Weed control is often one of the costliest production inputs for container nurseries. We all know that customers are going to want weed-free pots, but probably more important is the fact that weeds can reduce crop growth by more than 50%, extending production times and reducing profitability. All of these reasons make having a good weed management program very important for container growers.

Since there are not many postemergence herbicides that can be used in containers, most growers turn to preemergence herbicides and hand weeding for the bulk of their weed management program. When preemergence herbicides do not work as well as they have in previous years, it is important to understand why. It is common to receive calls from growers who had poor results with an herbicide, but it is a little more difficult to figure out why when the main culprits (calibration, timing, etc.) are ruled out. Interestingly, a common question that came up was what effect does pine bark age have on preemergence herbicide performance? Aged pine bark is the one of the most common organic substrate components in the U.S., with bark from loblolly or longleaf pines being the most prominent in the southeastern U.S. With all that is known about using pine bark substrates, research has not thoroughly evaluated the role of bark age of various crop production parameters. Since very little was known on the topic of bark age and herbicide performance, we conducted a series of experiments, supported by the Horticultural Research Institute, to find out.

Pine bark aging process

Before discussing our experiments and results, it is important to first understand how the aging process affects pine bark. Pine bark aging is not composting (no nitrogen is added) but is conducted similarly in that bark is piled up in windrows, wetted during dry weather and turned periodically to prevent excessive heat buildup and allow for consistent aging of the whole pile (Figure 1). Pine bark (or other barks) may be aged anywhere from six weeks to one year depending upon availability, product demand and/or grower preferences. A detailed description of the aging process and what effects it has on pine bark have been detailed before: nurserymag.com/article/nm1014-pine-bark-variations-differences. Here, we will just focus on the fact that aged bark usually has more fines (typically considered less than 0.5 mm in size), a higher white wood content and usually has a higher water holding capacity (due to the higher percentage of fines).

To further understand the role of pine bark age (aging) on nursery crop production practices, a long-term study was implemented to quantify the changes in the physical, chemical and hydrological properties of longleaf pine bark over the course of one year of aging. Fresh longleaf pine bark (within days of being removed from freshly harvested trees) was hammer-milled and placed in three piles of approximately 250 cubic yards each, with dimensions of approximately 55 x 33 x 10.5 ft. These were treated as replications. Piles were sampled initially, then turned every four to six weeks using a front-end loader, and subsequently sampled after turning for a period of 12 months. At each sample date, subsamples were taken from different locations on each pile to account for variation within the pile and to reduce possible errors due to stratification of constituents and conditions within the piles. These subsamples were combined into one representative sample per pile and tested in herbicide efficacy trials.

Will substrate age affect preemergence herbicides?

The first experiment we conducted evaluated three herbicides including dimethenamid-P (Tower), isoxaben (Gallery SC), and prodiamine (Barricade) on pine bark (previously screened to 0.38 inch) that had either been aged for 0, 4, 8 or 12 months (Figures 2 and 3). The weed species we evaluated included bittercress (Cardamine flexuosa), oxalis (Oxalis stricta) and large crabgrass (Digitaria sanguinalis). We wanted to pair up the weeds with herbicides that usually work very well for control and chose Tower to test oxalis, Gallery for bittercress, and crabgrass for prodiamine. We applied the herbicides at a range of rates from as low as 0.125× the label rate up to 2× the label rate to see if there was any difference in performance and to figure out what rate was needed to achieve acceptable control on each substrate.

Weed counts, biomass, and other data were taken over a 10-week period. While we saw a few differences in substrates at very low rates, we observed consistent weed control across all four substrates when labeled rates were applied. We also looked to see if leaching (downward movement of the herbicide) was affected by substrate age but again, we saw no differences and minimal leaching as would be expected, since these herbicides do not tend to leach significantly.

It is important to note that these experiments were conducted using pine bark that was processed to pass through a 3/8-inch screen. While physical properties were largely similar among the different ages, bark that was aged 8 or 12 months had a higher percentage of fines (and greater water holding capacity) compared with bark that had been aged 0 or 4 months. In other experiments looking at only particle size, we have observed that as particle size increases, weed germination and growth will decrease. This is simply due to greater water holding capacity of the finer particle substrates and because weeds won’t germinate if they are stuck on a large bark particle, or don’t have access to water, similar to reasons why mulch is so effective as a weed control tool (Figure 4). Herbicide leaching also tends to increase as particle size increases. In reality, the bark substrate particle sizes needed to see a significant decrease in weed growth (screened to have all particles larger than 0.25 or 0.38 inches) would not be very conducive for optimal growth of the crop being grown either.

What about other production practices?

Another part of this project funded by the Horticulture Research Institute was to determine what impact fertilizer placement had on herbicide performance. For these experiments, we looked at a range of herbicides applied to containers filled with a pine bark substrate that was fertilized with controlled release fertilizers that had been either top dressed, incorporated into the substrate prior to potting, or were subdressed (which is placing the fertilizer in a single layer about 2 inches below the container surface). While the herbicides tended to perform fairly similarly regardless of fertilizer placement, what was interesting was the weed growth in the containers not treated with any herbicide. Spotted spurge (Euphorbia maculata), eclipta (Eclipta prostrata) and crabgrass growth was 80 to 90% less in subdressed containers compared with containers that had fertilizer top dressed or incorporated. Essentially, what happened was the seeds were able to germinate, but the seedlings had no access to the nutrients due to the subdressing depth and remained very small over a 12-week period (Figure 5). This was promising as subdressing could potentially be used to reduce weed growth in herbicide sensitive plants.

Reasons for poor herbicide performance

If substrate age and fertilizer placement are not playing a major role in herbicide performance, what might be causing variations in performance from year to year? There are many possible explanations, but we will just focus on the most common. First, check to ensure the applicators are applying the correct rate. Calibration errors are the most common reason why I see poor results from preemergence herbicides, especially with granular products that can be more difficult to apply. Making sure the correct rate of a particular herbicide is being applied is critical. Recommended rates for granular products are going to range around 100 to 200 lbs. per acre depending upon the herbicide, so calibrating for each herbicide you use is important. Secondly, did the pots already contain weeds? Waiting too long after potting (more than 3 or 4 days), skipping applications or missing weeds during hand weeding are going to reduce control. While most suppliers keep bark inventories and areas around the facility very clean (Figure 6), some may have weed problems that could rear their head at your nursery. Applying a preemergence herbicide soon after potting could help alleviate this issue if it occurs with a current shipment. It is also important to pick herbicides that are effective for your particular weed spectrum and regularly rotate modes of action. The 2017 Southeast Pest Management Guide (http://bit.ly/SE-Nursery-Pest-Control) contains a comprehensive list of efficacy rankings for different herbicides and what ornamentals they can be used on (among a lot of other great information for other pests). Sanitation is also critical whether that be around bark piles, roadways, aisles, ditches (Fig. 7 Weeds near bark piles). Lastly, weather can play a big role. Frequent and high rainfall can reduce the longevity of these herbicides and could require sequential applications to be made a little earlier than expected in some cases.

While herbicides will likely perform similarly regardless of substrate age, pine bark aging can have a significant effect on air space, water-holding capacity and total porosity, which can affect irrigation, needed amendments, etc. Bark properties can even change from the same suppliers depending upon the time of year and from batch to batch, so routine testing would still be recommended.

About the authors: Dr. Chris Marble is an assistant professor in ornamental and landscape weed management and specializes in invasive weed management at the University of Florida, marblesc@ufl.edu . Dr. Brian Jackson is an associate professor and director of the Horticultural Substrates Laboratory at North Carolina State University; Brian_Jackson@ncsu.edu.

An international movement has embarked on a mission to create cities where “people and nature are better connected.” The National Park City Foundation (NPCF) is working toward cities “rich with wildlife, where every child and young person benefits from exploring, playing and learning outdoors. Cities where we all enjoy high-quality green spaces.” Sounds like Utopia, eh? It’s not a bunch of lip service. In 2019, the NPCF named London the first National Park City. Half of London’s area is considered “green” (trees, parks and green roofs) or “blue” (rivers, canals and reservoirs).

This designation helps in three key areas:

1. Connect more people to nature and the outdoor culture, improving health, well-being and social cohesion.
2. Create more high-quality green and blue space, making London over 50% green (nature) and blue (water), delivering improvements for wildlife, people’s enjoyment and an attractive and sustainable environment for visiting, living and working in.
3. Promote London’s identity as a National Park City. Help residents and visitors to appreciate its value and potential for a rich cultural life anchored in its outdoor heritage.

The NPCF expects this designation will create a greater diversity of natural wild spaces, improve air quality and the standards of everyday life for residents and visitors. Children and adults will enjoy play, recreational and learning experiences outdoors, with a positive impact on physical and mental health. More planted and green space will reduce flood risk and increase resilience, as well as enhancing its biodiversity. The group expects that London will become more distinctive as a city, attracting more visitors, investment and interesting activities and businesses of all kinds, boosting its economy and its global brand.

A project of this magnitude requires private/public partnerships, money and willing citizens. In London’s case, the mayor earmarked £9m to support National Park City activities and aligned policies to the NPCF, including matching its target of making 50% of London physically green.

As we enter a new decade, cities in the U.S. should use the National Park City principles as a guide to create more celebrated and mandated green spaces. The green industry could be front and center in such a high-profile project. Find out more about NPCF and the London National Park City at nationalparkcity.london.

It is a rare occurrence that a new tree species is discovered on our green and blue planet. Such was the case in 1999 when a new conifer was discovered by botanists in the mountains of northern Vietnam. This tree was originally placed in a new genus all its own, Xanthocyparis, and was given the species name vietnamensis. DNA studies in 2010 reclassified it in the genus Cupressus, sub-genus Xanthocyparis. Sadly, the tree is critically endangered in its native habitat due to the fact that its aromatic wood is prized by local people to build shrines and coffins. There are perhaps fewer than 1,000 trees left in Vietnam, and only a handful of mature specimens capable of reproducing from seed. More recently in 2014, a small population of C. vietnamensis was found in the Guangxi Province of China, giving hope that it can reproduce in the wild. Efforts are being made to protect remaining trees in Vietnam. I like the idea that bringing this tree into cultivation will help save it from extinction.

is a beautiful tree in the landscape and has great potential in ornamental horticulture. When I first saw one in a garden setting at the Rhododendron Species Botanical Garden near Seattle, Washington, I thought it was a species of Cunninghamia because the juvenile foliage resembles the China fir at first glance. The transitional and adult foliage is much more cypress-like, and this foliage plurality is an attribute that makes the tree visually interesting. The common name of C. vietnamensis is Golden Vietnamese Cypress, and the golden color becomes more pronounced as the tree matures and its adult leaves receive more direct sun. The most reliable references I have talked to consider C. vietnamensis to be hardy to USDA Zone 8, though a couple indicated that the zone has the potential to go lower, perhaps Zone 7. The introduction of the plant into select North American gardens came in 2006 when an expedition to northern Vietnam sponsored by the Elisabeth C. Miller Foundation returned with cuttings.

Why grow Cupressus vietnamensis?

• It has eye-catching blue-green juvenile and adult foliage forms growing concurrently.
• It’s very rare in both the wild and in cultivation, adding to its perceived value.
• It’s relatively easy to grow in commercial horticulture.
• Growing this tree helps protect it from extinction.

If you looked only at the big picture, you’d have to say we live in deeply troubled times. It seems we’ve never been more polarized. Political discourse feels more like a war zone than a thoughtful national conversation. But what happens when you zoom in closer?

That’s the question I ask myself as I reflect on the past year spent exploring dozens of small and mid-sized communities across America. I’ve talked with hundreds, maybe thousands, of mayors, chamber of commerce members, new entrepreneurs, business owners and citizens of all ages. I’ve sat down to great meals in downtown restaurants, listened to fabulous bands and attended some of the world’s coolest festivals. And what I’ve found is that the America one sees “up close and personal” bears little resemblance to the America one sees on the national news.

I’m not saying we don’t have real problems. We do. But we have more bright spots than dark — more courtesy than incivility — and often that good news flies under the radar. I’ve always been a believer in shining a light on the positive until it overcomes the negative. Gratitude is more powerful than griping. And what I’m grateful for today, at the turn of the year, is America’s communities.

Real life doesn’t happen nationally. It happens locally. And at the community level, I see people partnering with their neighbors to solve problems, working hard and playing hard, listening and compromising and — quite often — making sacrifices for the good of others. Locally is where we’re at our very best. It’s where we can use our influence and our gifts to make our communities strong and to make life better for everyone.

I view communities through a lens of revitalization because that’s the work I do. As things have gotten more dysfunctional at the national level, the by-product is that people on the local level have kicked in. And what I see is that citizens aren’t counting on government to “save” them. They’re doing the hard work of revitalization themselves. They’re owning it. They’re investing in their cities and towns. And they’re starting new conversations: How can we make our community the best it can be? How can we reinvent ourselves, start and grow local businesses, and transform into a great place to work, live and play?

This mindset has kicked in everywhere: big cities, small towns, communities of every shape and size. And no wonder. The chaos and uncertainty of the past few decades have made us crave personal connections with our friends and family. We want our children and grandchildren nearby (with good jobs to keep them there). We want lively downtowns with great restaurants, funky stores, cool living spaces and plenty of fun things to do. And we’re making it happen.

In Thomas L. Friedman’s book “Thank You for Being Late: An Optimist’s Guide to Thriving in the Age of Accelerations,” he talks about how rapid accelerations in technology, globalization and Mother Nature are disrupting our lives and leaving people feeling destabilized. He says these forces are like a hurricane, one in which the winds of change are swirling so fast that families can’t find a way to anchor themselves.

Friedman makes the case that the only answer is building healthy communities, ones that are flexible enough to navigate this hurricane and provide stability for the citizens within them. He quotes the words from a ballad by Brandi Carlile, “You can dance in a hurricane, but only if you’re standing in the eye.” Our communities are that eye. They provide a firm place to stand and find stability while all this change is swirling around us.

My hope is that 2020 will be the Year of the Community. We can make it so. We can hold our families close. We can reach out to neighbors to connect with them, to help them, to engage them in the work of making things better. We can shop local. We can partner with government the right way. We can smooth the way for entrepreneurs. We can galvanize our small business communities to drive positive change. And we can act as ambassadors for our communities so that others want to invest, live, work and play here too.

Won’t you join me? Celebrating all the good in our communities, and working together to make them stronger, will make for a 2020 that’s even better than all the years that have come before.