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Gardening Answers Knowledgebase

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I was looking at the Great Plant Picks list of recommended grasses, and I wonder why they exclude Carex, which I find is such a useful plant in the garden.


Great Plant Picks does in fact list two different Carex species but they are not on the list of grasses because Carex is a type of sedge, and sedges are not grasses. An article entitled "Sedges Have Edges" from Hilton Pond Center for Piedmont Natural History has a detailed explanation of the differences among grasses, sedges, and rushes. All three are graminoids, but grasses are in the Family Poaceae, sedges are Cyperaceae, and rushes are Juncaceae. According to the article, "a simple 'touch test' is the giveaway for sedges, whose stems when rotated have a very noticeable triangular shape--hence a total of three 'edges.'"


While reading a book on British woodlands, I came across a reference to a flower whose common name is 'town hall clock.' Can you tell me what plant it is, and why it has this name?


Townhall Clock's scientific name is Adoxa moschatellina, in the Adoxaceae family. Other common names for this native British wildflower are Moschatel, Five-Faced Bishop, Muskroot, Tuberous Crowfoot, and Hollowroot. All of those names are descriptive of various aspects of the plant's appearance, but the name Townhall Clock is evocative of the way this pale yellow-green early spring flower rises up on a slender stem. According to Sarah Raven (in her book Wild Flowers, Bloomsbury, 2012), four faces of the flower are "arranged as if on the surface of a cube, the fifth facing upwards." The aroma of the flowers is musky, or like "elder blossom with a bit of almond."

There are some detailed photos of it on this Finnish plant identification website. Despite the name Townhall Clock, it's a subtle flower that might easily be overlooked. In fact, its genus name means "without glory," due to its unshowy blooms.


My local nursery is selling bags of bat guano, and enriched compost that includes it. What is it good for, and is it safe to use? The company describes all their products as organic.


No matter what is in your compost, it is always a good idea to wear a dust mask when opening bags of soil amendments, and when spreading them in the garden. A mask will help protect you from breathing in airborne fungal spores.

Bat guano is used as a fertilizer, and provides supplemental nitrogen, according to this information from Oregon State University. It contains about 12 percent nitrogen. The ratio of N-P-K (nitrogen-phosphorus-potassium) is approximately 12-4-2.

A recent news story on National Public Radio highlighted the human health risks of exposure to bat waste (guano) in caves in Borneo. Both world travelers visiting bat caves and local harvesters of guano may be at risk of contracting very serious viruses, unless they take precautions (masks, gloves, and scrupulous hygiene). In parts of the United States (particularly the Ohio and Mississippi River valleys), there is a fungus called Histoplasma that is found in soil which contains bat or bird droppings. Gardeners who wear masks when digging in affected areas can avoid contracting histoplasmosis.

Bat and bird guano are allowed as soil amendments "with restrictions" imposed by the U.S. Department of Agriculture. They must be decomposed and dried according to the USDA Organic Regulations requirements for raw manure. I recommend contacting the manufacturer of the products and asking them about where they obtain their bat guano, and whether they meet NOP (National Organic Program) and OMRI (Organic Materials Review Institute) standards. You can also ask about their veterinary and phytosanitary certificates for these products, and whether they make certain the guano is harvested sustainably and without harm to the bats and their ecosystem or to the health of harvesters (particularly in countries without strong worker protection laws).


The Carex buchananii in my parking strip garden is now large enough that it's reaching out over the sidewalk and getting underfoot. Can I safely cut it back? Can it be cut to the ground in spring and allowed to start over?


Sedges like yours should not be cut back too far. The magazine Horticulture says you can "gather up the leaves in one hand and, using a pair of scissors, cut off the top third, including the long flowering stems. This will leave the plant arching out gracefully, but not trailing along the ground. It may be necessary to do this twice a year: at the beginning and end of the summer."

Val Easton, writing in the Seattle Times (October 8, 2008) says "sedges resent being cut back too hard, so if the foliage lasts through the year untattered, just leave it alone. If the older foliage looks messy, or the tips have been burned by winter cold, trim the sedge back modestly, by no more than a third at most, in March or April." Another thing you could do is to dig up and divide your Carex in March, and move it away from the edge of the planting bed.


A friend gave me a small bag of camphor wood chips. I have them in my car and like the smell. Someone told me that camphor can be toxic. Is is toxic to breathe, to burn, to human, to plants? Is it safe to just keep in my car and breathe?


Cinnamomum camphora (source of camphor wood) is in the Laurel family. According to Toxic Plants of North America (Burrows & Tyrl, 2013), "few toxicologic problems have been associated with the genus. However, when a camphor tree was planted in an aviary, 49 budgerigars died within 24 hours, apparently from its noxious fumes." As implied by its common name [camphor tree], all parts of the tree contain camphor. The intensity is greater in the leaves than in the wood. The tree's toxic properties have been known since the late 1800s, and most exposures are non-fatal and involve accidental ingestion of liniments that contain the oil from the plant. When inhaled, camphor is usually a mild irritant (perhaps not so mild at all if you are a bird!) and nervous system stimulant. It also contains low levels of toxic alkaloids.

If you wish to err on the side of caution, I would suggest not breathing the fumes, burning the wood, or using it in the garden (unless you are trying to suppress weeds, though the tree itself is considered a weedy species in some parts of the world, such as Australia). As you probably know, people have used camphor-based preparations in herbal and traditional medicine.

About medicinal uses and associated risks
About the tree
About the wood

The article "Camphor—A Fumigant during the Black Death and a Coveted Fragrant Wood in Ancient Egypt and Babylon—A Review," by Weiyang Chen, Ilze Vermaak and Alvaro Viljoen, offers a historical perspective, and does mention that the tree may have some phytotoxic/allelopathic properties as well (toxic to other plants).
"The fragrant camphor tree (Cinnamomum camphora) and its products, such as camphor oil, have been coveted since ancient times. Having a rich history of traditional use, it was particularly used as a fumigant during the era of the Black Death and considered as a valuable ingredient in both perfume and embalming fluid. Camphor has been widely used as a fragrance in cosmetics, as a food flavourant, as a common ingredient in household cleaners, as well as in topically applied analgesics and rubefacients for the treatment of minor muscle aches and pains. Camphor, traditionally obtained through the distillation of the wood of the camphor tree, is a major essential oil component of many aromatic plant species, as it is biosynthetically synthesised; it can also be chemically synthesised using mainly turpentine as a starting material. Camphor exhibits a number of biological properties such as insecticidal, antimicrobial, antiviral, anticoccidial, anti-nociceptive, anticancer and antitussive activities, in addition to its use as a skin penetration enhancer. However, camphor is a very toxic substance and numerous cases of camphor poisoning have been documented. This review briefly summarises the uses and synthesis of camphor and discusses the biological properties and toxicity of this valuable molecule."