University of Pennsylvania ScholarlyCommons Internship Program Reports Education and Visitor Experience 2019 Evaluation of the Crabapple (Malus) Collection and Assessment of the Crabapple Slope Micah Christensen University of Pennsylvania Follow this and additional works at: https://repository.upenn.edu/morrisarboretum_internreports Part of the Horticulture Commons Recommended Citation Christensen, Micah, "Evaluation of the Crabapple (Malus) Collection and Assessment of the Crabapple Slope" (2019). Internship Program Reports. 40. https://repository.upenn.edu/morrisarboretum_internreports/40 An independent study project report by The Charles C. Holman Endowed Rose and Flower Garden Intern (2018-2019) This paper is posted at ScholarlyCommons. https://repository.upenn.edu/morrisarboretum_internreports/40 For more information, please contact [email protected]. Evaluation of the Crabapple (Malus) Collection and Assessment of the Crabapple Slope Abstract This project began in response to space on the slope for more crabapple trees and a need to evaluate the current crabapple collection. As such, this project examined the collection as a whole with special attention to the slope. The Morris Arboretum had 48 crabapple trees as of 2018. The vast majority were planted in two locations: the slope by the rose garden and on the farm between the community garden and the executive director’s residence. The initial examination of the collection showed only two native crabapple specimens (Malus coronaria) both with a provenance of Maryland. Propagation of a tree with more local provenance was done to improve and expand the Malus collection. The four parts to this project included development and implementation of evaluation criteria, soil testing of the slope, recommendations of crabapple cultivars to fill empty spaces on the slope, and propagation of a native crabapple (Malus coronaria) with local provenance Disciplines Horticulture Comments An independent study project report by The Charles C. Holman Endowed Rose and Flower Garden Intern (2018-2019) This report is available at ScholarlyCommons: https://repository.upenn.edu/morrisarboretum_internreports/40 TITLE: Evaluation of the Crabapple (Malus) Collection and Assessment of the Crabapple Slope AUTHOR: Micah Christensen The Charles C. Holman Endowed Rose and Flower Garden Intern DATE: March 6, 2019 ABSTRACT: This project began in response to space on the slope for more crabapple trees and a need to evaluate the current crabapple collection. As such, this project examined the collection as a whole with special attention to the slope. The Morris Arboretum had 48 crabapple trees as of 2018. The vast majority were planted in two locations: the slope by the rose garden and on the farm between the community garden and the executive director’s residence. The initial examination of the collection showed only two native crabapple specimens (Malus coronaria) both with a provenance of Maryland. Propagation of a tree with more local provenance was done to improve and expand the Malus collection. The four parts to this project included development and implementation of evaluation criteria, soil testing of the slope, recommendations of crabapple cultivars to fill empty spaces on the slope, and propagation of a native crabapple (Malus coronaria) with local provenance. 1 Evaluation of the Crabapple (Malus) Collection and Assessment of the Crabapple Slope TABLE OF CONTENTS ABSTRACT………………………………………………………………………………………1 BACKGROUND...……………………………………………………………………………….3 METHODS…………………………………………………………………………………….....3 Evaluation of the Collection……………………………………………………………..3 Propagation of Malus coronaria………………………………………………………...4 Crabapple Slope Soil Test……………………………………………………….………7 RESULTS and DISCUSSION…...……………………………………………………………...5 Evaluation of the Collection……………………………………………………………..5 Crabapple Slope Soil Test……………………………………………………………….7 Recommended Cultivars for the Crabapple Slope…………………………………….7 Propagation of Malus coronaria………………………………………………………...9 CONCLUSION and RECOMMENDATIONS……………..……………………………….....9 Recommendations for the Crabapple Slope…………………………………………..10 ACKNOWLEDGEMENTS……………………………………………………………………13 WORKS CITED…………………………………………………………………..……………14 APPENDIX…………………………………………………..…………………………….……15 Recommended Sources for Malus ‘Rambo’ Interpretive Signs……………………..15 Figures…………………………………………………………………………………...15 Tables……………………………………………………………………………………16 2 BACKGROUND Crabapples are in the genus Malus along with common culinary apples. The difference between crabapples and apples is simply size. Crabapple trees produce smaller fruit than apple trees. Generally, two inches is considered the cutoff between crabapples and apples (Hinkamp). The Morris Arboretum’s Malus collection included 48 trees in 2018 including: ‘Rambo’ (a culinary apple), many ornamental crabapples, some straight species crabapples, and two native wild collected Malus coronaria hybrids. The vast majority were planted in two locations: the slope by the rose garden and on the farm between the community garden and the executive director’s residence. An initial look at the collection to form the plans for this project showed a lack of native crabapples (Malus coronaria). Our only specimens were two very young Malus coronaria hybrids with a provenance of Beltsville, Maryland. Since Malus coronaria is native to southeastern Pennsylvania as well, this project included a wild collection from Willistown Township, Pennsylvania to improve and expand the Malus collection. Nearly all of the dwarf ornamental cultivars are growing on display for the public on the slope. When the slope was designed, cultivars noted for high disease resistance were selected; however, now it has become apparent that many of the cultivars are either less resistant in our area or the diseases have adapted significantly. This presented an opportunity to begin evaluating our collection. In addition, the wet weather throughout 2018 increased disease pressure making it clear which cultivars truly had high disease resistance—unfortunately this included only a few trees on the slope. The evaluation results were used to help inform new cultivar recommendations. In preparation for planting additional crabapples, this project included testing the soil on the crabapple slope. METHODS Evaluation of the Collection Evaluation criteria and methods had to be developed simultaneously with conducting the first evaluation of the collection since the crabapple trees were already losing their leaves due to disease when this project began in mid-August 2018. This led to differences in the data collected for the first evaluations compared to the final evaluations. For example, the first two evaluations recorded only the estimated percentage of disease covering an average leaf and the estimated percentage of canopy coverage or leaves still left on the tree. Since ornamental crabapples tend to be grown almost entirely for their spring flowers, and the slope is intended to showcase disease resistant cultivars, the crabapple collection was evaluated for categories related to flower quality, disease and pest resistance, and aesthetic fruit value. Early on this was recorded and evaluated as flower quality, fruit quality, fruit color, aesthetic foliage value, overall disease and pest resistance, and overall specimen health. The evaluation criteria were later streamlined to hopefully allow the whole collection to be evaluated in just a couple hours using a rubric with just four categories developed over the course of several evaluations. 3 Propagation of Malus coronaria Propagating a native wild crabapple with local provenance first required finding a nearby Malus coronaria tree. Tim Block, Ph.D., director of botany at Morris Arboretum, was consulted and knew of three potential locations. One location was along the Wissahickon Trail between Dekalb Pike (US 202) and North Wales Road—probably around GPS coordinates 40.186333, - 75.275833. Another location was along the edge of a field along the Perkiomen Creek just upstream from the East Greenville Water Authority facility at approximately 40.409038, - 75.521107. The third location was a parking lot for a soccer field by Willisbrook Preserve in Willistown Township. Due to unforeseen circumstances, Dr. Block was unable to come on the collection trip. To avoid possibly collecting from the wrong crabapple tree, the third location was chosen. The tree was unmistakable since it was growing by itself on the edge of a soccer field parking lot by Willisbrook Preserve (Photo 1). Plenty of crabapple fruits were collected along with two small branches for herbarium specimens. The collection form (Figure 1) is included in the APPENDIX. Other Malus species were noted in the area and likely pollinated the collected fruit, so the resulting trees from this propagation project have been accessioned as Malus coronaria hybrids. The branches were placed in a field press and later given to Dr. Block for mounting. Once collected, the fruits were placed in a plastic bag for partial fermentation. Initially, the fruits did not begin fermenting likely because they were stored outside in the cold. To speed up the process, the fruits were brought inside and some water was added to the bag. Once the fruits began softening, they were mushed inside the bag and fermented about a week longer. The seeds were removed and cleaned with direction from Shelley Dillard, Morris Arboretum propagator. Unfortunately, there Photo 1. Wild Malus Coronaria does not seem to be a good way to clean crabapple