2018 ASHS Annual Conference

The sale and planting of many Eurasian honeysuckles (Lonicera spp.) is largely discouraged within the horticulture industry of North America. Increasingly, states legislatures have sought to ban the sale of Lonicera and other nonnative, invasive plants from commerce. A notable exception is the recent introduction of various cultivars of honeyberry (Lonicera caerulea) of Eurasian origin into the North American market, where they may have value in landscaping and as a berry crop. Because honeyberry is already listed as a serious invader of boreal forests in Norway, we decided to assess the potential competitive ability of honeyberry in a North American context by comparing the growth of rooted cuttings in containers to the growth of both mountain fly honeysuckle (Lonicera caerulea var. villosa), a diminutive, ecologically rare conspecific native to North America, and Tatarian honeysuckle (Lonicera tatarica), an invasive congener. We grew cuttings of each in a peat-based substrate in #1 nursery containers, which were top-dressed at the start of the experiment with Osmocote Pro 17-5-11 4-month controlled-release fertilizer (CRF) at rates of 5, 10, 15, 20, and 25 grams of fertilizer per container. After four months, Tatarian honeysuckle produced the greatest dry biomass, with nearly five times the shoot dry weight (SDW) and root dry weight (RDW) of honeyberry, which in turn produced about twice the SDW of mountain fly honeysuckle. SDW of Tatarian honeysuckle exhibited a strong response to increased substrate fertility, producing more than twice the SDW when fertilized with 20 grams than with 5 grams of CRF. Neither mountain fly honeysuckle nor honeyberry displayed a significant SDW response to increasing CRF application rates, indicating they may be less able than Tatarian honeysuckle to quickly respond to flushes of substrate fertility. Although honeyberry produced only one-fourth the RDW of Tatarian honeysuckle, it produced between two to three times the RDW of mountain fly honeysuckle. Finally, honeyberry rivalled Tatarian honeysuckle in cumulative length of primary stems, far exceeding that of its conspecific, and oriented more toward rapid vertical growth. Despite the classification of mountain fly honeysuckle and honeyberry within a single circumboreal species complex, honeyberry produced several measures of growth that were at least double those of mountain fly honeysuckle, a finding that suggests the two taxa may not be ecologically equivalent. We recommend further comparative studies between honeyberry and its native and invasive congeners in North America, to clarify the relative risks and benefits of its cultivation.