Learn About Coleus
How to Sow
Coleus may be grown from seed sown early indoors and transplanted outside after frost, or from potted plants.
Sowing Seed Indoors:
- Sow indoors 6-8 weeks before last frost using a seed starting kit.
- Sow sees shallowly lightly covered with fine seed starting soil.
- Keep the soil moist at 65-85 degrees. Coleus can benefit with bottom heat.
- Seedlings emerge in 12-21 days.
- As soon as seedlings emerge, provide 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. Incandescent bulbs will not work for this process because they will get too hot. Most plants require a dark period to grow, do not leave lights on for 24 hours.
- Thin to one seedling per cell when they have two sets of leaves.
- 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.
- Transplant hardened-off seedlings to the garden after the frost.
- Before planting in the garden, seedling plants need to be “hardened off”. 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.
Planting Potted Plants in the Garden:
- Select a location in full to part shade with good rich well-drained organic soil protected from wind.
- Prepare the bed by turning the soil under to a depth of 8 inches. Level with a rake to remove clumps of grass and stones.
- Most plants respond well to soils amended with organic matter. Compost is a wonderful form of organic matter with a good balance of nutrients and an ideal pH level, it can be added to your planting area at any time. If compost is not available, top dress the soil after planting with 1-2 inches of organic mulch, which will begin to breakdown into compost. After the growing season, a soil test will indicate what soil amendments are needed for the following season.
- Plants should stand 12 inches apart in the garden.
- Dig a hole for each plant large enough to amply accommodate the root ball.
- Set level with the surrounding soil. Fill with soil to the top of the root ball. Press soil down firmly with your hand leaving a slight depression around the plant to hold water.
- Water thoroughly, so that a puddle forms in the saucer you have created. This settles the plants in, drives out air pockets and results in good root-to-soil contact.
- Use the plant tag as a location marker.
How to Grow
- 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 also 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.
- Keep plants well-watered during the coleus growing season, especially during dry spells. Plants need about 1 inch of rain per week during the growing season. Use a rain gauge to check to see if you need to add water. It's best to water with a drip or trickle system that delivers water at low pressure at the soil level. If you water with overhead sprinklers, water early in the day so the foliage has time to dry off before evening, to minimize disease problems. Keep the soil moist but not saturated.
- Until plants become established, some protection from extreme winds and direct, hot sunlight may be necessary. Good air movement is also important.
- After new growth appears, a light fertilizer may be applied. Keep granular fertilizers away from the plant crown and foliage to avoid burn injury. Use low rates of a slow release fertilizer, as higher rates may encourage root rots.
- Pinch flower stalks off before they bloom as they can detract from the foliage display.
- Pinch stem tips just above a leaf pair to keep plants maintain their compact, bushy habit.
- Monitor coleus plants for pests and diseases. Check with your local Cooperative Extension Service for pest controls recommended for your area.
- Remove plants after they are killed by frost in fall to avoid disease issues the following year.
- Coleus also makes a fine house plant. Bring smaller plants indoors before the last frost.
- Coleus plants are extremely easy to grow from cuttings. Choose a vigorous-looking stem tip, and cut off a 3-4 inch piece just below a leaf joint. Pull off the bottom set of leaves and place the cuttings in a glass of water, with its leaves resting on the edge of the glass and the stem in the water. Roots should appear in a week or two. Allow several roots to grow before transplanting. Check water daily to make sure stem is underwater, and replace it with fresh water every couple of days.
- Coleus is great for window boxes, pots, hanging baskets, and patio containers in partially shaded areas. Established plants are ideal for children to grow.
Annual Flower Growing Tips
Common Pests and Problems
Common Disease Problems
Damping Off: This is one of the most common problems when starting plants from seed. The seedling emerges and appears healthy; then it suddenly wilts and dies for no obvious reason. Damping off is caused by a fungus that is active when there is abundant moisture and soils and air temperatures are above 68 degrees F. Typically, this indicates that the soil is too wet or contains high amounts of nitrogen fertilizer. Burpee Recommends: Keep seedlings moist but do not overwater; avoid over-fertilizing your seedlings; thin out seedlings to avoid overcrowding; make sure the plants are getting good air circulation; if you plant in containers, thoroughly wash them in soapy water and rinse in a ten per cent bleach solution after use.
Downy Mildew: This fungus causes whitish gray patches on the undersides and eventually both sides of the leaves. Burpee Recommends: Do not plant in the same area for several years. Avoid overhead watering. Provide adequate air circulation, do not overcrowd plants. Do not work around plants when they are wet.
Powdery Mildew: This fungus disease occurs on the top of the leaves in humid weather conditions. The leaves appear to have a whitish or greyish surface and may curl. Burpee Recommends: Avoid powdery mildew by providing good air circulation for the plants by good spacing and pruning. Contact your Cooperative Extension Service for fungicide recommendations.
Root Knot Nematodes: Microscopic worm-like pests that cause swellings (galls) to form on roots. Plants may wilt or appear stunted. This is a serious problem in many Southern states. Burpee Recommends: Do not plant into infested soil. Grow resistant varieties. Try planting ‘Nema-Gone’ marigolds around your plants.
Root Rots: A number of pathogens cause root rots of seedlings as well as mature roots. Burpee Recommends: Practice crop rotation and do not plant related crops in the same area for several years. Pull up and discard infected plants. Make sure your soil has excellent drainage. Contact your Cooperative Extension Service for recommendations.
Common Pest and Cultural Problems
Aphids: Greenish, red, black or peach colored sucking insects that can spread disease as they feed on the undersides of leaves. They leave a sticky residue on foliage that attracts ants. Burpee Recommends: Introduce or attract natural predators into your garden such as lady beetles and wasps who feed on aphids. You can also wash them off with a strong spray, or use an insecticidal soap.
Mealybugs: Mealybugs are 1/8 to ¼ inch long flat wingless insects that secrete a white powder that forms a waxy shell that protects them. They form cottony looking masses on stems, branches and leaves. They suck the juices from leaves and stems and cause weak growth. They also attract ants with the honeydew they excrete, and the honeydew can grow a black sooty mold on it as well. Burpee Recommends: Wash affected plant parts and try to rub the bugs off. They may also be controlled by predator insects such as lacewings, ladybugs and parasitic wasps. Check with your Cooperative Extension Service for pesticide recommendations.
Slugs: These pests leave large holes in the foliage or eat leaves entirely. They leave a slime trail, feed at night and are mostly a problem in damp weather. Burpee Recommends: Hand pick, at night if possible. You can try attracting the slugs to traps either using cornmeal or beer. For a beer trap, dig a hole in the ground and place a large cup or bowl into the hole; use something that has steep sides so that the slugs can’t crawl back out when they’re finished. Fill the bowl about ¾ of the way full with beer, and let it sit overnight. In the morning, the bowl should be full of drowned slugs that can be dumped out for the birds to eat. For a cornmeal trap, put a tablespoon or two of cornmeal in a jar and put it on its side near the plants. Slugs are attracted to the scent but they cannot digest it and it will kill them. You can also try placing a barrier around your plants of diatomaceous earth or even coffee grounds. They cannot crawl over these.
Spider Mites: These tiny spider-like pests are about the size of a grain of pepper. They may be red, black, brown or yellow. They suck on the plant juices removing chlorophyll and injecting toxins which cause white dots on the foliage. There is often webbing visible on the plant. They cause the foliage to turn yellow and become dry and stippled. They multiply quickly and thrive in dry conditions. Burpee Recommends: Spider mites may be controlled with a forceful spray every other day. Try hot pepper wax or insecticidal soap. Check with your Cooperative Extension Service for miticide recommendations.
Sunscald: Leaves are bleached and faded, often turn white with brown crispy edges. There are no signs of pests and diseases. Plants were usually recently moved. The bright light and heat from the sun break down the chlorophyll which leads to death of the leaf. Burpee Recommends: Transplant coleus to a spot that has more shade in the afternoon. Do not place coleus in a south or south-west exposure.
Can you tell me why my coleus has suddenly dropped its leaves? Coleus is very sensitive to cold and frost. Do not plant out until all danger of frost has passed.
Can I over winter coleus as a houseplant in the winter? Yes, keep it in a window with morning sun. It is normal for it to drop leaves when first moved. If you find the edges of the leaves turn brown it is usually due to low humidity. Place the pots on a tray of damp pebbles.
My coleus just starting spouting and the leaves are just green should I be worried? No it is normal for the young leaves to be just green. Once the plant is outside in the shade the color will become vibrant.
Can coleus take the sun? Coleus is primarily a shade plant and can experience sunscald and wilt in full sun. In nature coleus is an understory plant. The ideal conditions are morning sun and protection from afternoon sun.
Why should I cut the flowers off? The flowers take strength from the plant and are often thought of as unsightly with the colorful foliage. But if you like the flowers you can keep them, just deadhead so they do not go to seed.