Growing Calendar for Perennials
Note: The Ohio State University Pocket Gardener will link you to good
information on a limited number of plants. The entire database can be downloaded (4.3 mb).
See Garden Links.
January through April
See Garden Tips Archives for those months.
May
> Dahlias can be set in the ground after the frost-free date. Ours are in pots on a screened porch, so they can get a jump start on the season. (See March Archive) Ours need to be pruned as soon as they begin to grow, then staked or caged, or they'll become top heavy and collapse.
> A dose of fertilizer right before rhododendrons, azaleas, and roses bloom will produce stellar blooms. After they bloom, clip the dead blooms, but be careful, because the new leaf growth are right below the dead buds. Their lower branches can be propagated by layering.
> If you have a ladder and the time, (HA!) prune lilacs and forsythia after blooming. Pruning later in the summer may result in flower bud loss for the following year.
> Plant hollyhocks, foxglove, and delphinium. Russian sage, globe thistle, and 'Foxy' foxglove should be planted in front of 'Pacific Giant' delphiniums. 'Sensation' cosmos also look nice with hollyhocks; when the latter are fading, the former are often peaking.
> Plant a rudbekia in front of a daylily and a 'Torch Light' gaillardia behind it. When the daylily dies back, the gaillardia will flop over the daylilly, and the rudbekia will also hide the faded leaves. This triage will provide color throughout the growing season and, since they tolerate poor soils, can be naturalized in a meadow. The annual dwarf cosmos, 'Brite Lights,' also looks good with these perennials.
June
According to the local nursery where I purchased Hydrangea macrophylla, 'All Summer Beauty', this cultivar is a hardier hydrangea. I learned later this variety blooms on old growth and should not be pruned, which may account for lack of blooms the past 3 years. If we get no bloom next year, I might consider moving it to a sunnier spot. Winter injury and lack of sufficient sunlight are listed as the most common reason for lack of flowering. A neighbor has a healthy looking one growing on their east wall, so I know they will bloom here. This shrub is worth the effort if it blooms.
Black Cohosh (Cimicifuga racemosa; Bugbane) takes several years to germinate outdoors, so we broke down and bought one to plant in our shade garden. We will try seeding in some clay pots this fall and bury them in the same garden where they will receive adequate moisture. The roots are used as an expectorant and to control tinnitus (ringing in the ears).
Our Astilbe, purchased last year at a garden club sale for our shade gardens, are flourishing under pine trees.
July
Perennials prefer to be transplanted in the fall, so this month is the best time for seeding them indoors. See March Archive in Garden Tips.
In early to mid summer, thyme forms small tubular flowers that are very attractive to bees. Harvest some before they flower for drying. Wooly Thyme grows between cracks in cement or bricks. The beauty of these types of thyme is that they tolerate a fair amount of traffic and they release a fragrance at the same time.
August
Bee balm, gaillardia, rudbekia, globe thistle, Shasta Daisies, Lambs' Ears are in peak bloom. Tiger lilies should also be peaking now.
The best time to cut flowers (and herbs) is in the morning before the dew dries. They should be 'cured' in water in a dark place for about 8 hours before arranging.
One of this gardener's favorite lilies is the very fragrant 'Casa Blanca' Oriental lily. This bulb is worth the labor of surrounding it with hardware cloth during planting. In a meadow are like ours, pine voles, ("meadow mice") will make short order of bulbs.
Prepare beds for a September planting of spring-flowering bulbs, ornamental grasses and shrubs, perennials, including chrysanthemums. (Regions south of Zone 4-5 should wait till October to plant.)
September
Cultivating
The spikey centers of perennials echinacea, gaillardia, and globe thistle offer enough for sharing as the photo below demonstrates. Bees and butterflies seem to prefer them to other members of the daisy family, e.g., rudbekia or Shasta daisies.
 Globe Thistle |
 Echinacea |
* Watering may still be necessary if temperatures are warm enough.
* Annuals in container gardens are a bonus in the fall, when you can move pots around to track the sun.
Geraniums, petunias, and basil next to our south-facing cement porch remain impervious to low nighttime temperatures because the porch stores heat during the day.
* Calendula, sulking during the summer heat, now enjoys a comeback when temperatures cool down.
* To harvest sunflower seeds, wait until the seeds are fully grown and firm, then cut the head leaving one foot of stem. Hang heads in a dry, airy spot to finish ripening. Do not store sunflowers one on top of another or they may rot. (Va Tech Extension)
'Valentine' 
'Autumn Harvest'
Pruning and Dividing
* Perennials should be pruned systematically after blooms have peaked, leaving some leaves for plants to continue producing food for a healthy root system.
* Give them a rest before dividing. This is a committment to finding a suitable new planting site. Something to keep in mind when purchasing them! One plant can go a long way, if given the right growing conditions.
October
Source of Table: Clemson University, Home and Garden Center, Prepared by Karen Russ, HGIC Information Specialist, and Bob Polomski, Extension Consumer Horticulturist, Clemson University
Perennials for ShadeThose marked with a * will tolerate the most shade.
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Perennials for Hot, Dry Conditions
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Tolerant of Moist or Damp SoilsThose marked with a * will tolerate wetter soils.
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Perennials for Poor, Sandy Soil
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Attractive FoliageThose marked with a * are gray or silvers that tolerate heat and humidity.
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Perennials That Can Be Invasive
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