Monday, July 29, 2013

August Calender of Triangle Gardening Programs

Orchid Growers Day, August 3,
at the JC Raulston Arboretum.
NC Botanical Gardens
Location: 100 Old Mason Farm Road, Chapel Hill, NC.

Home Landscape Design
Date: Saturday, August 3
Time: 9:30 a.m. - 12:30 p.m.
JoAnn Overton, Landscape Designer

This workshop addresses the typical challenges of homeowners in this area. Participants learn how to approach a landscape design project, how to implement a plan with sustainable materials and finally, you will be given a list of native plants of this area frequently used in home landscapes. Specific topics will include analyzing the property for wind and sun orientation, a functional flow, and treating special features of your landscape. The concepts of sight line, public and private areas and "rooms" will be discussed. Fee: $35 ($30 NCBG members)

Soil Ecology
Dates: Saturdays, Aug 3, 10, 17, 24
1:00 - 4:00 pm
Instructor: Nicolette Cagle, Ecologist

This course is intended for a broad audience. Students are introduced to the complex world of soils including information on how they are formed, characterized, and populated by a wide array of organisms. An overview of soil types is presented, followed by the study of typical Piedmont soils and their properties. The various roles that soils play in both human society and ecological systems are discussed. No prerequisites. Fee: $125 ($115 NCBG members)

Dates: Saturdays, Aug 10, 17, 24, 31
Time: 9:15 am - 1:15 pm
Instructor: Olivia
Lenahan, Horticultural Scientist

This course is introductory in nature and designed for a broad audience. It is a fundamental core course for students enrolled in either of the NCBG certificate programs. Basic principles of botany including taxonomy, anatomy, morphology and physiology are covered. Class time is divided between lectures and examining/dissecting samples. There are also opportunities for making observations in the gardens. No prerequisites.Fee: $150 ($135 NCBG members)

JC Raulston Arboretum
Location: Ruby C. McSwain Education Center, JC Raulston Arboretum at NC State University, 4415 Beryl Road, Raleigh, NC

Orchid Growers Day
Hosted by the Triangle Orchid Society in Cooperation with the JC Raulston Arboretum
Date:  August 3, 10–4 p.m. – (Check In opens at 9:30 a.m.)

Plantsmen's Tour: "Perennials for Shade"
Mark Weathington, Assistant Director and Curator of Collections
Date:  August 13, 9–10:30 a.m.

Friends of the Arboretum Lecture: “Outlook for Turkey's Agriculture"
Date: August 15, 7:30–9 p.m.
S. Metin Kara, Ph.D. Department of Field Crops, Ordu University, Ordu, Turkey
Turkey, with a wide range of climatic conditions and rich natural resources, has a high agricultural potential which enables the cultivation of several crop species. Agriculture still plays an important role in the economy of Turkey, but its share has declining gradually in the last years. With increased research and investments in agriculture, productivity and profitability are expected to increase in the years ahead so that the country can economically benefit from its natural resources.

Sarah P. Duke Gardens
420 Anderson St., Durham, NC 27708  Please call 919-668-1707 to register.

Walk on the Wild Side
Date:  August 1, 11:00 a.m.
Explore wild North Carolina in these walks through our Blomquist Garden of Native Plants. Join curator Stefan Bloodworth or horticulturist Annabel Renwick on the first Thursday of every month for discussions of seasonal interest. Please dress for the weather. $7; $5 for Gardens members and Duke students and staff. Registration required (parking fees apply). To register, or for more information, please call 919-668-1707.

Durham Garden Forum
Meetings are held at Sarah P. Duke Gardens on Tuesday Evenings from 6:30-8 p.m.
Membership is $25 for the year (which runs April – March) or each lecture is $10. No preregistration is required. Contact information is

(None listed for August 2013.)

NC Extension Gardener Seminars
Sundays. Complete program information at
Registration required, but free to the public.

Cool Season Vegetables
Date:  August 11, 3-4 p.m.
Location:  North Regional Library, Durham
Contact:  919.560.0231

Container Gardening Around the World
Date:  August 18, 3-4 p.m.
Location:  South Regional Library, Durham
Contact:  919.560.7409

Eggs Over Easy
Date:  August 25, 3-4 p.m.
Location:  East Regional Library, Durham
Contact:  919.560.0203

Thursday, July 18, 2013

Got herbs? Community gardens are great places to grow a communal herb plot for all to enjoy!
See the July newsletter of the NC AT&T Community Gardens: Herbs_Veggie of Month_July 2013_Durham
For instructions how to build an herb spiral see:

Evening in the Garden with Chocolate and Roses

Come enjoy some rich chocolates in Witherspoon Rose's anniversary garden while listening to a talk on "Enjoying your Rose Garden."

Witherspoon Rose Culture will host "Evening in the Garden with Chocolate and Roses" 6-8 p.m. Friday, August 9, 2013.

Address:  3312 Watkins Rd, Durham, North Carolina 27707

Wednesday, July 17, 2013

Pest Management Spotlight: Horticultural Oils

Capnodium sooty mold on a holly.
By J.S. Corser (FH)
Durham Co. Master Gardener
Oils are complex. They can be an extra virgin companion to focaccia breads, a fishy supplement in the fight against cardiovascular disease, or a devastating killer to marine wildlife with decade-long impact.

Or, the same oil can be a killer to voracious, piercing and sucking insects and sooty molds, while playing savior to the holly bush on which the two are attacking. Enter the role of horticultural oils.

Horticultural oil is considered a practice of Integrated Pest Management (IPM) for controlling insect damage to plants.  They consist of ingredients and a mechanism comparatively less harmful to the environment than commercial grade pesticides1. One of the main advantages of horticultural oils is that they dissipate through evaporation, and leave little residue on the plant, which in turn leaves little chemical impact to the plant’s soil and ecosystem. Plants (and pests) need to be thoroughly coated with the horticultural oil to be truly effective, however, once dried the oils will cease to have the desired insecticidal effect1.  Another advantage that is making oils a popular tool in IPM is that they are generally easy to apply with ready-to-use formulations, can be applied with existing spray equipment, and can be combined with other commercial pesticides to extend performance to a broader range of pests. More notably, unlike commercial pesticides, insects have developed no immune responses to horticultural oils4!

Horticultural Oils Potential Hazard to2:
Water quality (aquatic wildlife)
Natural enemies (beneficial)
Honey bees
People and other Mammals
Long Term
Not acutely toxic
Very Low
Not listed


Toxicity category2: III - Apply only during late evening, night, or early morning

 Horticultural oils were first used centuries ago to control mites and scales on fruiting trees3. They were first developed as a thick, winter or dormant-season oil treatments (before bud break) to kill eggs of caterpillars, mites and insects, such as scales and aphids, that spent the winter on the plant4. Today, gardeners and commercial growers alike can use horticultural oils on not only fruit trees, but shade trees and woody ornamental plants to kill scale, aphids, mites, and other soft-bodied insects1. In addition, lighter formulations horticultural oils have been recently developed for use throughout the growing season for flowers, vegetables and other herbaceous plants. These oil products are commercially labeled “summer,” “superior,” or “supreme oils”1.

The main difference between heavy dormant oils and lighter summer oils is that dormant oils have 50 to 90% unsulfonated residues4 (50 to 10% unsaturated hydrocarbons resulting from the plant’s chemical reaction with sulfuric acid in the oil), and they tend to damage green plants and tender stems. Summer oils have 92 to 96% unsulfonated residues (8 to 4% unsaturated hydrocarbons) and they are much safer to use on leaves and stems4.

How do horticultural oils work? First the pest must be thoroughly coated with the oil. The density of the oil treatments subsequently blocks the respiratory “spiracles” through which insects breathe, causing them to die from asphyxiation. Oils have also been clinically shown to negatively interact with insect body fatty acids, thus interfering with some insects’ metabolism3. Horticultural oils also clog the piercing and sucking stylets in the Homoptera insect order, thus blocking the transmission of some plant viruses by aphids3. Lastly, horticultural oils can help smother established populations of powdery mildew and sooty molds4 allowing the gardener to more easily hose off the infestation.

DIY and penny-savers might be tempted to create their own a horticultural oil, but getting the correct viscosity and insecticidal compounds is a bit more complicated than pouring some Wesson™ or extra virgin into a spray bottle with a gush of water and shaking it up. Commercial horticultural oils are synthetic, refined petroleum products, commonly also known as “mineral oils”. Impurities in the oil which are associated with plant injury, such as aromatic compounds and compounds containing sulfur, nitrogen or oxygen, are removed3. Filtration, distillation and de-waxing process complete the production of the finished base oil; from there the base oils is combined with an emulsifying agent that allows it to mix with water. This mixture usually is used at about a 2 percent dilution3. If organic and simple (not to mention less fussy and scientific) is more the philosophy of a residential gardener, then he can create a homemade horticultural oil with one gallon of water to four tablespoons of cottonseed oil2. Cottonseed oil is generally considered the best insecticidal of vegetable oils. Soybean oil is another choice which has been deemed fair-to-good control of some insects and mites1.  

The darling, however, of the organic horticultural oils market is neem extract from the neem tree, Azadirachta indica3. Different compounds found in neem seeds, specifically azadirachtin, have proven efficacy as insecticidal agents. Interestingly, neem oil (from the seed) does not contain azadirachtin nor terpenoid compounds found in other parts of the seed, but has shown doubly effective as both a fungicide and insecticide. Consumers can find several over-the-counter products sold in nurseries labeled “neem” containing the oils of neem seed for greenhouse-grown ornamentals1. They have shown good plant safety, but there are some precautions for use on impatiens, fuschia, hibiscus, some roses, ornamental olive and some carnation varieties3.


The following precautions are recommended whenever using a horticultural oil on a woody plant:
  • Avoid using oils on plants that tend to be oil-sensitive. Avoid drift onto sensitive plants.
  • Do not apply when temperatures are excessively high (above 100 degrees F) or low (below freezing). High temperature limitations are primarily related to the drought-stress status of the plant. Plants under stress may be damaged. Those not stressed are much less likely to be damaged by an oil application. Dry conditions without plant stress generally reduce risk of injury by oil, because evaporation is more rapid.
  • Do not apply oils during freezing weather. This can cause the emulsion to break down and produce uneven coverage.
  • Do not apply oils if plant tissues are wet or rain is likely. These conditions inhibit oil evaporation. High humidity (above 90 percent) also may contribute to injury risk, while low humidity generally reduces it.
  • Do not spray when shoots are growing.
  • Avoid treating plants during the fall until after winter hardening has occurred. Fall treatments have sometimes caused increased susceptibility to winter injury.
  • Do not apply oils in combination with sulfur or sulfur-containing pesticides such as Captan or Karathane. They can react with oils to form phytotoxic compounds. Because elemental sulfur can persist for long periods, label directions on most oils prohibit their use within 30 days of a sulfur application.
  • Some species are more sensitive to oils including: black walnut, Cryptomeria, Douglas fir, hickories, junipers, cedars, Japanese and red maples, redbud, smoke tree, Alberta spruce


1.  Galloway, W.E. (2011). Rodale, Inc. “Horticultural Oils Explained: What are horticultural oils and where can I get them?”. Retrieved from,

2. Statewide IPM Program, Agriculture and Natural Resources, University of California.
(2012). UC IPM Online. The Regents of the University of California. Retrieved from,

3.  Cranshaw, W.S. & Baxendale, B. (2013). Insect Control: Horticultural Oils, Fact Sheet no. 5.569. Colorado State University Extension. Retrieved from,

4.  Baker, J.R.  (2011). “Horticultural Oils as Insecticides.” ENT/ort-45.  North Carolina State University Extension. Retrieved from,

5.  Products List Search: horticultural, oils. (2011). Organics Material Review Institute. Retrieved from,

Thursday, July 11, 2013

Must-Have Books for a Gardening Library

Looking to trim your gardening library with only a few essential books? Then start with this bibliography compiled from suggestions of Durham County Master Gardener volunteers. You'll have great references and no fillers!
North Carolina and the Southeast Gardening

Adams, William D. and Thomas R. LeRoy. The Southern kitchen garden: vegetables, fruits, herbs and flowers essential for the Southern cook. Taylor Trade Publishing, 2007.

Bost, Toby and Jim Wilson. The Carolinas gardener’s guide. Franklin, Tennessee, Cool Springs Press, 2004.

Chaplin, Lois Trigg. The Southern gardener’s book of lists: the best plants for all your needs, wants, and whims. Taylor Trade Publishing, 1994.

Foote, Leonard E. and Samuel B. Jones, Jr. Native shrubs and woody vines of the Southeast: landscaping uses and identification. Timber Press, 1989.

Halfacre, R. Gordon. Landscape plants of the Southeast. Sparks Press, 1989.

Holmes, Roger. Taylor’s guide to gardening in the South (Taylorís Gardening Guides). Houghton Mifflin, 1992.

Holmes, Roger and Rita Buchanan. Home landscaping, Southeast region. New Jersey, Upper Saddle River, Creative Homeowner Press, 1998.

Justice, William S., C. Ritchie Bell, Anne H. Lindsey. Wild flowers of North Carolina. University of North Carolina Press, 2005.
Kraus, Helen and Anne Spafford. Rain gardening in the South: ecologically designed gardens for drought, deluge and everything in between. Eno Publishers, 2009.

Loewer, Peter. The winter garden: planning and planting for the Southeast. Stackpole Books, 1997.

Ogden, Scott. Garden bulbs for the South. 2nd edition. Timber Press, 2007.

Polomski, Bob. Month-by-month gardening in the Carolinas: what to do each month to have a beautiful garden all year. Cool Springs Press, 2006.

Radford, Albert E., Harry E. Ahles, C. Ritchie Bell. Manual of the vascular flora of the Carolinas. Chapel Hill, University of North Carolina Press, 1968.

Southern Living garden book. Birmingham, Alabama, Oxmoor House, 2004.

Tuesday, July 9, 2013

Rain Gardens: Stormwater Management in the Garden

Rain garden in eastern Durham. Photo by C. Chamberlain, Durham Co. Extension Master Gardener. 

Posted on by
By Michelle Wallace, Consumer Horticulture Agent, Durham County

It’s raining – again! Do you wish you could save some of that rainwater for later? Maybe you are tired of seeing your soil and mulch wash down the street during heavy downpours. There are some things you can do.
There are butterfly gardens, children’s gardens, and vegetable gardens – all of which are designed and developed around a central theme. So, what kind of garden is built around the theme of rain? Rain gardens are gardens created to help with stormwater management.
In the past, the goal has always been to manage stormwater by getting rid of the surface water as fast as possible. The water from roads is drained into the city sewer system, where it disappears. With more flooding of streams, creeks, and rivers, everyone is becoming aware of how important it is to manage storm water. In addition, the old methods of managing stormwater did nothing to reduce pollutants from entering our watershed.
It has taken some time, but the old method of managing storm water is changing. Instead of trying to get rid of the stormwater as fast as possible, stormwater is retained and allowed to slowly percolate into the soil. Wetlands and bog plants are used to help filter out the pollutants in the water.
More subdivisions are required to manage their own stormwater. Bio-retention ponds made beautiful with plantings of attractive water loving species become desirable focal points and also increase the bio-diversity of insects and wildlife. Some subdivisions are even doing away with tradition curb and gutters along the streetscape and utilizing drainage ditches, more common in rural areas.
What can you do? To start, consider utilizing the water that falls on your property. If you have gutters, connect the downspouts to a rain barrel or cistern. Cisterns will also solve your water problems during the long dry spells in the summer. They can be attached to an irrigation hose. Another solution is creating a slight depression in your landscape where water can collect and drain. Amend the soil in the depression to avoid standing water for extended periods. Utilize water loving plants that can sustain themselves while submerged in water over a short period of time. Many of these plants are also well adapted to dry periods. There are several plants that will flourish in wet soils including: Hibiscus moscheutos (swamp hibiscus), Iris pseudacorus (yellow flag iris), Baptisia species (false indigo), Lobelia cardinalis (cardinal flower), and Itea virginica (Virginia sweet spire).
For more information on Rain Gardens visit

Wednesday, July 3, 2013

Rooftop Gardens Take Gardening to Next Level

A green roof at the Durham Briggs Avenue Community Garden (L)
and the American Horticultural Society River Farm headquarters (R).

Thinking about creating a green roof on a shed or garage? How do you even begin to install one? What are the benefits?

What plants are best to use, and  most importantly, will they eventually rot the roof?!!

Here is an informative article that answers these questions and many more:

Late blight of Tomato: humid and wet weather perfect conditions!

P. infestans
By Kelly Ivors, Extension Plant Pathologist

Pathogen:  Late blight of tomato is caused by the fungus-like organism Phytophthora infestans.  The pathogen is best known for causing the devastating Irish potato famine of the  1840's, which killed over a million people, and caused another million to leave the country. 
Host crops and plants:  Besides tomatoes,  P. infestans can only infect a few other closely related plants including potato, petunia and related solanaceous weeds such as hairy nightshade.

Host parts affected:  All above-ground portions of the plant.

Symptoms of late blight:  The first symptoms of late blight on tomato leaves  are irregularly shaped, water-soaked lesions, often with a lighter halo or ring around them; these lesions  are typically found on the younger, more succulent leaves in the top portion of the plant canopy. During high humidity, white cottony growth may be visible on underside of the leaf. Spots are visible on both sides of the leaves. As the disease progresses, lesions enlarge causing leaves to brown, shrivel and die (Figure 3). Late blight can also attack tomato fruit in all stages of development. Rotted fruit are typically firm with greasy spots that eventually become leathery and chocolate brown in color; these spots can enlarge to the point of encompassing the entire fruit.
For more information on how to treat late blight of tomato, see