Monitoring for frost in the Mid-Atlantic

By John Lea-Cox, April 12, 2015

Spring has taken a while to come to the Mid-Atlantic region this year.  After an unusually cold February, March turned wet and grey.  But early April brought some warmth and finally the daffodils, forsythia, cherries and even a few early dandelions are now in full bloom.  Talking to my colleague Bob Rouse, he estimates we are between 5% and 10% bloom for strawberries in the southern parts of Maryland, while those a little farther north are perhaps 7-10 days behind.

For many, spring is a welcome relief; for our strawberry growers, it’s typically a time of anxiety because the last frost date in the Mid-Atlantic is between May 1st and 15th, which is a full month away.  So all eyes are on the weather forecasts, in anticipation of early mornings when they rise at 3 or 4 am to check temperatures in their fields, and if that critical 32.5°F is reached, then the overhead sprinklers get turned on to save those precious flower buds.

Radiation frost detectors installed to measure leaf and floral temperatures.

Radiation frost detectors installed to measure leaf and floral temperatures.

But this year, thanks to NSSI funding, a couple of Maryland growers have a little extra help with getting both flower and leaf temperature data delivered in real-time to their cellphones, from advanced radiation frost detectors (Apogee Instruments, Inc.) located right in their strawberry canopies.  Eight of these sensors (pictured left) are located in each quadrant of the field.  The floral thermistor is just visible as a black wire in the center of the picture; the leaf thermistor is at right.  The data from these sensors and the weather station on site is transmitted via wireless radio nodes (Decagon Devices, Inc.) to a radio base station and computer located in the barn at the farm.

The base station and Sensorweb software (Mayim, LLC) receive that data every 5 minutes, where it is accessible over the internet via a password-protected website for the farm.  As an example (see figure below), we can plot the average leaf (green) and flower (orange) temperature and compare that to the weather station air temperature (black line), and relate that to the photosynthetic radiation (blue line) during the day.  Note that air temperature reached 34.5°F early on the 12th April, but leaf and flower temperatures reached a minimum of only 39.6°F and 38.6°F respectively — a 4 to 5°F differential from the air temperature.

A graph of average leaf (green) and flower (orange) temperature, weather station air temperature (black line), and photosynthetic radiation (blue line).

A graph of average leaf (green) and flower (orange) temperature, weather station air temperature (black line), and photosynthetic radiation (blue line).

Perhaps more useful to the growers is that they can set various threshold temperature alerts in the software that will automatically text their cellphone when that temperature is reached.  For example, a grower can get a text when the temperature from a flower sensor located in a frost pocket reaches 38°F.  We’re hopeful that this information will help them rest a little easier this spring!

But that’s only part of the story.  The real reason we are using sensor networks is to use sensor-controlled irrigation in the fields – not only to save water (which is critical for our California growers), but also to keep nutrients in the root zone for as long as possible and reduce leaching.  This is critical for growers in Florida as well as the Chesapeake Bay.   We are doing that with a combination of soil moisture and electrical conductivity sensors, again providing that information to our growers in real-time to help them make more informed irrigation decisions.

We’ll keep you posted on those results, as we progress through spring and early summer.  You can also learn more about our project objectives and our grower partners from our website at

NSSI E-Book Released!

We are proud to announce the release of our e-book, Moving the Needle: Accomplishments of the National Strawberry Sustainability Initiative 2013 – 2014. This interactive e-book is a downloadable PDF that provides access to the 70+ resources (tools, videos, and publications) developed during Phase I of the NSSI Grants Program. This summary of accomplishments includes specific outcomes and impacts from each of the 20 projects. Jump to the appendix to access a complete list of hyperlinks for strawberry videos and resources. You can find the download link on our website,

two page preview

We have also created a full version of the e-book that contains embedded videos for each of the projects. This version is too large for download, but if you are interested in obtaining a copy, please contact us at sberries(at)

Cold Climate Strawberry Farming E-Book

This blog post highlights the work of the NSSI project titled “Development of a Comprehensive, Engaging E-Learning Tool for Strawberry Farmers” led by Dr. Emily Hoover of the University of Minnesota

By Echo Martin, University of Minnesota

Where do farmers go to discover new techniques and information? In the past it was to conferences or other farmers, but more commonly today the first place people turn to is the internet. Many great outreach resources are available online, but sometimes navigation can be difficult and some articles are up to date, while others are a decade old. Additionally, the information can be difficult to access in the field if it’s not on a mobile website or isn’t downloadable.

Phase I Final Reports Due Next Week

Phase I is nearing completion and project leaders are reminded that final reports are due next week on August 15th. Thank you for your hard work, and we look forward to reading about what you discovered in the push for sustainable strawberries.

Hydroponic Strawberry YouTube Channel

Commercial growers now have free access to hydroponic strawberry start-up advice on YouTube, thanks to NSSI researchers. This collaboration between projects at the University of Arkansas and the University of Arizona demonstrates the mechanisms implemented on hydroponic and soilless setups at both locations.

The goal of this project was to provide a free portal to teach commercial strawberry growers how to build, manage, and use hydroponic systems in the production of strawberries. By using soilless and hydroponic systems to produce strawberries, growers are able to manage water and fertilizer more effectively. Additionally, many issues that are common in field-grown operations (soil sterilization/disinfestation, weed control, runoff) are eliminated.

You can view the Introduction video here.

The videos are each about 3-6.5 minutes in length and cover topics such as cultivar selection, fertilizer distribution equipment, pest and disease management, and harvesting.

Want to learn more about hydroponic strawberries? Then watch the rest of the videos at the project’s YouTube channel:

Walmart Foundation’s $1.05 Million Donation Fuels Second Phase of Strawberry Initiative

By Mary Hightower, U of A System Division of Agriculture

July 17, 2014

FAYETTEVILLE, Ark. – Ripening in mid-winter. Taking root in old cotton acres. Growing organic in conventional farms. America’s favorite berry is finding itself in places it’s never been before thanks to research, creativity and a donation from the world’s largest retailer.

Each of these new directions was grown from a $3 million donation from the Walmart Foundation to the University of Arkansas System Division of Agriculture’s Center for Rural and Agricultural Sustainability, known as CARS. Last year’s donation gave birth to the National Strawberry Sustainability Initiative and would fuel 20 research projects in 13 states.

All of the innovations have one aim: to provide U.S. consumers with the freshest berries raised in the most sustainable way possible everywhere they’re grown, from small family farms to cooperatives. It’s no small target either. Strawberry production was valued at $2.4 billion in 2012, according to the USDA’s Economic Research Service. And USDA says they are the fifth favorite fruit among American consumers, prized for its sweet taste and good-for-you versatility in the kitchen.

“At Walmart we support the issues our customers and communities care about most –sustainability being one of them,” said Dorn Wenninger, Vice President of Produce and Floral, Walmart. “We’re excited to help the National Strawberry Sustainability Initiative enter Phase II where we’ll see innovation at work in the fields. As a result, we’ll have a better understanding of how to sustainably increase production and supply of one of our nation’s favorite fruits.”