Your car has a gas gauge to help you avoid running out of gas. Many newer cars can even tell you how many miles you can go before you run out of gas. Do you know how much water is in your reservoir and how long that water will last without a refill? Do you know how much water is returning to your reservoir after you irrigate or when it rains? We have developed some user-friendly tools to help you better understand some of these components of your irrigation system.

This article is the first in a series of four where we will explore 10 free online tools designed to help you understand different aspects of water use and reuse at your nursery operation. These tools and many other resources can be found at www.cleanwater3.org. This site has a wealth of information for container plant growers and is a great place to go for research-based information.

In this article, we will be discussing three tools: a reservoir volume calculator, an irrigation volume calculator, and a reservoir refill calculator. Alone and in combination, these tools can help you better understand the availability of your water resources.

Reservoir volume calculator

Continuing the gas tank analogy, your reservoir is the “tank” that stores water for irrigation when needed. Knowing the reservoir’s capacity or how much water it holds at any given time are important pieces of information. This tool provides you with an approximation of the maximum volume your reservoir can hold. Once you have this information, we will show you some ways that you can use it.

There are three ways that you can enter information about your reservoir’s surface area.

Enter the surface area of your reservoir directly, if known (“Enter Area” button, Figure 1 [A]).

Use the map feature to locate your reservoir(s) on a map and automatically calculate the surface area (Figure 1 [B]).

Enter the average dimensions, either width and length or diameter (Figure 1 [C]).

For all three options, check to ensure that the units (acres, square feet, etc.) correspond to the values you entered. The units can be changed by clicking on the box for a drop-down menu of available options.

After you enter the reservoir surface area, the only other piece of information needed is the average reservoir depth (above your pump intake). Once you click “compute volume” the estimated volume will be displayed. You can change any of the units to ones that make sense to you. Knowing the maximum reservoir volume will help you to better understand how much water you have available and in reserve for your irrigation needs. The next tool that we will discuss should help put this into perspective.

Irrigation volume calculator

Now that we know the maximum water holding capacity of your reservoir, it’s time to determine how long that water will last when it is used for irrigation. The irrigation volume calculator can be used to determine how much water is used during an irrigation event for individual blocks or your whole operation. You can use this tool to evaluate current water usage, when you are considering changing irrigation types/heads, or when expanding your operation.

Step 1. Begin by clicking on the “Add irrigation system” button and click on one of the four types (impact, wobbler, spray, or drip. See Figure 2).

Step 2. Fill in the information for the first production block (see Figure 3) making sure that the units are correct (gallons per minute versus gallons per hour, etc.).

Step 3. Repeat steps 1 and 2 as needed to add additional production blocks. If you have similar irrigation systems, you can copy them and then adjust as needed. For example, if you have one block that has 40 heads and one with 60, but they are otherwise the same, you can copy the one block and change the number of heads for the second one. As you add more blocks, you will be shown the amount of water that each block uses, as well as the total volume of water applied per day.

If you adjust the number of cycles per day or minutes per cycle during different seasons, you can easily calculate how to adjust your irrigation volume. You can label the irrigation blocks to make things easier to remember, and delete them if you make a mistake (see Figure 3). You can add as many irrigation blocks as your operation needs.

Once you have all of your irrigation blocks added, you can take your reservoir capacity and divide it by the total volume of water used for irrigation each day. Let’s say that your daily irrigation total is 125,000 gallons, and you have a reservoir capacity (from the reservoir volume calculator) of 1,630,000 gallons. That means that you have 13 days’ worth of irrigated water in your reservoir if it is not refilled. Furthermore, these two tools could be used to determine the impact of expansion on daily irrigation volume and reservoir capacity if you wanted to expand your operation.

Reservoir refill calculator

If you collect your irrigation return flow water and reuse it at your operation, that’s great! But how much of your irrigation water actually makes it back into your reservoir? This question does not have an easy answer since it is based on a number of factors, but the irrigation reservoir refill calculator can help give you an educated estimate. You can use this calculator to help determine how much water is returning to refill your reservoir.

These tools can be used to help you understand your operation’s current water status and also help you plan for the future.”

Water can flow into your reservoir from both irrigation return flows and rain water. So, you must first decide whether you want to know how much (1) rainfall or (2) irrigation water is returned to your reservoir. The volumes of water from irrigation return flow or l generated rainfall are different because irrigation is only applied to production areas and rainfall occurs everywhere (production areas, roads, etc.).

Whether the water is from irrigation or rainfall, the land surface is on which the water falls is called the “contributing area” (Figure 4 [A]). The “irrigation/rainfall depth” is how much water is being applied over the contributing area. One way you can calculate irrigation depth is to divide the volume applied (from the irrigation volume calculator) by the irrigated area. If the same unit for volume and area are used (i.e., cubic feet and square feet), no conversion is necessary. But if different units are used (i.e., gallons and acres), you will need to convert to depth. This can be done for gallons per acre by dividing the result by 27,150 gallons per acre inch. For example, if you calculated that you applied 150,000 gallons of irrigation to 7 acres of land.

This depth of irrigation/rainfall is entered into the “Total Rainfall/Irrigation Depth” box in the calculator (Figure 4 [B]). Ensure you enter the correct time (the duration of the irrigation event) corresponding to this depth box (Figure 4 [C]). Rainfall or irrigation volume intensity (precipitation rate) and infiltration rate both affect how much water returns to your reservoir. If the rainfall or irrigation volume intensity is less than the infiltration rate of the surface, no runoff will be generated. Conversely, as the rainfall or irrigation intensity become greater than the infiltration rate, more stormwater or irrigation return flow will be generated. A perfect example of this is a high intensity rain for a short duration that fills up streets and gutters quickly. For example, adding an inch of water over 30 minutes will produce more runoff than an inch over 60 minutes.

Adobe Stock

You also need to enter the average overall slope of the contributing area and the surface type (Figure 4 [D]). Choosing your surface type can be challenging if you have multiple surfaces. You can either choose the one that represents the most dominant surface (for example your production areas) or calculate each area separately. Impervious surfaces (asphalt, concrete, greenhouse, etc.) will return all of the water to the reservoir, while the different soil types, rocks, and fabric will all return a portion of the water to the reservoir. We will caution you that the value you receive for the volume of water returning to your reservoir is an ESTIMATE, since there are a number of factors that can affect the volume of water that is returned to your reservoir. If you get stuck, we’ve developed a short YouTube video for each tool to help you get information tailored to your operation with ease and confidence.

These tools can be used to help you understand your operation’s current water status and also help you plan for the future, whether you are thinking of expanding your operation or ensuring you have adequate water reserves when adverse conditions happen. We hope these tools help you understanding how much water you are storing and applying at your operation. Our next article in this series will provide you with practical tools for measuring your irrigation efficiency.

About the authors: John Majsztrik is a research assistant professor at Clemson University, jmajszt@clem son.edu; Bruno Pitton is a staff research associate in the Department of Plant Sciences at the University of California, Davis, bjpitton@ucdavis.edu; Lorence Oki is a cooperative extension specialist at UC Davis, lroki@ucdavis.edu; and Sarah White is a professor and nursery extension specialist at Clemson University, swhite4@clemson.edu.

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.