Nursery Knowledge: What’s in the Pot?

Exploring Stratified Substrates and Soil Hydraulics in Agricultural Science

Lloyd Nackley

Nursery science researchers have embarked on a journey to harness the principles of soil hydraulics to reshape container production practices. In the past couple of years, Dr. Chris Criscione and Dr. Jeb Fields and others released a series of articles that showed that stratifying pine bark can serve as a substitute for peat-based media in floriculture and bark-based woody plant production. Through layering premium floriculture media over cost-effective pine bark within containers, they reduced reliance on peat. In their study focused on Petunia hybrid ‘Supertunia Honey’, the stratified substrates yielded crops of comparable size and quality, along with enhanced root productivity. Their work also showed superior performance of bark:coir substrates in a stratified setup, even when subjected to reduced irrigation when producing Loropetalum chinense ‘Ruby’ liners. Positive microbial communities in stratified systems further aided in mitigating water stress. Furthermore, Red Drift® rose plants grown in stratified substrates exhibited equal or superior crop growth despite receiving less controlled-release fertilizer. This suggests potential for reducing fertilizer and irrigation rates while upholding crop
quality, offering a sustainable avenue for containerized crops. This blog post aims to shed light on stratified substrates and also provide insights into ongoing projects at the Nackley Lab that are delving into this innovative frontier of nursery science.

image shows containers of growing medium of different textures
Image: mixing coarse and fine substrates in containers to address soil stratification

Soil hydraulics delves into the intricate world of water movement within soils—how water traverses the soil matrix, its distribution, and its intricate interactions with soil particles and structure. It’s a field dedicated to understanding the physics governing water’s journey through soils, and this knowledge carries significance for agriculture, environmental science, hydrology, and civil engineering. Soil hydraulics guides irrigation strategies, shapes drainage designs, and fuels sustainable land management practices.

image shows saturated and unsaturated soils in comparison
Image: water in saturated and unsaturated soils

Central to soil hydraulics is the concept of matric potential, a critical factor in irrigation management and plant-available water. Matric potential captures the degree to which soil particles retain water due to molecular attractions—it’s essentially the “stickiness” of water to soil particles. When soil isn’t completely saturated, minuscule air-filled spaces exist between particles. Water molecules adhere to these particles, creating capillary forces that coax water upwards. The strength of the bond between water and soil particles determines the matric potential, effectively influencing water availability to plants.

Image shows layering of the 3 soil phases: gaseous, liquid and solid
Image: the gaseous, liquid and solid phases of soils

Two other essential players in the realm of soil hydraulics are soil texture and structure. Envision soil as an intricate mosaic, with particles coming together to form aggregates, shaping distinct pathways and chambers. This arrangement, referred to as soil structure, creates macropores—
akin to express highways—through which water can flow rapidly. At the same time, micropores, reminiscent of narrow alleyways, gently retain water against gravity’s pull, acting as reservoirs
for plant roots during dry spells. Additionally, soil structure influences permeability, determining how efficiently water infiltrates and the risk of surface runoff.

Soil texture, on the other hand, hinges on the proportions of sand, silt, and clay particles in the soil. Each particle type comes with distinct traits that shape water dynamics. Coarser-textured soils with more sand have ample space between particles, allowing water to move quickly with
less retention. Finer-textured soils, rich in silt and clay, boast smaller gaps between particles, leading to slower water movement and higher water-holding capacity.

image shows the soil texture triangle
Image: The Soil Texture Triangle

However, when soil is confined to pots or containers, it undergoes transformations in its natural structure due to various container-related factors. The restricted space of a pot, contrasting with the expanse of natural soil, can lead to the erosion of soil structure. Aggregates—clusters of particles forming pores and pathways—can deteriorate over time due to limited expansion room. This confined space often results in compaction, where soil particles compress closely, reducing essential air-filled pores needed for root growth and water movement. The watering practices specific to potted plants can contribute further by compacting soil particles as water occupies gaps. The absence of natural soil organisms and plant roots within containers hampers the
maintenance of soil structure. Repeated disturbances, like transplanting or repotting, can exacerbate these structural changes. To counter these effects, selecting appropriate potting mixes that retain structure, incorporating organic matter for improved aeration and water retention, and being mindful of compaction during planting and watering are recommended.

image shows a hydrangea in a pot with drip irrigation
Image: Hydrangea in pot with drip emitter irrigation

Traditionally, the nursery field has focused on creating homogeneous potting mixes that maintain structure while offering suitable hydraulic properties. Classic blends often comprise bark, coir, peat, perlite, vermiculite, and pumice. However, a recent shift in focus has led scientists to explore how layering media can simulate natural soil hydraulics—an approach known as stratified substrates.

coarse substrate
Coarse substrate
fine substrate
Fine substrate

Stratified substrates involve arranging potting media of varying textures in layers within a single container. This structured layering entails placing coarser-textured substrates at the bottom and finer-textured ones on top, mimicking natural soil layers. This technique aims to influence water
movement, nutrient distribution, and hydraulic behavior within the confined environment of a container. By borrowing from the stratification seen in the ground, stratified substrates strive to
optimize resource efficiency, plant growth, and root development in controlled settings like potted plants.

Some may draw parallels between stratified substrates and the practice of placing rocks or gravel at the bottom of larger plant pots. While both concepts involve layering materials, there are distinctions. The practice of adding gravel or rocks to enhance drainage in larger pots shares a
kinship with stratified substrates. However, it doesn’t replicate the comprehensive layering dynamics seen in stratified substrates. Adding gravel mainly addresses drainage concerns without fully incorporating the layered hydraulic principles inherent to stratified substrates.

image shows 2 piles of substrates by texture
Image: fine (l) and coarse (r) substrate, side by side

Dr. Chris Criscione, in collaboration with the Dr. Jeb Fields group at Louisiana State University, has been at the forefront of investigating stratified substrates in containerized plant growth. Their research delves into how layering different potting media textures can enhance water retention, nutrient availability, and overall plant performance. The studies highlight promising outcomes, such as heightened root productivity, improved growth, and enhanced quality under stratified
conditions compared to conventional substrates. This technique holds potential for bolstering sustainable crop cultivation within controlled environments.

gravel pad with pots of hydrangea growing
Image: potted hydrangeas on the gravel pad at NWREC

Nevertheless, it’s crucial to acknowledge that findings from studies conducted in one geographic region—such as the Southeastern USA—may not seamlessly extrapolate to other areas with distinct climates and environmental conditions, like the Pacific Northwest. Climate, temperature, humidity, and other factors can significantly influence plant growth and water dynamics. Given this variation, research in regions like the Pacific Northwest, such as Oregon, is crucial. The
unique environmental factors there, including cooler temperatures and higher rainfall, can impact water movement, nutrient availability, and plant response to stratified substrates. Bark-based substrates, common in some areas, may behave differently in terms of water retention and
drainage in regions with distinct soil compositions. To address this, the Nackley Lab initiated a collaboration with Dr. Fields and others in 2022, planning to explore the impacts and benefits of stratifying substrates in Nursery production. The first stratified substrate experiment was
launched in 2023 at Oregon State University North Willamette Research and Extension Center (NWREC), aiming to reduce resource demand and provide insights into the effectiveness of stratified substrates in that context, contributing to more informed decision-making for nursery production and horticulture practices in the region.

More Information:

Evaluating Stratified Substrates Effect on Containerized Crop Growth under Varied Irrigation Strategies

Root Exploration, Initial Moisture Conditions, and Irrigation Scheduling Influence Hydration of Stratified and Non-Stratified Substrates

Single-screen Bark Particle Separation Can be Used to Engineer Stratified Substrate Systems

Stratified Substrates Can Reduce Peat Use and Improve Root Productivity in Container Crop Production

Meet the Team: Summer Update

The Gravel Pad update you’ve been waiting for, and more!

There’s so much going on in the season of plenty around NWREC! Enjoy this virtual tour of a few projects around the nursery.

Dalyn has been continuing her work with mini-lysimeters that control irrigation in shade trees – these tiny scales weigh the potted plants and use the change in weight as they dry to determine when to turn on the water. The lysimeters are gathering data on plant weight along with an on-site weather station to better understand the relationship between heat and irrigation in gravel pad production. Read more about this project here.

View of gravel pad with potted maple trees
Young red maple trees on the gravel pad are using lysimeters to monitor water loss in conjunction with a dedicated weather station (left).

The Willamette Valley has had a few HOT summers in a row, even though lately this one has been pretty mild. Nevertheless, we haven’t given up on finding solutions for heat mitigation – including growing ornamentals under drought conditions to see which are the most “climate-ready” to meet changing needs. We’ll be asking the public to evaluate those plants in the upcoming Climate-Ready Field Day, come along and see how the plants are progressing (click the link above for more info).

In addition, we’re evaluating different means of mitigating the heat and the resultant high rates of evapotranspiration (basically ways to reduce plant sweat), from misting the young plants to covering tissues with kaolin, introducing fungicides that may be beneficial in managing water loss, using white pots instead of the traditional black, and even growth inhibitors – it’s been a pretty amazing feat to monitor the effects as you can see- check out this monitoring station!

Jaiden, Lloyd and Dalyn at the ET monitoring station with shade trees
Dalyn, Lloyd and summer hire Jaiden show off the monitoring station in the heat stress/evapotranspiration mitigation study.

young flowering shrubs in alternating black and white pots
Does the color of the pot change the heat stress for these water-loving shrubs on the gravel pad?

A small project growing marigolds for festivals and holidays – like Dia de los Muertos – is also underway. Growing the marigolds has certainly brightened up the Nursery Zone at NWREC, and we’ve progressed into evaluating passive means to dry the flowers, saving energy and resources while preserving the gorgeous summer color.

fresh marigolds
Marigold blooms
dried marigolds

There’s even more in the works – stay tuned for information about fall workshops and PACE courses created specifically for nursery and greenhouse production for topics covering drone sprays, integrated pest management, and more.

Climate-Ready Landscape Plant Field Day 2.0

UC Davis Plant Trial Field Day 2020
Photos: UC Davis Plant Trial Field Day 2020 cr: Karrie Reid

Who should attend: Professionals from landscape, horticulture, nursery and related fields; OSU Master Gardeners; garden writers; academics/educators

When: August 17th 2023; 10am – 2pm (Arrive when convenient; ratings take about 60 min)

Where:                  OSU’s North Willamette Research & Extension Center

15210 NE Miley Rd, Aurora, OR 97002

What’s involved: Evaluating aesthetic qualities of selected landscape plants (about 60 minutes).

Photos: UC Davis Plant Trial Field Day 2020 Credit: Karrie Reid
Photos: UC Davis Plant Trial Field Day 2020 Credit: Karrie Reid

About this Event

The ever-changing climate iputs pressure on the industry to develop more sustainable plants. As part of a six-university study, OSU seeks to improve urban water-use efficiency by evaluating landscape plant performance on three irrigation treatments corresponding to the Water Use Classification of Landscape Species (WUCOLS): High, Moderate, and Low categories of water need. The plants are irrigated regularly during their first summer after planting. Treatments are imposed during the second growing season where researchers collect growth and quality ratings.

The Field Day allows landscape, nursery, and horticultural industry professionals and educators the opportunity to see new plants in their 2nd year and share your opinions and preferences by rating a representative sample of the plants in the field undergoing irrigation treatments. One plant from each of the 3 water levels, for 15 different species (some released to the public and some not yet) will be surveyed. Along with this field of 360 plants, you will be able to get a sneak peek at the next year’s field, currently in an establishment phase.

Important Details: The fields are packed dirt/uneven mulch, sturdy comfortable shoes, sunscreen and/or a hat are suggested. At the trial site, you will be provided a ratings sheet, clipboard, pen, and given general instructions when you arrive. It is a self-guided tour among our 720 landscape plants. Lots to look at but only a small sub set to evaluate. Hot Coffee and cold water will be provided. We value your feedback and hope to see you there!

**No Registration Needed**

For questions contact:

Lloyd.Nackley@OregonState.edu

Meet the Team: WINTER UPDATE

Lloyd Nackley

At the Western Region International Plant Propagators Society (IPPS), the Pacific Northwest Insect Management Conference (PNWIMC), and the Orchard Pest and Disease Management Conference (OPDMC) last month, we presented cutting-edge research and advancements in our field. Our presentations at the Western Region IPPS and PNWIMC focused on the latest developments in sensor-controlled irrigation, and flatheaded borer management, respectively.

Dr. Melissa Scherr Presents at the PNWIMC in Portland

At the Orchard Pest and Disease Management Conference, we discussed the latest techniques in IPM for managing powdery mildew with biological fungicides applied by our laser-guided Intelligent Sprayer system. Through our presentations at these conferences, we aim to advance the knowledge and understanding of plant health in our field and to promote collaboration among professionals. By sharing our research and engaging in discussions with our peers, we strive to advance the science of horticultural production to support the growth and success of the horticulture in the Pacific Northwest region.

Grower tour visits the olive grove
The buses meet our Horticulture Team at NWREC

At NWREC, we have been working on our new hydroponic greenhouse project. However, since October we have encountered construction challenges in connecting the natural gas heaters, which has impacted the growth of crops such as lettuce, tomatoes, and cucumbers. As a result, lettuce growth has been slow and plagued by Botrytis, and warmer-growing crops like tomatoes and cucumbers have fared even worse. We are working to resolve the permitting issues with the heaters as soon as possible and look forward to updating you on the progress of the greenhouse project in the coming year.

Meet the Team: Unmanned Aerial Systems

Sadie Keller

Unmanned Aerial Systems applications in agriculture have interested me from the time I saw some trial flights at the World Ag Expo in Tulare, California in 2020. The possibilities of crop mapping, using multispectral imagery to create NDVI data, and optimizing resources seemed
endless. And while all of this is still true, I have learned over the last couple years that there is a lot more to it than just getting out the drone and flying it over a field.

Dalyn McCauley, captured in a 2022 drone image

In the Fall quarter of 2022, I was able to take a class on campus from Dr. Michael Wing called “Unmanned Aerial Systems Remote Sensing. In this course I was able to get some hands-on experience flying a DJI Phantom 4, a DJI Matrice 200, and a DJI Matrice 300. We also were able to take aerial imagery with a MicaSense Altum multispectral and thermal camera attached to the DJI Matrice 300 and analyze that data during the course of the class. To analyze the data we learned how to use AgiSoft Metashape photogrammetry software to make orthomosaics of our area of interest. With the orthomosaics, we were able to perform different sorts of analysis using ArcGIS Pro software and R. This class really gave me a solid introduction to the collection and analysis of aerial imagery.

DJI matrice 210 with a zen muse xt2 camera flying over red maples
The DJI matrice 210 with a zen muse xt2 camera flying over red maples

With some knowledge under my belt after taking that course, I decided to look into taking the Part 107 Certification exam to obtain my FAA administered Remote Pilot License. The purpose of this certification is to be able to fly a drone for commercial, government, or any other non-
recreational purposes. In the Nackley Lab, we have access to a DJI Matrice 210 quadcopter and a MicaSense Red-Edge M camera so I wanted to be able to open up some more avenues for research by being able to pilot this drone for our lab!

DJI matrice 300 with a micasense altum camera
DJI matrice 300 with a micasense altum camera

In our lab, a lot of our work centers around major challenges to the nursery production industry in Oregon. Working with a drone can allow you to survey a large area for early signs of drought stress, nutrient deficiencies, or pests to minimize a loss in yield. Now that I have the Remote Pilot Certification, my goal is to help our lab create more aerial imagery (data) that ties into our work which addresses major challenges to nursery production in Oregon like irrigation application, pest management, plant nutrition, and climate adaptations.

Thinking about getting a Remote Pilot Certification? Here are Sadie’s tips for Studying (click here).

For more information about the part 107 certification or UAS applications feel free to contact me
@ kellesad@oregonstate.edu.

Other great OSU resources:
BEAV UAS Program – Dr. Kristine Bucklin and Dr. Lloyd Nackley
Aerial Information Systems Laboratory – Dr. Michael Wing

Plant Health: Sensor-controlled sprayers for specialty crop production

NEW PUBLICATION!

Recently our own Brent Warneke wrote another great article for Sprayers 101 covering the Intelligent Sprayer System – check it out here: https://sprayers101.com/airblast-sensors/

Want a preview? Here’s a synopsis:

Air-blast sprayers are versatile, reliable, and can be modified to fit numerous types of crops, all of which are reasons for their continued popularity. Yet despite their popularity, air-blast sprayers have long had a reputation for inefficient application characteristics. Sensor controlled spray systems reduce labor costs and pesticide waste. Recently, they are receiving renewed interest as their reliability has improved and more options have become available. There are two main types of sensor sprayers:

+ On/off sensor sprayers
+ Crop adapting sprayers

 A classic low-profile axial airblast sprayer.
 A classic low-profile axial airblast sprayer.

Sensor types
Infrared sensors: The inability to resolve characteristics of plant structure makes IR sensors suited to less complex applications such as triggering
the sprayer on and off at a plant. Additionally, these systems can be used for herbicide sprayers where the sensors are aimed at the trunks of trees/vines and turn off the sprayer as they pass the trunk or to target it for the purpose of sucker sprays.

Ultrasonic sensors: using multiple sensors, it’s possible to collect canopy volume data with similar accuracy to taking manual measurements. These are typically used on canopy sprayers with around 3 sensors per side of the sprayer.

Laser sensors (LiDAR): Provides the most accurate measurements of plant structure (mm resolution). Only one sensor needed for accurate measurement.

Plant fluorescence sensors: These have a spatial resolution between ultrasonic sensors and LiDAR sensors. Most commonly used on “weed-seeing” herbicide sprayers but also on canopy sprayers. All sensor sprayers must have a speed sensor to synch the sprayer ground speed to the sensor system.

Spraying with sensor sprayers
Insect pest and disease control with sensor controlled sprayers has
been widely shown to be similar to that of standard sprayers. Control can be achieved on those crops with spray volume savings from 20-70% depending on the sensor system used and crop spray volume savings are higher in crops with more variability labor savings, less pesticide release into the environment, tractor wear, and driver fatigue are also reduced as the sprayer is in operation for less time.

Sensor sprayers can result in 20% to over 90% less spray drift. Autonomous sensor sprayers companies are currently developing and selling autonomous sprayer units that drive themselves and can be integrated with sensors.

Illustration of on/off sensor sprayers (A) and canopy adapting sensor sprayers (B). Sensors are illustrated with red ovals and sensor field of view illustrated with grey shaded washes.

Meet the Team: The Bounty of a Season

Success in Summer 2022

For the past few years we’ve limited gatherings on the farm due to COVID-19 restrictions. In the summer of 2022, however, we were finally able to welcome the public back for Nursery Program Field Days. We’d like to take this opportunity to boast about a few of our highlights from the last several months.

Sadie Keller presenting to growers
Sadie Keller discusses shade tree physiology

For the first time, the Nackley Nursery Production team was an official stop on the Oregon Association of Nurseries Farwest Innovative Production Grower Tour. Our portion of the tour at NWREC showcased sensor-controlled irrigation, heat-stress mitigation techniques, LiDAR smart-sprayer systems, and practices that can reduce boxwood blight spread, and methods of scouting and monitoring insects in nurseries and greenhouses. These projects offer a wide range of savings for growers.: up to 80% improvement in irrigation efficiency, up to 70% reduction in sprayed pesticides, and a significant reduction in boxwood blight infection.

image shows participants examining landscape plants
Stakeholders evaluating climate-readiness of various landscape ornamentals

The second big event was an open house for our Climate Ready Landscape Plant trial, the largest coordinated landscape plant irrigation trial in the Western US. Plant professionals from around the region came to rate plants and discuss how we, as a society, are going to maintain healthy landscapes while faced with increasing extreme weather.

Ongoing projects that will continue this year include, research by our graduate student Sadie Keller, who is investigating Oak and Maple drought tolerance. This summer, Sadie shared her preliminary findings with scientists at the American Society for Horticultural Science, in Chicago.

Sadie Keller and Lloyd Nackley at the ASHS Meeting in Chicago.

In addition, Dr. Melissa Scherr continues our research on the Pacific Flatheaded beetle, with the anticipation of a grower event hosted at NWREC discussing current research on Flathead Borer biology and control this coming April – 2023.

The Nursery Program Team, summer 2022.

Meet the Team: From Hiking to Horticulture

Scout Dahms-May

I am originally from the great city of Tacoma, Washington. I went to an outdoors based high school where my love for plants and environmentalism blossomed. My favorite class was our version of “PE”, where we hiked through Point Defiance Park identifying native species. This passion drove me to pursue a bachelor’s degree in Environmental Science at the University of Redlands. Moving to Redlands in Southern California was a stark contrast to my home in Puget Sound, but I grew to love most parts of it!

Scout collecting samples
Scout collects samples

I went on many abroad terms and saw amazing parts of the world such as Peru, Ethiopia, and Iceland. Each time I returned I wished I had been there longer and itched to immerse myself even more in a different country.  Once I graduated from Redlands, the natural next step was to join the Peace Corps. I spent two years in the Southeast corner of Senegal, West Africa. I lived in a 100-person village in the region of Kedougou where I learned to speak Jaxanke. As an Agroforestry Extension Agent, I helped with various agriculture and agroforestry projects.  We created small-scale nurseries, collected seeds, showcased new and improved agroforestry techniques, and outplanted trees and shrubs around the village. I loved my time in Senegal and miss being there constantly.

After returning to the United States, I moved to Eugene, OR to work at Dorena Genetic Resource Center. I assisted the lead horticulturist in end-to-end native plant restoration, collecting/processing seed, and producing native plants to restore areas affected by fires, floods, and construction. I became the lead irrigator, which was a new problem-solving and damp adventure, and led seed collection trips across Oregon. I also helped develop a seed collection mapping application to track plant populations and store seed collection data.

This leads me to OSU! I just started at OSU this fall to pursue my Masters in Horticulture and work in the Nackley Lab. I am partnered with Sadie Keller on a project looking at stem hydraulics and how it relates to drought in shade trees. I am new to this type of research but am so eager to learn more! I am excited to get our stem hydraulics lab up and running and start the journey of data collection.

2022 Field Day Tour and Open House

August 23, 2022

Nackley Lab nursery production open house takes place August 23. 2023 from 11am – 2pm

Our event will be a part of the great Nursery related activities happening around the Willamette Valley as part of the Oregon Association of Nurseries Farwest Show, which will also feature Dr. Nackley, and Brian Hill, M.S. and many others from Oregon State and beyond.

The Nackley lab open house will feature research on our four themes: Irrigation science, pest management, plant health, and plant trials.

Free to all, no registration required.

Parking: follow signs to south side of the Cravo North Willamette Research and Extension Center and then follow signs walk 5 mins (west) to Nackley Lab Welcome Center.


Masks are welcome, not required, per University policy

The tour route will travel through fields with uneven terrain. Farm cart transport (e.g. gators) can be available for those who request assistance.

Schedule of Events


Field Tour
11 :00 -11:15 Station 1. Welcome, overview of the program and biostimulant research on Shade-Trees
11:15 – 11:30 Station 2. Plant-based irrigation scheduling: pressure bomb and infra-red thermography
11:30 – 11:45 Station 3. ET-based irrigation scheduling and Flatheaded borer research
11:45 – 12:00 Station 4. Cover cropping and Heat-stress prevention
12:00 – 12:15 Station 5. Boxwood blight control
12:15 – 12:30 Station 6. LiDAR “smart” air-blast sprayer and drone demonstration

12:30 – 1:00 Station 1. Open chat with research team, refreshments and grilled sides.

Open House
1:00 – 2:00 Self guided tour. Researchers will be at each of the six stations to answer questions. Sprayer demos will take place at station 6 every 15 mins.