Mecardonia

( meh - kar - DOH - nee - uh )

At-A-Glance Information

This genus of delicate annual (or tender perennial) flowering plants is commonly called Axilflower, and includes species which need full sun and regular water. It is a slow-spreading groundcover plant that reaches up to 5 inches tall and 16 inches wide. Yellow flowers bloom from late spring through the first frost of the year. It is heat tolerant, being native to South America and the southeastern United States, but will only survive over winter if temperatures remain above 25 degrees Fahrenheit. These plants are ideal for hanging baskets, trailing over walls or containers, and for adding color to borders.

Mecardonia species and varietals

The genus Mecardonia is a member of the plant family Plantaginaceae and includes 12 species. Plants in this genus are related to Bacopa (Water Hyssop). The genus is named for Antonio Meca y Cardona, founder of the botanical gardens at the Barcelona Royal College of Surgery in 1784 and Spanish military officer. Mecardonia grows best in USDA hardiness zones 9a-11b or Sunset growing zones 3-24. To find your zone, click here: Zone Map.
Mecardonia spp. Hybrids and Cultivars (Mecardonia hybrida) (Hybrid Mecardonia)
​These plants are commonly grown as ornamentals in gardens, and have green foliage, reddish-green stems. Yellow flowers bloom from spring through fall. Plants are hardy down to 32 degrees Fahrenheit. Cultivars are listed below:
'Gold Dust'
'Goldflake'
'Little Sunshine'
'Magic Carpet'

Mecardonia procumbens (Bacopa procumbens) (Yellow-Flowered Waterhyssop, Baby Jump-Up, Metatera)
This species is native to tropical and subtropical regions of the Americas, and has naturalized in many warm regions around the globe. Flowers are small and yellow, borne at the end of stems. Leaves are green and stems are reddish. This species is considered invasive in India, Japan, Taiwan, Indonesia, northern Australia, and regions of Africa.

Caring for Mecardonia

Mecardonia plants can be purchased as starts from a reputable nursery or be grown from seed. They do well in areas of the garden that receive full sun; ideally they should be getting between 6 and 8 hours of sun each day for best growth rate and flowering. In the warmest areas, provide some late afternoon filtered shade when temperatures are at their peak. Install these plants in moderately rich, well-draining soil with a pH of between 5.5 and 6.5 (slightly acidic). If local soils are particularly poor in nutrients or do not drain well, make sure to amend the planting area with plenty of organic material before installing. Water newly planted Mecardonia regularly to help it develop a strong root system. At maturity, these plants appreciate consistently moist soil to avoid drought stress. Apply a layer of mulch around the planting area after installing to suppress weed growth, maintain consistent soil temperatures, and increase soil moisture retention.

Fertilize yearly in early springtime with an application of 2 inches of compost around the base of plants. Pull mulch back before applying, work the compost gently into the soil a bit, water it in, and then replace mulch. These plants are not heavy feeders, and this should be sufficient to provide the necessary nutrients for the active growing and flowering seasons. These plants are self-cleaning, which means that they do not need to be dead-headed. Like their relatives in the genus Bacopa, they shed their faded flowers regularly on their own. If plants get leggy due to too much shade or other growing issues late in the season, plants can be lightly cut back to encourage a bushier habit to emerge and encourage more growth and flowering. These groundcover plants can survive in the landscape for several years before needing to be replaced. They are grown as annuals outside of their preferred climate zones, pulled and composted at the end of the growing season and replaced in the next.

Propagation

​Mecardonia can be propagated either by using cuttings or from seed. To ensure that your propagated plant will have the exact same qualities and characteristics as the parent plant, use the cutting method. If you would like to experiment and see what plant you can grow from seed, just keep in mind that it will not necessarily be the same as the parent plant, especially if you are propagating a hybrid variety. Also, some hybrids may be sterile and will not produce seeds, so cuttings may be your only option in this case. To propagate your Yellow-Flowered Water Hyssop, follow the instructions below:

Propagating Mecardonia by Cutting
  1. Gather your materials. You'll need a clean, sanitized, sharp pair of garden shears, rooting hormone, a pencil, and a 3-inch pot filled with well-draining compost or other organic material. If you don't have any potting medium on hand, you can make some. Just mix together equal parts (by volume) peat moss and horticultural-grade sand or grit sand.
  2. In spring or early summertime, choose the plant that you'd like to propagate. Ensure that this plant has had a good watering the night before, as this will improve the chances your cutting will take root. Cut one or more 4-6 inch portion(s) of the end of a non-blooming branch and strip the leaves off of the lower half. Make a hole in your planting medium by pushing your pencil into the soil. Dip the end of the stem in rooting hormone, and plant it in your pot. Fill in soil around the cutting to support it, but do not pack it down too much.
  3. Moisten with water, and ensure that the pot has good drainage. Your pot should be kept in warm, sunny conditions indoors (and not in direct sunlight). Water whenever your soil is dry under the top layer. After about four to six weeks have passed, your cutting should be rooted. When you notice new growth, you'll know you have roots. 
  4. Keep your new plant in an area with bright light (though not direct sunlight) and temperatures between 55 and 70 degrees Fahrenheit. Ensure that the soil stays moist, but not wet, until the next spring, when you can transplant it to its new home. Ensure that the last frost of the year has occurred before doing this, as it can seriously damage your new shrub.

Propagating Mecardonia by Seed
  1. Keep in mind that the plant you get from seed will not necessarily mimic all of the characteristics of the parent plant. To propagate by seed, you will need a paper bag, a pot or tray filled with well-draining compost or other organic material, a spray bottle and a fork. The best potting medium for seed germination is a light blend of 1/3 pasteurized soil or compost, 1/3 sand, vermiculite or perlite, and 1/3 coconut coir or peat moss. 
  2. Harvest your seeds. The seed heads remain on plants where flowers once bloomed, and will become dry and turn light brown when seeds are mature. Once they have dried out and begun to split open, you can harvest the seeds. Cut them off of the plant, placing them in a paper bag. Harvest as many as you can, and place the paper bag in a dry, cool, dark area. They will begin to split open and release the seeds contained inside. Once they have been released, take them out of the bag and put them in a container so you can work with them.
  3. Water your prepared seed tray or pot filled with soil, and ensure that good drainage is occurring. Place your seeds in your prepared pot or seed tray about a quarter inch to a half-inch under the soil surface. Cover them with soil and water with your spray bottle. Place your tray of seeds in a warm area that receives bright, indirect light. A greenhouse is the most ideal climate, but a planting tray inside a window will do as well. Germination usually takes 7-14 days from sowing. Once you begin to see seedlings sprout and they are able to be handled, transplant them to their own individual 3-inch pots, filled with the same potting medium as described in Step 1. Loosen the seedlings from the potting medium by digging down with the tines of your fork about an inch and a half, gently working the seedling up until it is out. Then, replant the seedling in its individual pot.
  4. Keep the seedling's potting medium moist, but not wet, by spraying the soil with your spray bottle. Keep your new plant in an area with bright light (though not direct sunlight) and temperatures between 55 and 70 degrees Fahrenheit. Ensure that the soil stays moist, but not wet, until the next spring (after the danger of frost has passed), when you can transplant it to its new home.

Problems and Pests

Certain Mecardonia species are considered invasive in some regions; see the species descriptions above for more information. Check with local authorities before planting. Although Mecardonia plants are typically pest and disease resistant garden ornamentals, they can have issues with the following from time to time:
  • Spider Mites
  • Mealybugs
For more information on these pest and disease issues, including how to treat and prevent them, consult the following pages:

This Mecardonia has dried, browning growth underneath newer green foliage and flowers. Remove damaged growth and continue care.

Gallery

Mecardonia fronts a bed filled with orange and yellow Lantana as well as pink Globe Amaranth.
This multicolored bed features Petunia, Mecardonia, light green Sedum, dark-foliaged Amaranth, Gomphrena, and Feather Reed Grass.
Mecardonia is used as a small-space groundcover amongst taller shrublets in this front yard landscape.
These plants have trailing stems that present well in hanging baskets.
The yellow flowers of Mecardonia contrast nicely with pink-purple Petunia.
Mecardonia flowers resemble those of Nemesia species.
Here, Baby Jump-Up is used to fill in spaces between pavers in a walkway.
A garden escapee growing in disturbed, dry soil.
The specific epithet 'procumbens' refers to the fact that stems lay along the ground rather than stand upright.

Videos

Mecardonia is featured in this Plant of the Week video.
How to grow and care for Mecardonia plants.

Resources

Plant of the Week: Magic Carpet, Yellow
Growing Mecardonia
Wikipedia: Mecardonia
The New Sunset Western Garden Book: The Ultimate Gardening Guide (2012) - Page 438, Mecardonia 'Goldflake'