I planted 32 emerald-green arborvitaes between the end of August and early September. Plants range in height from 7 feet to 10 feet. They are turning brown quickly from the bottom up, with some browning throughout. I hit a layer of clay when I dig 12 inches. I mixed peat moss and pine bark mulch, and raised the trees 6 inches above the rest of the yard. I have been watering once a week and the soil stays moist. Am I watering too much? Plants get more shade than sun, but all trees get a few hours of sun. I don't know what to do and how to solve the problem.
-- James C., South River
There are several possible causes to the downfall of your arborvitaes. I believe soil conditions and lack of sunlight are leading to the problems with these trees. Arborvitaes grow best in full sun, and you have described your landscape as mostly shade with only a few hours of sun.
Shading and overcrowding of arborvitaes near other plants can prevent proper growth. I know from experience that even partial shading of arborvitaes from ornamental grasses caused browning in my yard. Once I moved the grasses, the arborvitaes recovered as they received the sunlight they needed.
You have described your soil as "clay" once you dig down 12 inches. South River can have heavy soils, with severe drainage problems. Although you did mix compost into the topsoil, I am concerned about the addition of pine bark mulch. This mulch should be used as a surface mulch only, not in the soil itself.
I am not sure of the amount of each that you have added to the mix, but if you've added too much bark mulch into the soil, you may have created soil conditions that rob plants of nitrogen as soil organisms break down large pieces of organic material in the soil.
In addition, you indicated that the plants were placed 6 inches above the surrounding landscape. If you plan to place a group of arborvitaes above the surrounding landscape, then you need to bring real soil up to the outward flare of the top of the roots. Covering roots with mulch or with soils that are high in pine bark could lead to desiccation and death of roots.
If you have a row of arborvitaes, it may be best to create a raised bed at least 1 foot above the surrounding area, and three feet to four feet wide. I created a similar bed in my yard, with a row of 14 arborvitaes that are all thriving. However, the plants in my yard are receiving full sun.
I have two large hydrangea shrubs that are healthy but did not produce flowers this year. What is the problem and how I can get these plants to flower next year?
-- Marie L., Freehold
There are many species of hydrangea available worldwide, but the most popular species in the United States is Hydrangea macrophylla, commonly known as bigleaf hydrangea. Most hydrangeas have beautiful, large and showy flowers that make a statement in almost any landscape setting.
Hydrangeas will grow best in a moist, well-drained soil and benefit from some shade, especially in warmer climates. Bigleaf, oakleaf (Hydrangea quercifolia) and smooth (Hydrangea arborescens) hydrangeas perform well on the edges of woods or on the north side of a house. Panicle hydrangea (Hydrangea paniculata) tolerates more sun than other species.
There may be situations where you will have healthy vegetative growth and very little or no flowering on your hydrangea plant. There are a few reasons why this happens. Shade and improper pruning can apply to all hydrangeas, but weather-related damage to flower buds is more restricted to the bigleaf hydrangea.
Most hydrangeas benefit from some shade, but too much will reduce flowering. As mentioned, this is a major factor for the panicle hydrangea ,which prefers full sun. Sunlight may change over time as nearby trees and shrubs grow and provide additional shade to the site. Over time, plants may have to be moved to provide adequate sunlight.
Improper pruning can influence the amount of flower development, too. Bigleaf and oakleaf hydrangeas flower on the previous year's growth, so if the plants are pruned in the fall, winter or spring, buds would be removed. Panicle and smooth hydrangea flower on current year's growth, so pruning in early summer would reduce or eliminate flower development in the same year.
The most common reason for little or no flowering in hydrangeas, primarily bigleaf hydrangea, is weather. Early fall freeze before the plant is completely dormant, extremely low winter temperatures or late spring freezes can damage the flower buds. The most common weather-related problem is the late spring freeze, which has been an issue over the past few years.
Branches may even die from these temperature changes. The plant will produce new buds from the base of the stem, but the stems will not likely produce flower buds later in the season.
Hydrangeas are wonderful plants as specimens or in a landscape border. Remember that it is important to provide the proper growing conditions for each species and protect them if possible to maximize flower production each year.
To learn more: Visit njaes.rutgers.edu or ifplantscouldtalk.rutgers.edu for gardening information and fact sheets. You can go to njaes.rutgers.edu/county/ for a listing of your local County Cooperative Extension garden help-line contacts throughout the state.
Bill Hlubik is a professor and agricultural and resource management agent for Rutgers Cooperative Extension-The New Jersey Agricultural Experiment Station, Rutgers University. He is also a host of the "If Plants Could Talk" television series on NJN Public Television.
Send your garden inquiries to Plant Talk, The Star-Ledger, 1 Star Ledger Plaza, Newark, N.J. 07102-1200 or firstname.lastname@example.org.