Season Extension of Hay-Mulched Potatoes Using High Tunnels

PROJECT BACKGROUND
Farm description: Certified organic produce on five acres – mostly hay-mulched fingerling potatoes sold fresh harvested at farmers’ markets.

Sustainable practices used before the grant included: Three-crop rotation with legume plow down. Hay mulch for fertility and weed control. Seven years (five on site).

PROJECT DESCRIPTION
Goals: Our goals were to
1) Grow potatoes under hay in a high tunnel beginning in winter for early spring fresh market
2) Grow potatoes in fall under hay in high tunnels and attempt to have the plants (with potatoes attached) go dormant for continuous fresh harvest through winter for the winter farmers’ markets.

Process: We completed the first half of our project as outlined in the project description in early 2007: “Using high tunnels, the project will grow fingerling potatoes under hay in fall for fresh harvest from the dormant plants during the winter months. One of the high tunnels would be ventilated in autumn, have drip tape applied, and receive an early fall planting and hay mulch of our best producing short-season variety of fingerling potatoes. Following the original four-season rationale of Eliot Coleman, our goal would be to have the plants reach maturity and set tubers before temperature and light levels fall below the threshold for growth. The high tunnel would then be closed and the now dormant plants covered with a geotextile to keep them from freezing.”

The High Tunnel for the first half of the project was ordered in July and delivered in late August. We erected it in September after preparing the site, and planted certified organic ‘Red Thumb’ seed potatoes while the soil temperature was still above 65 degrees F. We hayed over the seed potatoes as described above, leaving out the drip tape as we chose instead to add moisture with portable sprinklers as needed. (The soil and hay received several downpours before the high tunnel plastic was put on.) We installed soil thermometers and have kept weekly soil temperature readings and charted the changes in the seed potatoes.

We also harvested our comparison potatoes, the same fingerling variety from the same soil area, on the day we planted in the high tunnel. A few pounds of these potatoes were refrigerated at 41 degrees F to be available for comparison analysis of nutrients, etc.

We had expected the seed to sprout in October; it did not. The weather after planting turned unseasonably cold and the soil temperature, even under the thermal blanket of hay, quickly fell to 49 degrees F and stayed there throughout October and November. Outdoor soil temperatures in the adjacent plots went down to 28 degrees F over the same period. We put plastic on the high tunnel earlier than planned in the hope that higher daytime air temperatures (average daily high of 88 degrees F) inside the tunnel would heat the surface soil. The hay proved to be an excellent thermal blanket, keeping the soil at one inch depths at 49 degrees F. What we learned is that we are prone to under-estimating the difference in climate between the cloudy Great Lakes bioregion and our previous land in SE Ohio. The soil got colder much, much more quickly than we anticipated, albeit partly due to the unusual weather.

We repeated this portion of the experiment in fall of 2008 using young started plants that we transplanted from the field, first moving the mobile high tunnel to an adjacent plot and planting transplants (half on August 30 and half on September 30) to increase the possibility that we would have producing plants when we attempted to make the plants go dormant in late fall. Sixty-five percent of the plants survived transplanting, and most of these set tubers. However, even with row covers and a mean nightly low temperature in the hoop house of +/- 27 degrees F, all the plants died in the second week of November. This leads us to believe that potato plant mortality is probably tied to photoperiod. The seed that the plants grew from generally died as well, although a small number appear to have survived and may produce new plants in the spring.

We built our second hoop house in the early spring and planted seed potatoes under hay in March when soil temperatures in the hoop houses rose above 60 degrees F. We did not use the soil-warming mulch.

RESULTS
We tracked growth rates and periods for the early market season extension part of the project and they were slightly better even than summer growing. We recorded harvest dates and approximate yields and these as well were higher (25%) than the summer harvest from the previous year. We also noted that we did not need to spray Neem for Colorado potato beetle, which is almost always required at least once for the summer crops. The season extension for early harvest was successful and we will continue it as we are able, and plan to expand the use of high tunnels for this purpose.

PEOPLE
Dr. Matthew Kleinhenz, Extension Vegetable Crops Physiology and Production Specialist, Department of Horticulture and Crop Science with The Ohio State University, Ohio Agricultural Research and Development Center (OARDC) advised us on record keeping, etc.

Ohio Ecological Food & Farm Association (OEFFA) publicized our field day which was rained out. For more information on OEFFA see: http://www.oeffa.org/

DISCUSSION
We learned that we can beat the cloud cover with high tunnels for early season extension. I am not sure whether we have proved to ourselves that it is not possible to make the potato plants go dormant in winter – there may have been a number of factors involved in the sudden die-off – but to be certain we would have to do further research on photoperiod sensitivity under more controlled conditions than we can attain as farmers.

I would strongly suggest two things to other farmers growing for early market in the upper Midwest: High tunnels work, and mobile high tunnels are vulnerable to the wet conditions and high winds of winter. Both of our tunnels sustained heavy damage after the end of the project from high winds (just after soaking rains which had the effect of loosening the hold of the ground anchors.) I would recommend more numerous and much larger and longer ground anchors than supplied with most kits.

OUTREACH
We held a field day which was rained out – but we were able to distribute information.

EVALUATION
We could not have completed our research otherwise – time and money are premiums for entrepreneurial farmers.

We have had many opportunities to share our farming philosophy with others due to their notice of our project.

We are extending the season – extending our markets – and we are using soil building techniques under cover.

The program was transitioning to the new sponsoring location during our project, which made for more paperwork. Farmers and ranchers cannot devote the same amount of time to bookkeeping and red tape as can non-profits.

I would like to see renewed emphasis on small-scale equipment and production methods, and a focus on adopting small holder techniques from other countries.