January 2004
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Garden design using shade plants and shade trees   

Gardening Newsletter - January 2004, Issue 17

A reader recently wrote to us asking for some tips on starting plants by seed. It instantly struck me that a lot of our readers are probably starting their summer flowers by seed right now. As such, I decided to devote this newsletter to the subject.

Unfortunately, every type of seed has its own set of ideal conditions for germinating. There are no ‘one size fits all’ types of recommendations I can give you. As such, I am writing individually about some of the most popular shade loving annual flowers and how to start them from seed.

Happy planting!

Rebecca Green
Horticulturist

Shade Loving Annuals and How to Start Them From Seed

Antirrhinum majus – commonly called snapdragon

Antirrhinum majusSnapdragons are always a favorite. Children love to pinch open the two-lipped flowers and watch them close. Apparently even the Romans did this, for they called the plant lion’s snap. The old English called it dragon’s snap, which evolved into snapdragons.

The botanical name for snapdragons, Antirrhinum majus, refers to the flower's snout-like shape. The word anti means like and the word rhin means snout or nose.

As playful as these flowers may be, they are not as innocent as they look. They are in the same family of plants as Digitalis (foxglove), the Scrophulariaceae family. Hence, snapdragons may very well contain some of the same poisons as Digitalis. The deer certainly don't eat it.

Snapdragons are very prone to damping off, a fungus disease. For this reason it is best to start the seeds in a sterile potting medium, such as perlite. The seeds should be sown thinly. Make sure there is adequate air circulation around the seedlings. Keep the foliage dry by watering from the bottom.

Plant young plants in full sun or light shade in well drained soil. Tall varieties should be planted twelve inches apart and may need to be staked. They should be kept out of the wind. Dwarf plants should be planted six to eight inches apart.

To make the plants grow bushy pinch the tips of the plants off when they are young. Regular deadheading, removal of spent flowers, will keep them blooming all season. Snapdragons are always a favorite.

Many people don’t realize snapdragons come in different heights. There are dwarf cultivars, which are good as bedding plants. Intermediate height plants make good cut flowers. The tallest varieties can be used in the back of the border.

Begonia semperflorens-cultorum – commonly called wax begonia

Begonia semperflorens-cultorumTheir low growing habit make waxed begonia a popular bedding plant. They are also frequently used in window boxes and planters.

In addition to cheery flowers, wax begonias have attractive succulent foliage. Some even have foliage in unusual colors. There are a group of begonias called the Cocktail series that have bronze colored leaves.

Wax begonias are very prone to fungal diseases, such as: damping off, botrytis, and stem rot. Consequently, it is a good idea to plant the seeds in perlite. When the young plants are transplanted to the outside or to pots, well-drained soil will help prevent these diseases. Plants grown in the shade are also prone to slugs.

Plants need to be started from seed indoors fifteen to twenty weeks prior to being transplanted outdoors. For this reason many prefer to purchase young plants rather than start out with seed.

Begonia tuberhybrida – tuberous begonia

Begonia tuberhybridaI love tuberous begonias. Their flowers remind me of tiny roses. They can be used in planting beds or in planters. I created a wonderful planter one year using tuberous begonia and coleus.

The roots of tuberous begonias are somewhat similar to a bulb, and are called tubers. You can store the tubers in a cool dry place over the winter or purchase new tubers every spring. While they can be started from seed, it is usually best to grow these plants from tubers.

If you want to keep your tubers from one year to the next they should be gently dug-up from the ground after the first frost. Wash them off in clear cool water and let them dry in the sun. They should be stored at a temperature of forty to forty-five degrees. Periodically check them for rot and discard any that may be decaying.

If you want your tuberous begonias to bloom in the summer plant them directly outdoors as soon as the soil has warmed. If you want you plants to bloom sooner, start your tubers indoors six to twelve weeks before blooming. Use a loose, fluffy growing medium and don’t plant them too close together. The concave side of the tuber should be facing up.

Caladium x hortulanum – commonly called fancy-leaved caladium

Caladium x hortulanumCaladiums are beautiful, exotic and, fascinating plants. Natives of South America and members of the Arum family (Araceae), they are grown as annuals in most of the United States. If the temperature of their environment dips below 65 degrees F they will die. However, if their tuberous roots are dug-up in the fall and stored in a cool dry place over the winter, they may be replanted in the spring.

The name Caladium is a Latin version of the plant's Amazon River name, kaladi.

Caladiums contain calcium oxalate crystals that cause severe burning of the mouth. These microscopic crystals can irritate the skin and eyes too upon contact. While capable of inflicting great pain, Caladiums are not lethal.

Caladium's flowers are not that impressive. They consist of a fleshy spike with a showy bract. After flowering they get white berries.

Caladiums are grown primarily for their beautiful leaves. Large and heart shaped, they are frequently splashed with red, pink or white. There is even a Caladium with white leaves and green veins called Caladium x hortulanum.

In all but the warmest parts of the country Calidiums should be started indoors in April. Plant the tubers with the eyes facing downward in a mixture of peat and sand, and keep them at a temperature between 75 degrees F and 85 degrees F. To have a bushier plant, remove the largest eye with a knife before planting, this will cause the smaller eyes to grow more. When shoots emerge transplant them into rich soil. However, don’t plant them outside until the nighttime temperatures are between 65 and 75 degrees F.

To carry plants over from one gardening year to the next, dig the plants up in the fall and plant them in a container. Bring them indoors and gradually decrease the amount of water they receive. When the leaves turn yellow and drop off dig up the tubers and store them in a mixture of dry peat, sand, and perlite. Store the tubers at a temperature of sixty to sixty-five degrees F in a dry spot.

Coleus hybrids – commonly called coleus

ColeusAlthough this plant is a perennial in the tropics, throughout most of the United States it is used as an annual. It is also frequently used as a houseplant.

In response to the soaring popularity of Coleus, growers have developed a myriad of wonderful new cultivars. It use to be that Coleus could only be grown in the shade. Now most of the Coleus that are for sale can be grown in either full sun or partial shade. Today you can find a Coleus that will grow in all but the wettest of soil.

Coleus is in the family Lamiaceae, which is the mint family. Deer despise virtually every plant in this family. Other members of the Lamiaceae family are lavender (Lavendula species) and catmint (Nepeta species). All plants in this family have square stems.

The colorful leaves of this plant make it a wonderful addition to the garden. The leaves are mottled with shades of red, pink, white, green and purple.

Although coleus does get a small light blue flower, it is really insignificant. In fact, it is best to pinch the flower buds off. This keeps the plant much denser. If left to flower, coleus can become leggy.

If you use this plant as an annual, especially in a container, fertilize it heavily. If it is in a container you should add some perlite to your soil to help hold the moisture. Do not allow it to dry out. Unlike some of its relatives in the Lamicaceae family, coleus is not drought tolerant.

Impatiens spp. – commonly called New Guinea impatiens

New Guinea impatiensSo many people automatically think of impatiens when they think of shade loving flowers. However, they take varying amounts of sunlight. During the fall and spring in the South they can withstand full sun or light shade. Likewise, if the climate is cool and/or cloudy they can take full sun. There are even a few varieties that need full sun. However, the sun lovers shouldn’t be planted in the South because the sun there is too intense. Nevertheless, it is true that in most of the country most impatiens need shade, especially in the South in the summer.

While they don’t like soggy soil, impatiens do need moisture. Planted them in soil that has lots of organic matter that holds the moisture.

The flowers come in just about every hue and some even have colorful foliage. They are excellent for flowerbeds as well as planters and window boxes.

There are different types of impatiens from different parts of the world. However, the ones with the prettiest flowers and most often used in American landscapes are New Guinea impatiens.

The name impatiens comes from the Latin word for impatient. Perhaps this is due to the way they disperse their seeds. When a ripe seed capsule is touched it explodes, spraying the seeds everywhere.

Impatiens can be started from seeds or stem cuttings. Some seeds will germinate in ten to fourteen days indoors if kept at seventy-eight to eighty degrees. They should be sown fourteen to sixteen weeks before the last frost. Cuttings should be taken in the spring or summer. Stick the bottom of the cutting in sand, perlite, or vermiculite. A heat source should be beneath the planter at a temperature of seventy-five degrees. The planter should be enclosed in plastic.

Lobelia erinus – commonly called edging lobelia

Lobelia erinusLobelia makes wonderful edging plants. They are quick growers with a neat, compact habit. It also looks great cascading over the edge of a container.

Like a lot of plants, how much shade lobelia requires depends on where you grow it. In the South they absolutely must have partial shade and need to be sheared back after blooming. However, in the North they can tolerate full sun.

Starting lobelia from seed is tricky. The seedlings are prone to damping off, a fungus disease. Therefore the seeds should be planted in a sterile medium, such as perlite, and drenched with a fungicide. The seedlings are also sensitive to being transplanted. Therefore plant a few seeds together in a small container. When the seedlings are ready to be transplanted just tap the bottom of the container and plant all the contents, soil and seedlings, into the ground.

Nicotiana spp. – commonly called flowering tobacco

NicotianaThere are many types of Nicotiana, commonly known as flowering tobacco. Nicotiana x sanderae and Nicotiana sylvestris are the two most popular decorative tobaccos, and are the subject of this discussion.

Both Nicotiana x sanderae and Nicotiana sylvestris are closely related to the plant that produces smoking and chewing tobacco, Nicotiana tabacum. Sir Water Raleigh introduced nicotiana tabacum to Great Britain in 1570. The name Nicotiana commemorates Jean Nicot, the man who brought tobacco seeds to France.

Nicotiana x sanderae is sometimes called the short flowering tobacco, reaching a height between 12 inches and 2 feet tall. Sometimes it is mistakenly called Nicotiana alata. The fragrance varies with the cultivar. Some are sweet and others have no noticeable scent. The flowers have five petals resembling a star shape. They come in shades of white, pink and, pale green.

If Nicotiana x sanderae is the short flowering tobacco, then Nicotiana sylvestris is the tall flowering tobacco, native to Argentine. Nicotiana sylvestris may reach 5 feet in height. It has large leaves and drooping clusters of white flowers that are very fragrant at night. It readily self-sows if not deadheaded. In the very southern portion of the U.S. it is perennial. Plant it in a protected area so that the wind does not damage the large leaves or tall flowers.

Nicotiana x sanderae do well in either full sun or partial shade. However, the flowers do better in partial shade. This is especially true in hot climates.

Nicotiana sylvestris is more adaptable, doing equally well in sun or partial shade. However, aphids may be a problem in the shade.

Sow Nicotiana x sanderae seed eight to ten weeks before the last frost date. There is no need to cover the seed. When kept at seventy degrees F, germination occurs in seven to twelve weeks. Reduce the temperature to sixty degrees once the seeds have become seedlings.

The process is a little different for Nicotiana sylvestris. Sow seeds indoors four to six weeks prior to the last frost. Do not cover the seeds. Germination will take place in seven to twelve days when kept at seventy degrees.

Both types of Nicotiana need fastidious deadheading, removing of spent flowers.

Short nicotiana looks good planted in masses between shrubs and in flowerbeds. Individual plants don't make a very bold statement. They also are attractive in container plantings.

Tall nicotiana should be used in the back of a bed due to its height. It is a very bold plant, making a strong statement in the garden.

Viola x wittrockiana – commonly called garden pansy

Viola x wittrockianaPansies are known to withstand frost, letting you plant them in your beds earlier than most annuals. They can be massed around tall tulips to create a layered effect. They are great in perennial borders, where they provide welcome color before the perennials come into bloom. Pansies are also great in containers. They even can be eaten, their petals used to decorate elegant dishes and salads.

However, a lot of people don’t realize that their cold hardiness also makes them great for fall plantings too, especially in the South. Black and orange pansies make a wonderful Halloween display. In the Deep South they can be used in winter plantings.

The name pansy comes from the French word perisee, which means thought. It was believed that the violet and its child the pansy induced contemplation.

Pansy’s come in a myriad of colors. Most people don’t realize how diverse pansies can be since garden centers usually only carry a few popular varieties. The gardener who starts his/her own plants by seed is greatly rewarded by the fabulous plants they grow.

Pansies are a little unusual in that the seeds need to be sown in the fall to have flowers in the spring. They can be sown outside in a lightly shaded area in August and transplanted to where you want them to grow in September. Alternatively you can sow them indoors in late October. In this case the seeds need to be covered and placed in total darkness. Keep the planter at sixty-five to seventy degrees F and germination will take place in six to twelve days. The seedlings should then be kept in a cold frame or greenhouse until the spring when they are planted outdoors.

Pansies are very adaptable plants. They will grow in almost any type of soil in full sun or partial shade. However, they grow best in rich, well-drained soil, in partial shade. Not only do they fade in full sun, but also the flowers don’t last as long. Deadheading will also help your blooms to last longer.

Pansies are prone to slugs and aphids

That's all for now. If you have any comments or questions on the newsletter, please email us at

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Last modified: February 08, 2004