Bog sage is a perennial herbaceous shrub that is commonly used in gardens as an ornamental plant. It has lanceolate-shaped leaves that are covered in hair, and it produces blooms that display a stunningly bright shade of blue.
I. Appearance and Characteristics
The plant known as Salvia uliginosa, the bog sage, is a species of flowering plant in the family Lamiaceae, native to southern Brazil, Uruguay, and Argentina. It was described and named by botanist George Bentham for its typical habitat “of swamps and marshes”, or uliginosa.
Salvia uliginosa is an herbaceous perennial growing up to 3 to 6 feet (0.91 to 1.83 m) tall in one season, with multiple thin stems and yellow-green lance-shaped leaves that have serrated edges. The plant quickly spreads on underground runners and is readily divided.
The bright azure-blue flowers are .5 inches (1.3 cm) long with a white beeline in the throat pointing toward the nectar and pollen. They grow in whorls beginning in summer until fall, with many flowers coming into bloom at the same time.
Cyanosalvianin, the blue pigment from the flowers of S. uliginosa, is a metalloanthocyanin, a complex formed of six molecules of the anthocyanin type, six molecules of the flavone type and two magnesium ions.
Salvia uliginosa was introduced into horticulture in 1912, and has become popular in gardens and public landscapes for its azure-blue flowers, ability to grow under various conditions, and its pollinator habitat attributes.
This plant has gained the Royal Horticultural Society’s Award of Garden Merit.
II. How to Grow and Care
Sunlight
Salvia uliginosa require full sun, which is generally defined as a minimum of six hours of direct sunlight daily. There are varieties that will also tolerate partial shade. They are facultative long day plants and flower induction occurs more rapidly under long days. They will flower under any photoperiod, but will flower quicker and better under long days.
Until plants become established, some protection from extreme winds and direct, hot sunlight may be necessary. Good air movement is also important.
Temperature
Bog sage can grow in USDA zone 8-10. It grows best at the temperature of 16 – 19 °C. Once plants reach a saleable size, they can be moved to an open environment with good air movement. Plan ahead on this step because the plant grow very fast coming out of dormancy and can get leggy very quickly if grown too warm.
Watering
Bog sage are very drought tolerant and will do better in drier soil than overly moist soil. Lightly water when the top 2 inches of soil is dry. Keep the soil evenly moist during all stages of growing. The plants require average amounts of irrigation, and overly wet conditions will promote tall, leggy growth.
Soil
Bog sage prefers rich or clay soils. Drainage is also key and you should add grit to heavy or compact soils. If you are planting bog sage in a pot, the addition of perlite is recommended for better drainage.
Fertilizing
Salvia uliginosa are light feeders and only occasionally need fertilizer. A light application of a balanced fertilizer or compost in early spring, after new growth appears, can be sufficient. Keep granular fertilizers away from the plant crown and foliage to avoid burn injury. Use low rates of a slow release, as higher rates may encourage root rots.
Planting Instructions
The majority of bog sage species begin flowering in the summer and continue flowering all the way through to mid-autumn. When growing from seed, bog sage should be sown early in the growing season like spring to ensure that plants have time to establish themselves and flower before the arrival of frosts, later in the year. You can sow the seeds directly in the garden or, for early blooms, sow seeds indoors and transplant the new plants into the garden in early spring.
However, if you have bought a potted bog sage, you can choose to plant it either during the spring or the autumn. Although autumn may seem to be an unlikely time to plant bog sage, this is, in fact, a brilliant time of year for gardeners to get ahead before the next growing season. Autumn is an ideal time for planting or separating sage, not only to extend the flowering season in your garden but also to provide the plant with the opportunity to establish a healthy root system before its winter dormancy, so it is ready to burst into life the following spring.
Be sure to give bog sage plenty of space when positioning it in the garden, allowing for its tall and colorful blooms. If you are planting a tender variety of bog sage, such as Salvia coccinea ‘Lady in Red’, it may be better suited to a container that can be easily moved to a sheltered position, to avoid frost damage during the winter. In addition, gardeners in cooler regions may also like to consider treating tender varieties of bog sage that prefer warmer climates as annuals, rather than as typical perennials.
Pruning
Trimming and pinching can be done early when a fall planting is done. Pinching 2 to 4 weeks after transplant in the fall can assist in building a plant that has a thicker form and also give you more flowers spikes per pot. Trimming is not recommended when forcing plants in the spring or on plants that have been freshly planted in the spring from cooled liners.
Remove spent flower spikes to encourage flowering and prevent seed development. Pinching the growing tips of plants can encourage bushiness.
Mulching
Keep weeds under control during the growing season. Weeds compete with plants for water, space and nutrients, so control them by either cultivating often or use a mulch to prevent their seeds from germinating.
Mulches help retain soil moisture and maintain even soil temperatures. For annuals an organic mulch of shredded leaves lends a natural look to the bed and will improve the soil as it breaks down in time. Always keep mulches off a plant’s stems to prevent possible rot.
Propagation
Bog sage is usually propagated by seeds. Sow the seeds indoors 10-12 weeks before the last frost and keep evenly moist. Seedlings will emerge in 15-21 days at 21-24 °C. As soon as seedlings emerge, provide the temperature of 16-19 °C and plenty of light on a sunny windowsill or grow seedlings 3-4 inches beneath fluorescent plant lights turned on 16 hours per day, off for 8 hours at night. Raise the lights as the plants grow taller. Seedlings do not need much fertilizer, feed when they are 3-4 weeks old using a starter solution (half strength of a complete indoor houseplant food) according to manufacturer’s directions.
If you are growing in small cells, you may need to transplant the seedlings to 3 or 4 inch pots when seedlings have at least 2 pairs of true leaves before transplanting to the garden so they have enough room to develop strong roots. Before planting in the garden, accustom young plants to outdoor conditions by moving them to a sheltered place outside for a week. Be sure to protect them from wind and hot sun at first. If frost threatens at night, cover or bring containers indoors, then take them out again in the morning. This hardening off process toughens the plant’s cell structure and reduces transplant shock and scalding.
The plants can also be propagated by cuttings made in August or September, from vegetative (non-flowering) branches that are about 3 inches long. Remove the lower leaves and trim each cutting just below a node. You can either start propagating by placing them in water or by putting them in soil. If you opt for cutting propagation in water, just put the cuttings in a vase and add a few inches of water. When rooting cuttings in soil, dip the cut end in rooting hormone, then plant it in a moist potting medium. One good medium to try is a 70/30 mix of perlite/vermiculite and potting soil. After three weeks, the cuttings should be ready to pot on.
Pests and Diseases
The most common insect problem to watch for is the two-spotted Spider Mite. A routine scouting program is recommended to ensure that Whiteflies, Aphids and other greenhouse pests don’t harm the plant as well. Foliar diseases should also be scouted to prevent Botrytis and Crown Rots.
III. Uses and Benefits
Bog sage is an ideal addition to beds and borders.