Nasturtium: Indoor or Direct Sow or Potted Plant Annual
How to Sow and Plant
Nasturtium may be grown from seed sown early indoors and transplanted outside after frost, or sown directly in the garden after frost, or grown from potted plants.
Note: When sowing from seed, before sowing, gently rub the seed with a nail file to aid germination, as nasturtium has a hard seed coat.
Sowing Seed Indoors:
- Sow indoors 4-6 weeks before the last frost using a seed starting kit. It is best to use a large celled kit, or fiber pots as nasturtium roots are easily damaged when transplanting.
- Sow seeds ½ inch deep in seed starting soil
- Keep the soil moist at 70-75 degrees
- Seedlings emerge in 10-14 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.
- 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.
Sowing Directly in the Garden
- Direct sow seeds in average soil in full sun after all danger of frost.
- 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.
- Sow seeds ½ inch deep 12 inches apart.
- Firm soil lightly, water and keep evenly moist.
- Seedlings will emerge in 10-14 days.
Planting Potted Plants:
- Select a location in full sun with moist, well drained organic soil.
- 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.
- 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. Be careful to not disturb the roots as nasturtiums can resent being transplanting.
- 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 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.
- Do not over fertilize as nasturtiums prefer a poor soil.
- Climbing varieties will need some training and support on their upward journey.
- Deadhead to keep plants flowering longer.
- 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
- Nasturtiums do best in areas with relatively cool summers, but usually, they can grow anywhere.
- Nasturtiums cut for vases often root in water.
- Nasturtiums are pretty annuals to use as edgings or at the front of a flower bed with other low-growing annuals and perennials. Allow plants to trail over walls or raised beds, and use them to add summertime color to rock gardens. They also look beautiful in containers and window boxes.
Common Disease Problems
Aster Yellows: Plants are stunted, may develop witch's brooms (excessive growth), petals turn green and become deformed. This virus-like condition is spread by leafhoppers. Burpee Recommends: Remove infected plants and control leafhoppers. Remove weeds in the area which serve as alternate hosts to the disease.
Bacterial Leaf Spot: First signs are small translucent spots with a broad yellowish edge that slowly enlarge and become angular or irregularly circular with a reddish center. It thrives in cooler temperatures. The disease may also affect and disfigure flower heads. Burpee Recommends: Remove infected plants. Rotate crops with plants in a different family. Avoid overhead watering. Do not work around plants when they are wet.
Clubroot: Leaf symptoms include stunting, yellowing and wilt. When the plants are removed from the soil, the roots may have galls, swelling or be distorted. Burpee Recommends: Test the soil pH as clubroot is most common in acid soil. Add lime to raise the pH. Avoid planting where brassica plants were grown the previous year.
Fasciation: Fasciation is an abnormal flatting of stems, which may cause them to have a fused appearance. Distortion often develops at the base of the plant. It is usually caused by a bacteria or virus and enters through a wound in the plant. Burpee Recommends: Be very careful when handling plants. Remove and destroy any plants that show signs of the disease.
Nasturtium Mosaic Virus: The most characteristic sign of this virus is tight and dark green mottling of the leaves. Flowers may be deformed, streaked or faded. It can be transmitted by aphids and leafhoppers. Burpee Recommends: Remove and destroy plants monitor and treat for infestations of vector insects.
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. Nasturtiums are sometimes used as trap plants to lure aphids away from other plants. 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.
Cabbage Looper: These worms are green with a white stripe on either side, about 1-1.5 inches long. Burpee Recommends: Hand pick. Floating row covers can help prevent their laying eggs on the plants.
Leafhoppers: Leafhoppers cause injury to leaves and stunt growth. They also spread disease. Burpee Recommends: Remove plant debris. Use insecticidal soaps. Consult your Cooperative Extension Service for other insecticide recommendations.
Leafminers: These insects bore just under the leaf surface causing irregular serpentine lines. The larvae are yellow cylindrical maggots and the adults are small black and yellow flies. They do not usually kill plants, but disfigure the foliage. Burpee Recommends: Remove affected foliage.
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.
Nasturtiums FAQs
Are the flowers edible? Yes flowers have a peppery taste and are used to garnish salads or other dishes. Young leaves have a flavor like watercress and are good in salads.
Why didn’t my nasturtiums flower? Nasturtiums like a poor soil so be very careful not to over fertilize the plants. The result is pretty plants but no flowers.
Why didn’t my seeds germinate? Nasturtiums have a thick seed coat and should be filed with a nail file before sowing to aid in germination.
Do nasturtiums attract pollinators to my garden? Yes nasturtiums attract bees, butterflies and hummingbirds to the garden.
What plants will benefit from using nasturtiums as a companion plant? Nasturtiums make a good companion for: broccoli, Brussels sprouts, cabbage, cauliflower, cucumbers, kale, kohlrabi, pumpkins, radish, squash, tomato, and potato.