Editor’s note: This week we have a guest article by Dr. Tony Keinath, a researcher and avid gardener. Amy Dabbs will return in two weeks.
By Anthony Keinath
Special to The Post and Courier
Is it my imagination, or do most flowering plants prefer morning sun, afternoon shade? Many plants I would like to grow seem to need this pattern of sunlight. Gardenia and Japanese maple are just two examples that come to mind quickly.
Most areas of my yard get morning shade, afternoon sun. This is due to the placement of the two-story house with attached garage on a narrow suburban lot and five old trees on the eastern and southern exposures. Planting beds on the north and west sides of the building are deeply shaded in the morning, and then abruptly change to blazing afternoon sunshine.
In the back yard, sunny and shady areas shift continuously during the day with the movement of the sun. Through trial (and error) over the past 10 years, I have learned which plants will thrive where mornings are shaded and afternoons end in full sun. Here is how to have a respectable showing of blooms in these areas year round.
Choose plants that prefer “sun to part shade.” The astilbe withered. The Jacob’s ladder collapsed overnight. The columbines cooked. With the summer sun appearing about 1 p.m. and lasting until 8 p.m. on clear days, plants that require “part shade to shade” get too much sun and heat in the afternoon.
However, plants that tolerate “sun to part sun” usually get enough sun to bloom just fine.
Careful plant selection, with an emphasis on sunlight preferences, is the key to success. Some flowers, such as ‘Goldstrum’ black-eyed-Susan or snapdragon, will flower later when grown in part sun rather than in full sun, but they are glorious nevertheless when they do.
Use microenvironments. Check your gardening space at different times of the day and see in which spots the sun appears first. Plant snapdragon and marigold where they will get the most sun, and plant hybrid Lenten rose, holly fern, or Southern shield fern where shade lingers. Southern shield fern grows at least 21/2 feet tall and can take some sun; it is perfect for the back of a part-shade border against a building that blocks the sun. I have a ‘Victory’ pyracanthus (firethorn) espaliered on a west-facing wall to take advantage of the sun appearing over the steep garage roof before it reaches the lower portion of the bed.
Give them everything else they need. Because some of these plants may not get as much sun as they prefer, pamper them in other ways. Amend the soil before planting and make sure the soil pH is optimum. Does the plant prefer wet, moist, medium, or dry soil? Add sand or compost to the potting hole to improve drainage, but use peat moss to keep soil moist. Make a “mini” raised bed for plants that prefer well-drained soil.
Be sure to adjust watering according to the amount of rain and the amount of water in the soil. Part-sun areas dry more slowly after a rain than full-sun areas, but after several afternoons of hot sun, it will likely be time to resume watering.
Watch out for pests. Some plants may be more susceptible to insects or diseases if they must make do with less sunlight than is optimal. For example, crepe myrtle planted in part shade is more prone to aphid problems than crepe myrtle planted in full sun. Watch for scale insects on the backsides of shrubs against a building. Sooty mold can be a problem on gardenia planted in part shade. Remember also to be extra careful not to wet leaves when watering plants in part shade, because drying times are longer than in sun.
What plants need
Part sun unless noted:
‘Carissa’ or dwarf Burford holly
Variegated false holly (part shade)
Japanese yew (part shade)
Annuals (part sun unless noted):
Hybrid zinnia (Pinwheel or Profusion series)
Wax begonia (part shade)
Ageratum (part shade)
Bergenia (grow as annual)
Foxglove (grow as annual)
‘Mystic Spires’ salvia
Southern shield fern
Anthony Keinath is professor of plant pathology at the Clemson Coastal Research and Education Center, a Master Gardener instructor and an avid gardener. Contact him at email@example.com.