Horticulture is the art or practice of garden cultivation and management.
The Horticulture Committee stages workshops on all aspects of garden cultivation and management. Activities include tool care, seed harvesting and packaging, collaborating to host lectures, seed propagation, supporting the plant sale committee, preparing for PGC’s presence at GCA Horticulture Shows, and plant propagation.
What's Blooming Now
Dipsacus fullonom -- Wild teasel and Swallowtail Butterfly 2023
Thug of the Month - by Rosemary Ward
Garlic Mustard (Alliaria petiolata)
This ubiquitous plant is one of the leading contenders for “worst invasive” for its potential long-term impact, not only on forest ecosystems, but on the health of the trees themselves. A member of the Mustard family Brassicaceae, it is native to Europe, the UK and parts of Asia and was first recorded in the U.S. in the 1860’s when it was introduced for medicinal and culinary purposes! It’s extremely prolific and has of course since spread far and wide throughout the northeast and elsewhere.
It prefers semi-shade and is usually found in the understory or at the edges of the forest. A biennial, it’s one of the first plants to appear in early spring as a small leafy rosette. In its second year it grows larger and in early April produces a long flower stalk with a white cross-shaped flower at the end of and along the stalk. It is self-fertile and by the beginning of June is forming seed capsules which can produce thousands of seeds. These can remain viable for 5 years. Obviously it can crowd out other species but even worse, it’s allelopathic, meaning its roots release a toxin which disrupts the fungi or mycorrhizae in the soil and so impedes access to the nutrients which hardwood tree seedlings need to thrive. Studies have shown that trees in severely infested forests grow more slowly and in this way the long-term health of the forest can be seriously affected.
As if that weren’t enough, the leaves are toxic to butterfly larvae. Control is best achieved by hand-pulling before the seeds are dispersed and is quite easy at this stage, at least with small infestations. Deer and ground hogs tend to avoid it unfortunately.
As far as its culinary uses are concerned, it’s in the same family as broccoli, broccoli rabe and cabbage and is said to be delicious and nutritious! It can be used in salads and pesto if the leaves are from second-year plants growing in shade, which are less bitter. Otherwise they can be boiled for 7 - 10 minutes and sautéed with olive oil and garlic. The taproot is also edible and apparently tastes like horseradish. One caveat, if you think this might be a great way to achieve control, bear in mind that like other members of its family, it contains small amounts of cyanide and shouldn’t be consumed in large quantities - probably not more than twice a week. Bon appetit!
Wild Rosa Multiflora
The wild Rosa multiflora is native to E. Asia and was introduced in the 1880s for use in erosion control, as a rootstock and for livestock fencing. It has since naturalized throughout the Northeast and has become of the worst of all invasives. It’s a large shrub which forms impenetrable thickets, scrambles over shrubs and small trees engulfing them with its long arching canes, and will climb into trees up to a height of about 20’, depriving them of light. In June it produces large clusters of small white blooms and is a familiar sight in this area. The reddish-purple hips in the Fall are eaten by birds and spread far and wide.
The good news is that there is a natural control. This rose is a reservoir of a virus called Rose Rosette which is spread by a tiny wind-borne mite, and an infected plant will succumb in 2-4 years. It’s rapidly becoming established in this area.
The bad news for gardeners is that most garden roses are also susceptible to the virus. Symptoms of the disease include witches broom, elongated red shoots especially on the upper canes, excessive numbers of thorns and deformed chlorotic leaves. If you are vigilant and quickly cut off and destroy the infected canes you may be able to save the plant. (Don’t forget to disinfect your pruners.) If not, there is nothing to be done but to dig up and destroy it before it can infect other plants.
Mugwort - Artemesia vulgaris (Family Asteraceae)
Mugwort is one of many exotic plants which have escaped cultivation and in recent years become extremely invasive in North America. Japanese Knotweed (Polyganatum cuspidatum) and Black Swallowwort (Vincetoxicum nigrum) are other prime examples.
Artemisia vulgaris is native to Europe, Asia and Alaska. It is said to have been introduced by Jesuit priests for medicinal purposes - the suffix ‘wort’ was traditionally used to indicate a plant thought to have healing properties.
A tall herbaceous plant, 36” to 60”, with a characteristic pungent scent, it’s much in evidence along Philipstown roadsides these days, along with Japanese Knotweed. It flowers from July to September - however its flowers are insignificant. It spreads by horizontal rhizomes which form an extensive network and are very difficult to eradicate. Any part of a rhizome that remains in the soil will quickly regenerate. Mowing where feasible seems to be among the few options available.
Japanese Stiltgrass (Microstegium vimineum) is a warm season annual grass which is native to South and East Asia. Like so many exotic invasives, it was introduced accidentally, in this case as packing material for shipments of Chinese porcelain around 1919. It’s now found in about half the states in the US and is an all-too-familiar sight around here.
Its success is of course due to its adaptability, but it prefers warm and damp conditions and especially thrives in shade such as at the edge of woodlands. It forms rapidly-growing dense carpets of bright green leaves, 1-2’ tall , which crowd out other plants and also affect the chemistry of the soil by raising the pH. Obviously it’s extremely detrimental to native communities of plants and insects. Unfortunately it isn’t eaten by deer.
As the season progresses it becomes quite easy to pull out and so smaller areas can be managed, but large infestations are extremely difficult to eradicate. It’s crucial to prevent it from reproducing. It flowers in early Fall with an inconspicuous narrow spike (visible in the photo) and then dies back as the weather cools down. But if it’s allowed to set seed, the seedbank in the soil will remain viable for up to 7 years.
Stiltgrass does have however one positive and unexpected attribute. Even though it’s non-native, it serves as a host for native Satyr butterflies, some species of which are endangered. So if you’re feeling overwhelmed by acres of Stiltgrass, remember the butterflies!
Oriental Bittersweet (Celastrus orbiculatus)
I have chosen this plant because it’s easy to spot at this time of year with its persistent orange berries and twining growth habit. One of the most destructive of all the exotic invasives which threaten our native plant communities, it's rampant in this area. It’s a deciduous, dioecious woody vine which can reach 60’ into the canopy of tall trees or engulf smaller trees and shrubs, shading them out with its dense foliage. It climbs by wrapping itself tightly around the stems of its victims, thus eventually girdling them.
Like so many other problem plants, it was introduced as an ornamental in the 1860’s from Japan and China and having naturalized it's now found in many states east of the Rockies. Its success is due to its adaptability, rapid growth habit, shade tolerance and the fact that its otherwise insignificant flowers produce large quantities of showy orangey-red berries in the Fall, which persist into winter and are much loved by birds which disperse them far and wide. The seeds germinate readily and the young plants can grow in shade on the forest floor.
Without resorting to the usual herbicides, control can be achieved (with luck and effort) by cutting out the vines early in the season and then continuing to do so until the Fall. If this is done frequently the plant’s food reserves will eventually be exhausted. Small plants can pulled out easily but any part of the root system that remains in the soil will resprout.
There is a native bittersweet (Celastrus scandens) which is much less common and innocuous by comparison. You can tell them apart by the location of the flowers, in the axils of the stems in C. orbiculatus and terminally in C. scandens. The berries of the native plant are much less showy, less numerous and less attractive to birds. They are yellow as opposed to orange. Note that the skin of the berries of C. orbiculatus is also yellow at first, but when the fruit is ripe it splits to reveal the bright orange-red color. The biggest difference is their impact on the environment.
Sources for Information on Native Plants
search ecological systems for related plant communities, also: dec.ny.gov/animals/29392html, an on-line plant community book, and: acris.ny.nhp.org, New York Heritage Program of plant, animal & community guides
List of Pollinator Websites
Sources of Native Plants
Watch: The Beauty of Pollination