A COLORFUL BLUE FLOWERING GROUND COVER
Bright blue flowers, dark green foliage and its low-growing habit combine to make the Lithodora a colorful plant to use in the sunny landscape. Along with Ceanothus. Ajuga, and Gentians this plant is one of the best blue flowering ground covers.
There are few flowering plants that have such a contrast of bright blue flowers and deep green foliage, as does the Lithodora. In earlier time this plant was known as Lithospermum diffusum, but today is referred to as Lithodora diffusa.
My first experience with this plant dates back about 35 years ago. At that time I planted it as a ground cover at the base of a bed of roses. The late May early June flowers were very attractive, coming into bloom just as the roses burst into their first seasonal bloom. Then as the season progressed the plants produced a few additional flowers from time to time, and the dark green foliage did a nice job of covering the soil. The cover provided by the Lithodora cut back a bit on the need to water, saving time and money. But the bonus was, the plant went to seed the following year, and dozens of plants covered the entire rose bed, providing an outstanding color combination. That one experience sold-me on the value of this plant in the garden. Since, I have used it in rockeries, as a ground cover or simply as a low growing plant at the edge of flower and shrub beds.
Lithodora is also a nice evergreen ground cover to use in containers, window boxes or even seasonal hanging baskets. Recently I saw it used very effectively at the base of a rockery, between the rocks and sidewalk, providing an attractive low-maintenance ground cover. In such a spot, the dense foliage seemed to do a nice job of crowding out the growth of nuisance weeds and grasses.
The flowers are quite small, approximately half an inch across. They cover the plant in May and June with additional flowers sprinkled throughout the rest of the summer. The attractive dark green leaves make a very attractive background for the showy flowers. The leaves are up to about an inch long, narrow in width, and quite dense.
In my garden, the plant seldom reaches a height of more then 3 or 4 inches, but if it is crowded, it will attain a height of 6 to 12 inches. It is not unusual for a single plant to spread 2 to 3 feet in width. When given average conditions the plant is very bushy. It is low and clings to the ground, and will follow the contour of rocks and hang nicely from retaining walls without any kind of support.
If Lithodora has one drawback, it is that it can be susceptible to freeze burn if weather conditions are a bit extreme. This burn shows up in a blackening of the leaves and may even freeze the stems. When, or if this condition occurs, the plant will need to be sheared back, in order to keep it looking nice. I have lost a couple of plants over-the-years, simply because I had to prune them too severely. However, they seem to be quite dependable up to 1,000 feet elevation. In my garden, where the temperatures have dipped as low as 3 degrees above zero, the plant has done quite well with little or no frost burn.
Lithodora grows and flowers best when planted in full sun. However, I have planted them in part sun and shade and they seem to just fine. If planted in a location that is too shady the plants tend to get a little leggy and may need shearing to maintain an attractive appearance.
If pruning is needed, the best time to prune or shear them is immediately after the plant has finished flowering, in late June or early July. If any leggy or spindly growth should develop, during the growing season, simply shear it back.
Since Lithodora is grown in containers, they are easy to transplant, even when the plants are in full bloom. Simply, water them thoroughly, remove the plants with soil intact, and set them into the new planting soil, making certain they are planted at the same depth as they were planted in the container. Prepare the planting soil by mixing compost, peat moss or processed manure with your existing soil. The soil must be well drained.
If soil preparation is done properly the plants will seldom need feeding. However, if the foliage does turn an off-color greenish yellow indicating the need for feeding, use a rhododendron type acid fertilizer to feed them. The best time to fertilize is in late winter or earliest spring.
If you have an established plant that needs to be relocated, the best time to transplant it would be during the winter dormant season months of November to March. Do the transplanting at a time when the ground is not frozen. Remember the plant must be moved with soil attached to the root system, as they will not successfully transplant bare-root.
'Grace Ward' and 'Heavenly Blue' are the two varieties that are most readily available. However, in recent years, the varieties 'White Swan' and 'Star' have been offered by some specialty nurseries. Both are still a bit difficult to find. 'White Swan' has white flowers, while 'Star' is blue with a white margin on the edges of the flower petals.
Lithodora can be propagated by seed, started indoors in either March or April. Cuttings of mature new tip growth can be taken from established plants in July or August.