Evie asks: My rhododendron leaves are withering and the whole shrub looks very stressed. This plant was given to me in the spring and appeared to be in good health. But now it is gradually decreasing. What should I do?
Looks like your rhododendron has a parasitic fungus called Phytophthora, or root rot. The fungus attacks the essential water-conducting tissue, which ultimately kills the plant. The problem can arise after hot, humid weather and in poorly drained soil.
Your rhodium may have had an invisible fungus problem when you had it. Dig up the plant and see if the base is brownish. The plant should have an abundance of white nourishing roots. The infected roots become blackened and stunted and eventually die. Do not replant in the same place.
One way to avoid the problem is to check the roots of a plant before purchasing it. If you see a plant that has stressed leaves, ask a vendor for permission to examine the roots by tipping the root ball out of the container.
Some species are resistant to root rot but can be difficult to find in the nursery. However, many nurseries are ready to place special orders.
One rhododendron that I know is more resistant to Phytophthora is “Caroline”.
In well-drained soil, plants have more resistance. When planting, add compost and plant shallow, on a mound. Cover the roots with soil as sunburn or exposed roots can make a rhododendron vulnerable to Phytophthora.
Howard asks: I have always appreciated the beauty of native plants in the landscape. Now, having lost our house and our garden to the fires, we start over with a new landscape. But we are concerned about the flammability of some native plants after the loss of our garden.
What would some of your favorite choices be if you were in our situation?
There are beautiful natives that are not necessarily a fire hazard. I am not a purist and I combine non-native plants with the same cultural demands as native plants such as low water consuming plants. It is very important to combine plants that enhance their location / area, such as coastal seascapes, warmer inland landscapes, woodlands, and shade exposures. The goal is to provide foliage texture in planting combinations, plant height variations and seasonal flowering.
Here are a few of my favorites: Penstemon heterophyllus planted en masse; delicious; Dudleya cymosa, planted in multiple and interesting galleries; annual wildflowers that reseed like California poppies; taller shrubs such as the native Garrya; silk pompom; trees such as Arbutus unedo “Marina”, common buckthorn and Rhamnus alaternus, a large shrub or small tree with dark evergreen leaves.
Other favorites include Feija sellowiana, a medium-sized evergreen shrub that has a spring bloom and attracts wildlife; colorful native yarrow; Achillea; millefeuille; Continuous flowering native beach aster Erigeron glaucus; wall flowers of several colors that attract butterflies and Mimulus or monkey flower, planted near bodies of water with a bonus of attracting butterflies.
Salvia sonomensis, or creeping sage, is a native plant of choice for slopes. Mass-planted Douglas-fir iris is good for spring color. And the Pacific dogwood or Cornus nuttalii works for a woodland garden.
âDesigning California Native Gardens: The Plant Community Approach to Artful, Ecological Gardens,â by Glenn Keator of Sebastopol and Alrie Middlebrook, is a great resource for those interested in designing with natives.
Tip for scorched slopes: As a temporary measure to reduce erosion, seed the scorched area with a fast-growing annual ryegrass. Winter rains will promote seed germination.
Matt asks: We have an evergreen Pittosporum shrub that has been in the same location for two years. My wife would like to move it. The shrub is healthy and we would hate to lose it. Is it safe to move around? If so, how should we proceed?
Here’s a technique nurseries and landscapers use to move trees and shrubs:
In January or February, use a long-edged, pointed spade and dig around the perimeter of the shrub about 2 feet from the main trunk. The roots must be cut. New roots will form inside the sectioned circle.
In the fall, prepare a new hole where you want to plant the shrub, making it wider but the same depth as the original hole. Go back to the plant, cut a new circle outside of where you previously pruned the roots, and carefully remove the shrub, keeping the root ball intact.
Plant like any new shrub and water it thoroughly, making sure there are no air pockets near the roots.
Dana Lozano and Gwen Kilchherr are gardening consultants. Send your gardening questions to The Garden Doctors at [email protected] The Garden Doctors can only answer questions through their column, which appears twice a month in the newspaper and online at pressdemocrat.com.