Author: Kate Fessler, Graduate student, Applied Plant Sciences
Day neutral strawberries introduce new opportunities for Minnesota specialty crop growers. Researchers at UMN are collaborating with Minnesota farmers to make this high value crop more accessible, by growing them on tabletop gutter systems.
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| Photo: UMN researchers are testing two day-neutral varieties on two different growing media in a tabletop strawberry study. |
A research refresher
As this summer’s horticultural production season hits its stride, it’s a great moment to highlight some of the new research developments happening on the St. Paul campus.
Strawberry production across the country has begun moving toward the use of day-neutral varieties. While the June-bearing strawberry season typically lasts from mid-June to early-July, these day-neutral types can produce from July well into October, depending on growing conditions.
Due to this lengthened production window, there are some concerns about pests, diseases, and increased labor needs. To address some of those issues and try to make this specialty crop as accessible as possible, the University of Minnesota has received a grant from the Minnesota Department of Agriculture to test the efficacy of a new day-neutral tabletop production system in Minnesota.
In this system, the plants are grown in elevated plastic troughs with their roots anchored in soilless media. They are watered and fed through a drip irrigation system that provides a precisely calibrated fertilizer solution to meet all of the plants’ nutritional requirements. More information about the specifics of this set up and the variables in the research project can be found here.
Starting a new season
Although our pilot season last year experienced its fair share of Covid-19 related delays, there was a lot to learn from the work that we accomplished last year. The overall goals of the project are to test whether this system is feasible for Minnesota growers, assess the overall yield of several cultivars grown in this system, and determine whether harvest is more efficient when using this elevated system.
The 2021 timeline for this project began in April when the plastic troughs came out of winter storage for decontamination, which ensures that any disease or pest presence from the last season is eradicated. New soilless media was then rehydrated and placed into the troughs to settle before planting occurred. We were able to plant at the very beginning of May, which let the plants get established on time for a July harvest.
New challenges and new benefits
For the first week after planting, our bare rooted transplants were watered with plain tap water while they broke dormancy. For the next three weeks we irrigated and fertilized simultaneously (fertigated) and removed flower trusses to support vegetative growth rather than fruit production. Although the plants are growing vigorously, they did experience some stress from the extreme weather conditions of the past month.
Our first unanticipated issue was wind damage. This is not a common problem for strawberry plants in the Upper Midwest as they are usually so low-lying. However, the elevated nature of this production system exposes them to more agitation from the strong westerly winds that blow across the St. Paul agricultural research plots. This damage manifests as dark green (almost black!) bruises on the petioles and undersides of the leaves, sometimes extending onto the top surfaces as well. This rubs off the protective cuticle of the leaves, so these bruises become desiccated and turn brown. Sometimes the wind can even break the petioles entirely!
In order to solve this problem, we erected a windscreen using simple materials: t-posts, scrap shade cloth, and zip ties. Many other types of cloth/fabric could also be used, such as row covers or landscape fabric. The screen has already gone a long way toward reducing the wind damage without negatively affecting the air circulation around the system that helps keep the plants disease-free.
The second unanticipated challenge of this season was the June heatwave that scorched so many crops across the state. Once again, the plants’ elevation makes it more difficult for them to regulate heat, particularly as they are planted in black plastic containers. There is some scientific literature that suggests high temperatures in the root zone of day-neutral varieties can cause issues with yield. With that in mind, we’ve begun collecting our own data on root zone temperature to see whether the heat wave negatively affects our production this season.
While there have been some issues with malformation of the juvenile leaves and flowers that were emerging during the heatwave, all of the growth that has come in recently looks healthy and uniform. There has been lots of pollinator activity in the troughs and only minor damage from pests such as leafhoppers and caterpillars. The warm, dry conditions and extra air flow around the system also mean that there is virtually no evidence of disease or fungal infections at this stage.
We have also been keeping a close watch for any evidence of nutritional issues with the plants. Strawberries grow best at a soil or media pH of 5.5-6.5. Since the city water in St. Paul runs at a balanced pH of 7 and our fertilizer solution clocks in at a pH of 2-3, there haven’t been any signs of nutritional deficiency so far. At our field site in Morris, the water pH is higher; but they have had a lot of success with adding sulphuric acid to their fertilizer solution to bring down their pH.. Researchers at both sites have also routinely flushed the systems with plain tap water to keep salts from building up and causing issues with the plants’ water uptake. Consistently measuring pH and salinity is an important part of taking care of this system, but thankfully it hasn’t been a difficult aspect to track or troubleshoot so far!
Looking ahead to harvest
The first berries are just starting to come ripe, and many more are on the way. There may be a slightly higher incidence of misshapen fruits from the flowers that were damaged by the extreme heat when they were forming, but most berries so far are attractively uniform in size, shape, and color.
While I’ve only eaten a few so far, the flavor has been outstanding! Once we start bringing in larger numbers, we’ll analyze their juice for sugars and acidity to get a more objective marker of flavor quality.
I look forward to hearing from our grower-cooperators and the other great farmers across the state who are trying out tabletop growing for the first time this season!
There will be more updates about this project as we progress through the summer and early fall, and UMN Extension and UW-Madison Extension will be offering a webinar with further information on Thursday, October 21st at 1pm CST, entitled “Building a tabletop day neutral strawberry system”. We’re excited to see you there!
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