The Perennial Q & A section provides answers to common questions about perennials and their care. We encourage you to look in other areas of this website and at individual plant records in the Perennial Encyclopedia if you do not find the answer you are looking for here.
Perennials have enjoyed a huge surge of interest by today's gardeners in recent years. Money-wise people know that you only have to buy a perennial once, not every year like annuals. Water-wise folks know that many perennials require much less water than annuals which need to be watered daily.
It's difficult to choose just a few of the most popular perennials since there are so many great ones, but here goes...
You may want to try using our search tool for Stellar Sellers and Award Winning Perennials for more ideas.
A number of perennials make excellent container plants. Perennials that have colorful and unique foliage are the best. Here are some suggestions:
For hot, dry sites such as decks, sunny porches, etc...
For partial to full shade...
Though daylilies are generally very low maintenance and are not bothered much by pests or diseases, occasional problems may occur. Under certain conditions, thrips and mites may feed on daylilies. Many people simply tolerate the occasional damage these insects do to daylily foliage and blossoms. Others choose to apply pesticides appropriately chosen. Orthene is effective in controlling thrips. Mites usually infest daylilies that are drought-stressed. Keeping your daylilies well-watered will usually keep mites at bay. Avoid using Kelthane, a common miticide on daylilies, as serious foliage damage to the daylilies will occur. Daylilies also are occasionally infested with foliage diseases. Two of the most common are leaf streak and bacterial leaf spot. Commonly available fungicides such as Dithane or Daconil are useful in controlling such diseases. None of these problems is so damaging to daylilies that special care is necessary. In most cases, even if you do nothing, your daylilies will perform satisfactorily.
The following awards are given by the American Hemerocallis Society (AHS) annually:
A daylily is a perennial which is characterized by its long, narrow, strappy leaves and its flowers which each last only one day (hence the common name Daylily).
Its botanical name is Hemerocallis. Daylily is one word, not two, although even The New York Times regularly gets this wrong. These outstanding plants are now the best selling, most popular perennial in most of the United States.
Daylilies have a crown which is the intersection where the roots and foliage meet. The foliage emerges from the center of this crown in fans. A three year daylily clump may contain 10-30 individual fans, most of which will produce a bloom scape.
When the foliage matures in midsummer, the flower stalk emerges from the center of the fan. Each scape contains 10 to 40 or more buds, thus making a progression of bloom which may extend over three to four weeks. Some daylilies are repeat bloomers and others can flower all summer long, but these are exceptions.
Daylilies have a specialized root system. They are not bulbs, tubers, or corms. Instead, they have fibrous, fleshy roots of all different sizes. The larger ones may be as thick as your finger! These roots store the nutrients and water which serve as the plants' energy reserves.
Most of the work in daylily hybridizing (coming up with new cultivars) has been performed in the United States. Major advances in improving daylily quality and diversity have been made in the past 50 years.
Daylily hybridizers and specialists typically classify daylily foliage in three categories:
Dormant means deciduous. Dormant daylilies lose their foliage completely when frost arrives in the fall. They then remain leafless or without foliage for some period of time that is variable both by cultivar and growing region. Dormancy may be affected by day length and temperature change.
Evergreen actually means ever-growing or foliage-persistent. Evergreen daylilies continue growth year-round in mild climates that do not experience below-freezing weather in winter. Evergreen daylilies attempt to grow continuously in colder, northern climates, but their growth is interrupted by cold temperatures. In very cold climates, evergreen daylilies essentially halt their growth during the winter. In transitional climate zones, where the soil does not remain continuously frozen through the winter, evergreen daylilies may continue to push up new foliage on warmer days.
By definition, a semi-evergreen daylily behaves like a dormant in the north but acts like an evergreen in mild, frost-free climates. Semi-evergreens theoretically perform reasonably well in both southern and northern gardens. Semi-evergreen daylilies possess foliage that is slower to die back in the fall than the dormants. Semi-evergreens are often quicker to re-emerge in the spring than dormant types.
In northern regions...
Much like it is easier for humans to get a sunburn in the hot afternoon sun than in the morning, the same holds true for plants. Morning sun is much weaker in intensity than afternoon sun. Even though part shade is technically defined as 4-6 hours of direct sunlight, there is a huge difference between 4-6 hours of afternoon sun vs. 4-6 hours of morning sun.
As a general rule, plants that prefer full shade to part shade need to be planted where they will have exposure only to morning sun or where they will receive no direct sunlight at all.
Conversely, plants that prefer full sun need to be planted where they will receive an absolute minimum of 6 hours of direct afternoon sun, preferably much more.
When plants are sited in improper lighting conditions, they will tell you if you look closely. Some will stretch their stems and lean awkwardly towards the direction the sun is coming from. Others will not grow nearly as large as you would expect them to. Many will reduce their flower production or will not flower at all if there is not enough sunlight to produce buds. Some will just give up and die completely. Listen to your plants--they will tell you what they need!
A hybridizer is a person who works on breeding new plants. They use many methods, one of which is hand pollination. Many hybridizers dedicate their lives to this work and may work on one kind of plant for 20 or more years in order to find the best new cultivars.
Fibrous Root - Composed of profusely branched roots with many lateral rootlets, often with no main or taproot development. Many perennials with fibrous root systems are dividable. Example: Achillea.
Taproot - The main descending root of a plant. Generally, perennials with tap roots prefer cool temperatures and dry soil conditions once they are planted in containers. If temperatures are too warm, they put their energy into top growth without establishing a satisfactory root system. Lupines, in particular, benefit from being grown in temperatures around 40 degrees F for about six weeks.
Rhizome - A specialized slender or swollen stem with branching close to the soil surface. It produces roots, stems, leaves and flowers along its length and at its apex. Examples of plants with rhizome-type roots include Acorus and Bearded Iris.
Corm - An underground, bulb-like portion of the stem of a plant consisting of fleshy tissues. Example: Crocosmia.
Here's a basic example which illustrates the significance of the latin words in plant names:
Dicentra spectablis 'Alba'
The first word is always the genus name. In this example, Dicentra is the genus. It is always capitalized and is never written in italics. A genus is a group of plants that all share some common characteristics. It can include from one to a thousand or more species. The common names for many plants, such as Hosta, are also their latin names.
The second word is always the species name. In this example, spectablis is the species. It is always written in italics and is never capitalized. Members of the same species share even more common characteristics than those in the more general genus. Sometimes a species is further separated into subspecies.
The word(s) listed in single quotation marks is the cultivar name. In this example, 'Alba' is the cultivar name. It differs from the straight species, Dicentra spectablis by its flower color. The cultivar name often holds clues to the plant's characteristics, such as 'Alba' which means white, referring to its flower color.
The USDA broadly approximates similar US growing regions and gives them a numerical classification. The zone information provided on this website is a guideline to the hardiness of individual perennials within those zones. Within any region there are variable conditions such as snow cover, moisture levels, microclimates, and many other factors which can alter the zone hardiness. We use the 1990 USDA Zone map in addition to personal experience as a basis for the information included in this website and all of our publications.
Zones listed in parenthesis ( ) on this website represent marginal hardiness with protection. For example, a plant that is listed as zone (4)5-9 would be marginally hardy with protection in zone 4, but should be reliably hardy in zone 5.
The following perennials need to be grown dry:
Numerous perennials can be divided and replanted with great success. Root systems like those of Ajuga can be divided by hand, whereas others may require a sharp knife.
Some bare root perennials that typically can be divided include:
Cool Season Grasses
Cool season grasses are at their prime during the cooler months of fall, winter, and spring, and usually bloom before the warmer summer weather arrives. Many are evergreen. Cool season grasses should be planted in the fall or spring as they will put on the most growth during these months. Cool season grasses include: Calamagrostis acutiflora, Festuca, and Helictotrichon.
Warm Season Grasses
Warm season grasses grow most actively during the warmers months, then flower in late summer or fall. Most go completely dormant in winter. Warm seasons grasses are not recommended for fall planting. It is best to plant them from early spring through late summer. Warm season grasses include: Acorus, Arundo, Andropogon, Calamagrostis brachytricha, Carex, Chasmanthium, Cortaderia, Erianthus, Hakonechloa, Miscanthus, Panicum, Pennisetum, Schizachyrium, Spodiopogon, and Sporobolus.
SedgesSedges, or Carex, are not true grasses at all, though they certainly look similar. They are actually members of the Cyperaceae family, which includes about 4,000 species worldwide. We offer several varieties of Carex, including variegated and yellow varieties, and ground cover and clumping types. Sedges tend to grow more like warm season grasses, so we recommend receiving them from early spring through late summer rather than in the fall.