Extension Consumer Horticulturist, Clemson University
How do I get rid of what my neighbor calls wild carrots? They are taking over my yard and flower beds and I don’t know what to do to stop them.
—C.E., Bidwell, OH
Answer: This biennial weed is indeed a wild carrot (Daucus carota). Also called Queen Anne’s lace or devil’s plague, it hails from Asia and Europe, but has become naturalized in this country. In the spring seedlings emerge and produce a basal rosette of foliage. In the second year plants produce a one- to three-foot flower stalk. All parts of this plant emit a carrotlike odor when crushed.
The inflorescences are umbels composed of numerous individual white flowers. The center flower is often red or purple. When the flowers fade and turn brown, they curl upward and meet to form a nestlike structure. Inside are bristly barbed seeds that are shed as the plant dies. Each plant is capable of producing up to 4,000 seeds before it dies. Most seeds germinate within two years of dispersal, but they may persist in the soil for up to seven years.
Prevent infestation by pulling young plants when the soil is moist and you can remove the entire taproot. Hoe out or till under plants before or during bloom. Maintain a two- to three-inch-deep mulch in your beds in the fall to suppress germination. Regular mowing and proper lawn maintenance will curb lawn infestations. A pre-emergence herbicide containing isoxaben (Gallery) can be applied in the fall. A postemergence herbicide containing 2,4-D, dicamba, and MCPP (Trimec) can be used to spot treat individual weeds in the lawn. Glyphosate (Roundup) can be used in flower borders and beds.
I found some old fertilizer in a bag. It has turned into concretelike lumps. Can I still use it? —Y.T., by e-mail
Answer: Yes—all of the nutrients are still contained in the lumps, which will need to be crushed with a hammer before they can be applied. This caking of fertilizer is owed in part to the nature of the material and to poor storage. Synthetic fertilizers, both granular and powdered, are prone to caking.
Some fertilizers are more hygroscopic, or apt to absorb moisture, than others. For example, fertilizers containing calcium nitrate or ammonium nitrate are more hygroscopic than urea, ammonium sulfate, potassium chloride, calcium phosphate, potassium sulfate, or calcium sulfate. To help prevent caking, some manufacturers apply a coating to granular ammonium nitrate and ammonium nitrate-based fertilizers.
To reduce the likelihood of this happening again, store fertilizer in its original bag in a protected dry location. Alternatively, place the bags in five-gallon buckets with tight-fitting lids. Never leave unused fertilizer in spreaders, because it will rapidly corrode any metal parts, quickly ruining the equipment.
Finally, purchase only the amount that you intend to use in the near future to reduce the amount you have to store.
I collected seeds from my bearded irises, and now I’d like to know how to plant them.—CD., Muncie, IN
Answer: Irises are usually propagated by dividing the rhizomes six to eight weeks after bloom to reproduce the named cultivar. Growing them from seed is usually reserved for propagating species irises or for breeding new cultivars from predetermined crosses. Although the offspring from your seeds will not be true to type, the ease of sowing them and the possibility of finding a diamond in the rough makes the experiment worthwhile.
The seed should have been collected when the green capsules turned brown and dry and began to split open. Store the seed in a paper cup or other open container in a cool, dry place. In the fall, direct sow the seed outdoors in a well-drained location. Alternatively, you can sow them in a flat filled with store-bought seed-starting mix. Sink the flat into the ground so the top is level with the surrounding soil. The seeds should be planted one-half to three-quarters of an inch deep and about an inch apart. Keep your nursery bed moist over the winter. Leaching winter rains remove germination inhibitors from the seed coat, and the cold provides the cool, moist stratification required by the seeds.
Expect germination to be erratic. Some seedlings will appear the following spring and others will emerge a year after. When they have reached a height of three or four inches, transplant them to a permanent location in your garden. Your bearded iris seedlings can be expected to bloom in their second year after germination.
During a recent visit to a public garden, I saw an empress tree that had huge tropical-looking leaves. They must have been at least three feet in width. I was told that cutting it down to the ground resulted in these gargantuan leaves. How is that possible? —T.F., Vancouver, WA
Answer: The pruning technique is called coppicing, a practice that originated in Europe centuries ago as a firewood production system. The tree is repeatedly cut down to generate an abundance of small stems. At the time it was considered wasteful to cut down a full-grown tree and chop it up for firewood (indeed, it was a punishable offense—see “Ancient Groves” by Charles Elliott, November 1994). Billhooks and axes were used to coppice trees, cutting them cleanly to near soil level. In response, the tree produced clusters of vigorous, straight shoots that were then cut for firewood, building materials, tool handles, basketwork, and fencing.
Nowadays, coppicing is used for ornamental purposes: to accentuate the colorful stems and shoots of deciduous shrubs in winter, to create bold-looking foliage, and to maintain trees in confined spaces. A variation is pollarding, sometimes called high coppicing. The cuts are made higher up on the plant, either back to the main trunk or to the end of a scaffold branch. Such repeated cutting creates curious-looking, clublike growths topped by arrow-straight shoots.
The best candidates for coppicing are un-grafted shrubs and trees that produce flowers and fruit on the current season’s growth or possess colorful leaves or vibrant stems. They include butterfly bush (Buddleja davidii), beautyberry (Callicarpa spp.), blue mist shrub (Caryopteris clandonensis), Tatarian dogwood (Cornus alba ‘Sibirica’ or ‘Elegantissima’), red osier dogwood (C. sericea
‘Bud’s Yellow,’ ‘Cardinal’, ‘Silver and Gold’), pee gee hydrangea (Hydrangea paniculata ‘Grandiflora’), and filbert (Corylus avellana).
Trees for coppicing include striped maple (Acer pensylvanicum ‘Erythrocladum’), with its young red stems, hornbeam (Carpinus betulus), red-twigged linden (Tilia platyphyllos ‘Rubra’), contorted mulberry (Morus bombycis ‘Unryu’), pussy willow and other willows (Salix spp.), chaste tree (Vitex agnus-castus), and smoke bush (Cotinus spp.). In late winter or early spring, before bud break, cut the plants to one to three inches above the ground. Latent buds at ground level will yield new shoots, and these in turn can be cut back again each year or every few years. To encourage this swift regrowth, apply fertilizer to coppiced plants as new growth appears.
The especially large leaves that resulted from coppicing the empress tree (Paulownia tomentosa) you saw at the public garden are an example of juvenile leaves. Certain woody plants, including Paulownia and Catalpa bignonioides, have dramatically different juvenile foliage, in this case leaves that are 10 times larger than the leaves on mature trees.
I am intrigued by Virginia bluebells and other woodland perennials that appear in early spring for a short time before going dormant and disappearing. Can you tell me more about this curious life cycle?
—R.D., Bay View, MD
Answer: Virginia bluebells (Mertensia virginica) belong to a group of spring-blooming perennials called spring ephemerals, under-story plants that can be found in deciduous forests in North America and eastern Asia. Other spring ephemerals include cardamine, spring beauty (Claytonia spp.), Dutchman’s breeches (Dicentra cucullaria), Japanese bleeding heart (D. spectabilis), toothwort (Dentaria spp.), shooting star (Dodecatheon spp.), and trout lily (Erythronium spp.).
Spring ephemerals rapidly emerge from dormancy in response to rising soil temperatures and grow in the high light conditions that occur on the woodland floor of deciduous forests before the canopy leafs out. Their aboveground growth is compressed into 40 to 60 days, unlike other herbaceous perennials that continue to grow throughout the spring and summer. They have high photosynthetic rates despite cooler temperatures. They have high nutritional requirements, too, which is why they are found in rich forest soils. However, spring ephemerals also have a high resorption efficiency. They can recover a large fraction of nutrients previously used in their aboveground tissues when their leaves die back as the canopy above them leafs out. A large proportion of their photosynthetic resources are channeled into rhizomes, corms, or tubers, helping them survive unfavorable periods. H