My project was designed to experiment with techniques to increase the viability of ground cherries as a fresh market and value-added crop, by improving harvesting conditions. A combination of grafting, pruning, and trellising were used to create a more upright habit to improve harvest time and labor intensity, while a net trough was employed to catch the fallen fruit and eliminate ground contact. Two plantings, one at Calliope Farm, and another at LESREC (Lower Eastern Shore Research and Education Center), consisting of a 100’ control row and a 100’ experimental row were used to compare time, yield and quality.
Totals are per 100 foot row (50 plants per row). Hours reported include bed preparation and pruning/infrastructure installation. The pruned and netted ground cherries yielded 40 – 74% of the control, and labor was 38 – 36% of the control at the home farm and research farm, respectively. Income above measured labor for the pruned ground cherries was 40% of the control at the home farm and 74% at the research farm.
The disparity of yields between the two locations were due, in part, to defoliation by three striped potato beetles at the Calliope Farm location. It is also felt that more efficiency could be made in the installation of the netting thus reducing labor even more for the pruned treatment. Pruned plants produced less overall, but fruit was larger, averaging 5/8”-3/4” from pruned plants versus ½”-5/8” from un-pruned plants. The quality of the fruit collected from the net trough was higher due to eliminating contact with the ground, especially following rain. Collecting fruit from the net trough was much easier and preferred, by myself, and all farmhands involved.
While the results are not entirely conclusive, we were able to establish that there is potential for improving the quality and the harvest time and labor of ground cherries by using pruning techniques and some infrastructure in the field. Though the grafting portion of the project was not very productive, we know now that it is possible to graft ground cherries (physalis pruinosa) to tomatillos (physalis ixocarpa), which I could find no record of having been tried before.
Results were shared at the University of Maryland Eastern Shore Small Farm Conference, November 7, 2015, and at a Specialty Crop Workshop at the Wye Research and Education Center, Queenstown, MD on December 8, 2015. Both events had approximately 50 attendees.
Calliope Farm is a small CSA and market garden on the Delmarva Peninsula of Maryland. We specialize in heirloom, open-pollinated, ethnic and exotic fruits and vegetables in order to expose our members and community to the wide variety of produce not commonly found in grocery stores, as well as to find varieties that respond well to low-input, organic methods of growing. We have found that ground cherries (physalis pruinosa), which were relatively unknown when we started bringing them to market seven years ago, are very popular with customers, but difficult to meet the demand for due to the labor intensiveness of harvest. Ground Cherries are, otherwise, prolific and easy to grow, and one planting will produce fruit for several months over the summer. In addition, they store well and have potential for use in many value added applications.
Our objectives in experimenting with field infrastructure, pruning and grafting of ground cherries are to:
- increase the speed of harvest
- reduce intensity of labor during harvest
- improve quality of fruit by eliminating ground contact
- improve food safety by eliminating ground contact
By pruning, staking and clipping the plants to string, we are attempting to create a more upright habit, so that a net trough can be attached below the fruit canopy. Fruit will then fall into the trough, rather than on the ground, and harvesters can scoop up fruit more quickly, and with less time bent over, or on hands and knees. A decrease in time and labor of harvest will, hopefully, increase the volume of fruit that can be brought to market, and improve the economics of ground cherries as a commercial crop.
On March 16, 2014, 1×288 tray of Cossack Pineapple Ground cherries was started from seed purchased from Southern Exposure Seed Exchange, using bottom heat to aid in germination. The smaller cells were used because of limited space on the heat mat. After germination, and once the plant had two true leaves, plants were upsized into 2.5” pots.
The third week of May, 2014, two 3’ wide x100’ long, raised beds were planted with Cossack Pineapple ground cherries at 2’ spacing using black landscape fabric as ground cover, with drip irrigation. One row was grown as a control, with no pruning or intervention. A second row was planted and had stakes driven every five feet, to support two plants between every set. Plants were pruned to a single or double leader two weeks after planting (6/8), and again, two weeks later (6/23), to remove any stems below growing below approx. 8”.The pruning created a more upright habit and allowed plants to be supported by using tomato clips to attach branches to twine. Prior to first harvest, the second week of July(7/13), crosspieces were attached to every other stake to make a “T” shape and a trough was created by cutting a 7’x100’ piece of insect netting lengthwise and attaching it underneath the plant canopy, using clothespins to clip the net to the bottom string, and bailing twine to attach the net to the crosspieces. The netting was used to catch the fruit, eliminating contact with the ground, and making them easier to harvest.
The experiment, using the same plant stock, timeline and materials, was replicated at the Lower Eastern Shore Research and Education Center (LESREC), in their 3 acre organic plot.
Data on yield, time spent harvesting, and fruit quality was collected twice weekly harvests from both locations.
Due to cool spring temperatures ground cherries were transplanted to the field two weeks later than planned, but plants grew vigorously once in the field. The process of pruning and setting up the support infrastructure for the experimental rows added about 8 hours of labor, initially, but saved significant time during harvest.
The planting at Calliope Farm suffered damage from three striped potato beetles. We were able to control them by hand picking early in the season, but they eventually grew in population, and about a third of the experimental (pruned/staked) row was defoliated. The replication planting at LESREC did not suffer any damage from pests, and ultimately produced higher yields, and continued to produce for a longer period.
The portion of the experiment dealing with grafting was not fulfilled as intended because the nursery who was commissioned to provide grafted plants had very poor germination, and the attempts they made at grafting a few of the plants failed. It was unclear why their grafts failed, but poor healing chamber design was suspected, so upon notification that they would be unable to complete the order I asked to re-allocate funds so that I could build my own healing chamber and attempt to do the grafting myself. I was able to successfully graft two plants, but the delay meant that they did not reach maturity in time to compare to the other treatments. However, I did confirm that it is possible to graft ground cherries to tomatillos, which had never been done before.
Because ground cherries produce three to four stems that emerge at ground level, pruning the plants to a single leader resulted in removing a large portion of the mass of the plant. Although the pruned plants matured at the same rate as un-pruned plants, the number of flowers, and subsequent fruit was less at the onset of fruiting. It took approximately one month for the experimental plants to reproduce growth higher up on the plant and for fruit yields to catch up. However, the pruned plants produced slightly larger fruit, averaging 5/8”-3/4”, versus ½”-5/8” berries from the un-pruned plants.
Yields and labor to plant and establish and prune were:
Calliope control planting: Total hours-20.2, Yield- 158.15 lbs
Calliope experimental planting: Total hours- 7.65 (38% of control), Yield- 63.62 lbs (40 % of control)
LESREC control planting: Total hours-37.06, Yield- 242.9 lbs
LESREC experimental planting: Total hours- 13.5 (36% of control), Yield- 178.75 (74% of control)
Ground Cherries were sold at market for $4/pint, equaling $14/lb. Rate of pay was $12 for farm labor. Profit from each 100 ft row, after subtracting cost of labor from income from sales were as follows:
Calliope control planting: $2214.10 (higher yields)
Calliope experimental planting: $890.96 (lower yields)
LESREC control planting: $3400.60 (higher yields)
LESREC experimental planting: $2502.50 (lower yields)
I was unable to fulfill the grafting portion of the experiment due to problems with the nursery that was commissioned to provide grafted plants. I was, however, able to graft a few plants myself, which indicates that the plants are compatible, but it was too late for the plants to reach maturity.
While the results are not entirely conclusive, we were able to establish that there is potential for improving the quality and the harvest time and labor of ground cherries by using pruning techniques and some infrastructure in the field.
We also know now that it is possible to graft ground cherries (physalis pruinosa) to tomatillos (physalis ixocarpa), which I could find no record of having been tried before.
Education & Outreach Activities and Participation Summary
Results of the experiment were presented at:
Small Farm Conference, University of Maryland Eastern Shore, Princess Anne, MD November 7, 2015
Specialty Crop Program, Wye Research and Education Center, Queenstown, MD, December 8, 2015.
Both events had an average of 50 attendees
There were both positive and negative results associated with the technique of pruning and training. Removing much of the lower portion of the plant decreased the number of flowers, and thus fruit, early in the season, and took approximately one month for the plant to fill out on top so that yields could catch up with the un-pruned plants. This occurred at the height of market season, which would represent a loss of income. However, yields did catch up and the fruit was slightly larger, and the quality of the fruit was greatly improved by avoiding contact with the ground. In addition, the net trough significantly improved the speed of harvest, and intensity of labor for harvesters. Myself, and all farmhands agreed that harvesting out of the net rough was preferable.
It’s possible that starting plants earlier in the nursery, so that plants are larger when transplanted to the field, could speed up earlier fruit yields.
If the intended use is for value added products, then the delay would matter less, and the pruning/staking/trough treatment would certainly be worthwhile.
The technique of pruning and staking, combined with the net trough, has potential to greatly improve the physical and economic viability of ground cherries as fruit crop. However, further experimentation is needed to address the negative outcome of delayed crop yields.