How to Plant & Grow Marsh Obedient Plant (Physostegia leptophylla)


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Marsh obedient plant in bloom with purple flowers
Marsh obedient plant produces beautiful lavender-colored blooms every summer. Michael Wolf, Penig, CC BY-SA 3.0, via Wikimedia Commons

Physostegia leptophylla is a showy perennial herb that is commonly known as slenderleaf false dragonhead or marsh obedient plant. This attractive species falls under the Lamiaceae family, which includes important culinary herbs such as mint, sage, and rosemary. One of 12 species of the Physostegia genus, this obedient plant is native to the marshlands of Eastern United States, where it produces gorgeous bouquets of pastel blooms every summer! Its flowers are remarkably similar to those of the Dracocephalum genus, which are collectively referred to as the true dragonheads.

Evidently showy, the marsh obedient plant is far from modest and grows up to 4 feet (121 cm) tall. Its bright green fronds arise in opposing pairs around a quadrangular stem. The lowermost leaves tend to have longer petioles compared to the uppermost leaves, which can appear to hug the stem. These leaves have either undulating margins or have a toothed, yet rounded, edge. These features distinguish this species from other obedient plants occupying the same native range (P. virginiana, P. purpurea).

Erupting from terminal racemes, the obedient plant’s tubular flowers are near-impossible to miss! The petals are deep to light lavender, with striking splotches of purple at their interiors. They also have a downy texture due to the presence of fine hairs that grow to just 0.1 mm long.

Facts, Benefits & Uses of Marsh Obedient Plant

With water-loving roots and rhizomes, the marsh obedient plant’s vertical spikes can attract a host of pollinators to the margins of your pond. Once pollinated, each flower can produce up to 4 fruits, which appear to be tiny angular-shelled nuts. In the wild, this plant is found in the shallows of river openings and along the margins of marshes. They can even thrive in the brackish waters of tidal zones.

Obedient plants have earned their common name from the way their flowers are oriented – bending in all directions. Flowers can be forced to face another direction, and they surprisingly stay in place instead of bouncing back to their original orientation. Based on growth habits, however, they are generally disobedient and will rapidly spread via their rhizomes in rich soil! If you’d like to grow this bog plant in your pond or water garden, do consider cultivating them in pots to restrict their spread.

Unfortunately, the status of this species is in decline, and it is now listed as a threatened plant under the Preservation of Native Flora of Florida Act. Loss of its natural habitat is attributed to wetland draining and conversion to agricultural land.

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Marsh Obedient Plant Fact Sheet:
PLANT TYPE
Aquatic herbaceous perennial
HARDINESS ZONES
USDA 5 – 11
LIGHT REQUIREMENTS
Full sun to partial shade
BLOOM COLOR
Lavender
BLOOM PERIOD
April to August
MAXIMUM GROWTH
5 feet (152 cm)
PLANTING DEPTH
4 – 10 cm (1.6 – 4 inches)
WATER QUALITY
pH 6.5 – 7.5

 


Marsh Obedient Plant Growth, Hardiness & Climate

Marsh obedient plant with purple flowers
Marsh obedient plant produces blooms through spring and summer and loses its foliage as winter approaches. Michael Wolf, Penig, CC BY-SA 3.0, via Wikimedia Commons

Physostegia leptophylla is fairly easy to grow and care for. It can withstand a wide range of growth conditions as it can thrive in USDA hardiness zones 5 – 11. A pond edge placement can provide its meager requirements, as it simply requires at least 2 inches of water, and can withstand freshwater to brackish environments. Optimal water temperatures range from 70 to 80 degrees Fahrenheit (21 – 27˚C).

This species can be cultivated in wet muck or peat, as these are generally its favored sediment types in the wild. It regularly produces blooms through spring and summer and will lose its foliage as winter approaches. You may consider growing it alongside evergreen marginal plants to ensure that your pond’s edges retain color all year round.

Do bear in mind that this plant can spread via rhizomes. If you wish to reduce its rate of spread, situate it in an area that receives less sun and withhold the use of fertilizer. Aquatic baskets or submerged containers may also effectively prevent rapid spread.


How to Plant Marsh Obedient Plant

Leaves of a marsh obedient plant
Be sure to remove any brown leaves to prevent excess organic decay in your pond. Krzysztof Ziarnek, Kenraiz, CC BY-SA 4.0, via Wikimedia Commons

Though commonly incorporated into ponds as mature, farm-raised plants, marsh obedient plant can be propagated via seed or rhizome division. Seeds will germinate on consistently moist soil, with a slightly acidic pH. Sow them onto shallow pots on a tray with a few centimeters of water. This should be done in a greenhouse or cold frame set-up to ensure that germination conditions are optimized. When the seedlings are large enough to handle, transplant them into individual pots.

Mature individuals can be transferred into your pond in spring. To ensure that the rhizomes don’t spread uncontrollably, it is advisable to use one-gallon containers or aquatic baskets. Submerge these at a level that provides at least 2 inches (5 cm) of water above the rim of the pot. Once the plants are established, they can be propagated by division in spring or summer. Carefully divide the rootstock or rhizomes, and plant them in a few inches of soil. Once new roots have developed and the divisions are established, they can be outplanted into your pond’s margins.


How to Care For Marsh Obedient Plant

To ensure that your plant blooms profusely, make sure it is located in an area that receives direct sun or medium shade. Avoid fluctuations of water depth that may occasionally expose the plant’s crown and rhizomes. Moreover, regularly check your pond water’s temperature and pH to ensure that proper conditions are provided. Marsh obedient plant prefers a slightly acidic to neutral pH level.

When undertaking routine pond maintenance, don’t forget to check this plant’s foliage for pests or diseases. Any affected parts, along with browning leaves and flowers, should be removed before they fully wilt to prevent excess organic decay in your pond. As this plant has an aquatic habit and can grow in poor soil, additional fertilizer is not required. If you’re interested in hastening its growth, you can bury fertilizer tablets into the submerged soil. Prior to purchasing the tablets, do ensure that they are safe for use in ponds with fish or wildlife.


How to Winter Marsh Obedient Plant

To prepare your marsh obedient plant for winter, remove leaves and stems that will begin to die off towards the end of autumn. If your plant is rooted directly into your pond’s margin, trim just enough foliage to leave about 1 – 2 inches (2.5 – 5 cm) of the plant above the waterline. If your plant is rooted into a movable pot or basket, the foliage should likewise be trimmed back prior to moving the pot deeper into your pond. This can then be left submerged for the duration of winter, particularly if the pond freezes over. Once the pond’s surface melts, you can return the pot to its marginal position. Growth should resume soon after.


Is Marsh Obedient Plant Invasive or Toxic?

Marsh obedient plant is not considered invasive. It is generally rare, even within its own native range. Due to the spreading rhizomes and self-fertilizing capacity of this plant, it would still be prudent to limit its growth if your garden or pond is located outside of Eastern North America. If you’re concerned about the spread of its seeds, you may cut its flowers before they develop into tiny nutlets.

Though there are no known toxins associated with obedient plants, they do have a special adaptation that serves as a form of defense against herbivory. Their leaves contain foliar idioblasts, which are essentially large oil-filled cells. The oil-filled leaves seem to effectively ward off grazers, such as deer, without the help of any poisonous compounds!


Is Marsh Obedient Plant Edible? Will Fish Eat it?

Marsh obedient plant isn’t exactly known for its edibility. The lack of toxins may render it safe for consumption, but its oil-rich leaves may produce an unappealing flavor or texture. For this reason, fish are not typically observed to consume its parts. In the event that curious pond inhabitants do partake in the plant’s leaves or seeds, you need not worry because this may simply be a one-time occurrence and enough to familiarize them with the plant’s non-palatable flavor.


Where to Buy Marsh Obedient Plant & Seeds? (UK & US)

Potted and farm-raised Physostegia leptophylla can be purchased from plant nurseries and aquascaping stores within its native range. As this plant is generally non-invasive, it may also be purchased via online plant portals. Make sure to purchase this plant from reputable stores, as it is considered threatened in the wild.

Additionally, remember to double-check the plant’s scientific name. Do bear in mind that there are other obedient plant species that look remarkably similar to this one but may not have the same aquatic preferences.

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