in clusters. With some summer irrigation it survives in our hot summers. It will reseed readily and you will have dozens next year. I grew my first plants from seed. Only three plants came from that first germination, but now I have hundreds. Brunnera macrophylla 'Varigata' is a horse of another color. The variegation comes from the stem and not the roots. If the stem freezes the plant will lose its variegation. I mulched it heavily the first year and it pulled through the winter. The next year it lost its variegation and died. I wouldn't recommend this plant if you have hard winters. ( Brunnera macrophylla is hardy to Zone 3.) Hostas can give you that same look.
Digitalis (foxglove) comes on after the rhododendrons finish blooming and there isn't one I don't like (double negative equal a positive!). Digitalis 'Mertonensis' has the best foliage. If you want a lot of foxgloves let the flowering spikes go to seed. You can take the seed pods to a new area and sprinkle the seed over a prepared seed bed to germinate in the fall. These will then bloom in the spring. Avoid hoeing seedlings but pull weeds by hand and save the seedlings, leaving 1 foot between plants. Watch for the seedlings around the old plants and you can transplant extra plants around October 1st.
An unusual woodland plant that is prospering here at LenDonwood is the hardy cyclamen. After visiting the Smith Garden in Sherwood, Oregon, I thought I would try them in Oklahoma. Cyclamen is a winter plant and goes dormant in the summer. The tiny bulb-like plant grows from a corm and has interesting variegated leaves. They can bloom with small pink flowers in the fall or the spring and make a great plant to place around and below rhododendrons.
One of the rare perennials that we grow is Corydalis 'Ophiocarpa'. This has blue ferny or lacy foliage with small yellow flowers. One volunteer pulled up all our plants thinking they were weeds. I thought this plant would be lost, but seedlings came up that fall and we still are enjoying this interesting plant.
Here in Oklahoma, the botanical gardens recommend exceptional plants for their plant evaluation program, called Oklahoma Proven. My submission was an Ajuga - A. 'Catlin's Giant'. This is a fast growing, purple-leaf ground cover. It has blue spiked flowers, but its best asset is the rosette foliage which is one third bigger than the common ajuga. It is hardy to Zone 3, but I have seen winter damage here in Zone 6, so leave some loose oak leaves over the plants.
A discussion of companion plants would not be complete without including ferns. We have several favorites, such as Athyrium niponicum 'Pictum', called the Japanese painted fern, which has purple, gray and green variegated foliage that grows 2 feet (0.5 m) high. Another fern which I like is Felix-femina , the lady fern, which has 30-inch (75 cm) lacy, lance-shaped fronds. If the soil is moist you will be pleased with this showy fern. Most ferns will enjoy the same exposure as rhododendrons but, remember, if you let them dry out they will go dormant or die.
My last companion plant is the Pulmonaria or lungwort. These foliage plants have silver to white spots on the leaves. Since I like variegated plants, the more white or silver the better. Those that fit the bill are 'Margery Fisk', 'Bertram Anderson', 'Roy Davidson' and 'Excalibur'. Another with great spring flowers is 'Little Star'.
Many plants enjoy the same acid, moist and high humus soils as the rhododendron. Actually the list is endless and you may enjoy others that are complimentary to our favorite plant. Annuals are helpful to provide color once the rhododendrons quit blooming. That is what is great about gardening, no two gardens are the same and there are endless possibilities. Come and see us at LenDonwood, where the King of Shrubs is in its finest cloth.
Len Miller wrote about LenDonwood in the Winter 1997 issue in his article "LenDonwood Garden: Building a Public Garden in Oklahoma."