Plectranthus: Indoor Sow Annual
How to Sow and Plant
Plectranthus may be grown from seed sown early indoors
Sowing Seed Indoors:
- Sow indoors 6-8 weeks before the last frost in spring using a seed starting kit
- Sow seeds shallowly in seed starting formula
- Keep the soil moist at 70-75 degrees F
- Seedlings emerge in 7-14 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.
- 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.
Transplanting in the Garden:
- Plant in the garden after all danger of frost has passed.
- Select a location in full sun in soil that drains well.
- 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.
- Dig a hole for each plant large enough to amply accommodate the root ball.
- Place the top of the root ball even with the level of 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.
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 soil evenly moist but not wet.
- 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 plants when young to encourage branching.
- Monitor 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.
Growing Tips
- Plants are grown mostly for foliage although they do bloom in late summer.
- Great for containers and as a contrast to flowering annuals in beds and borders.
- Tolerant of drought, heat and humidity once established.
- Foliage may be cut for arrangements.
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.
Leaf Spots: These can come from a number of fungus diseases, causing spots to occur on foliage. Burpee Recommends: Remove affected foliage and avoid getting water on the foliage when watering. Provide good air circulation. Contact your Cooperative Extension Service for fungicide recommendations.
Root Rots: A number of pathogens cause root rots of seedlings as well as mature roots. Burpee Recommends: 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 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.
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.
Whitefly: These are small white flying insects that often rise up in a cloud when plants are disturbed or brushed against. Burpee Recommends: They are difficult to control without chemicals. Try hot pepper wax or insecticidal soap. Check with your Cooperative Extension Service for pesticide recommendations.
Plectranthus FAQs
Can I grow plectranthus in a container? Yes, this is a perfect plant for a large container.
My plectranthus is toppling over, how can I prevent this? Pinch plants back when young to encourage branching. Be sure your plants are in full sun, do not over fertilize with a high nitrogen fertilizer.
Is plectranthus deer resistant? In general it does tend to be a deer resistant plant.
Is plectranthus a good pollinator plant? Yes, when it flowers it attracts butterflies and hummingbirds.