What Are Silver Dollar Plants and Where Do They Grow?
Botanically speaking, silver dollar plants are known as Lunaria annua (less frequently, but more accurately, as Lunaria biennis) and are classified as biennials. They are members of the mustard, or "cabbage" family (Brassicaceae). This makes them relatives of foods such as broccoli and Brussels sprouts.
Indigenous to western regions of Asia and to the southeastern part of Europe, silver dollar plants are suited to grow in planting zones 4 to 8. Aggressive spreaders due to their self-seeding abilities, they have become naturalized plants far beyond their native range.
Because they have a long taproot and do not transplant well, silver dollar plants are generally grown from seed. Sow the seeds outdoors in spring as soon as you can work the ground, cover them lightly with soil, and water.
Silver dollar plants grow to a height of 2 to 3 feet, with a spread about half of that. The foliage is heart-shaped, with scalloped leaf margins. As biennials, the foliage in their first year consists of a basal rosette of leaves.
But these biennials are grown not for their leaves, but for the flowers that come in the spring of their second year and for, even more so, what their flowers produce: the seed pods that eventually become the namesake "silver dollars." Technically, these seed pods are termed "silicles." The start of the blooming period, depending on where you live, will be in April or May.
Flowers are typically purple. The silicles start out green in color. This green is later sloughed off, along with the seeds. The fully dried seed pod that remains (which is actually just a see-through membrane) is an off-white color with a sheen that makes it shine like a coin (less often, the pods are purplish). These "silver dollars" are not perfectly round but, rather, oblong. A short, needle-like projection hangs down from the bottom of each seed pod. These glistening silicles are papery to the touch.
This biennial is listed as a non-poisonous plant by the Division of Agriculture and Natural Resources, University of California.
Growing Conditions, Uses, Care, and a Drawback
Grow silver dollar plants in a friable, deeply-cultivated soil (to accommodate their long taproots). They prefer a well-drained, humusy soil that stays (or, through irrigation, can be kept) evenly moist. Locate the plants in full sun to partial shade in the North. In the South, partial shade is preferable. Even in the North, there is an advantage to growing the plants in partial shade: You probably won't have to water them.
A classic use for the plants is in woodland gardens. Nor do you have to fuss over them: They will grow on their own in a neglected area of your landscaping as long as the conditions are right.
Although the flowers of silver dollar plants are attractive, the primary reason to grow these plants is for their novel seed pods. The pods can be used in dried floral arrangements, wreaths, etc. In fact, you do not even have to be proficient at crafts to use them: Simply insert a few dried bundles into a vase. They look terrific all on their own, with no work on your part. In fact, a favorite way to display them is simply to hang them from a hook over a window, so that the rays of the sun can shine through them.
A potential drawback in growing silver dollar plants is the ease with which they spread. Check with your county extension office before planting any to determine whether they are listed as invasive plants in your region (in which case they have the capability to crowd out native vegetation). As invasive plants go, though, silver dollar plants are hardly among the worst offenders.
Under the right growing conditions, one plant will eventually multiply into many plants. It is their ability to re-seed that makes them such aggressive spreaders. Their thuggish behavior will come as no surprise once you realize that they are related to dame's rocket (Hesperis matronalis), another invasive, which is also known as "sweet rocket" or "dame's gilliflower."
Because silver dollar plants spread by self-seeding, control is straightforward enough: Harvest the plants after their seed pods are fully developed but before they can drop any seed. In fact, this practice kills two birds with one stone, since you will want to harvest them, anyway, in order to use the attractive seed pods. Here's how:
When you're ready to harvest, cut off the plant at its base, bring it indoors, tie it off with some wire, twine, or string, and suspend it upside-down from a nail, hook, etc. in a room with low humidity. The seed pods should be fully dried in about 2 to 3 weeks under optimal conditions. The husk (which is the green, outer layer) often falls off by itself, but, if it doesn't, you can gently rub it off. Care for these plants consists essentially in harvesting them; they require little help from you to grow.
Origins of the Names
Silver dollar plants go by a number of other common names, including:
- Money plants
"Honesty" is the outlier here, in terms of understanding the derivation of the name. Most say it comes from the fact that you can see through the seed pods to the seeds within (as if the plants had nothing to hide and therefore were adopting an "open and honest" policy).
The origins of the other common names are more intuitive. "Money plant" continues with the coinage theme found in "silver dollar plant," an allusion to the shape and color of the dried seed pod. The pods have a rounded shape, bright color, and unusual shine.
"Moonwort," too, refers to the shape, color, and shine of these silicles, which are reminiscent of little moons. Of all the common names, this one is most in-line with the botanical name, because Lunaria means "pertaining to the moon." The suffix, -wort (pronounced as if it were spelled w-u-r-t), is from the Old English for "plant," so moonwort is literally "moon plant." Moonwort would be a natural for moon gardens.
Other examples of plants with common names that contain the -wort suffix are:
With all this talk of money and the -wort suffix, do not confuse this plant with moneywort (Lysimachia nummularia), better known as "creeping Jenny."