Boechera (horizontalis)

Lee Riley Horticulturist USDA FS - Dorena Genetic Resource Center 34963 Shoreview Road Cottage Grove, Oregon 97424 541-915-7324 541-767-5709 (fax) lee.riley@usda.gov

---

Family Scientific Name:	Brassicaceae
Family Common Name:	Mustard
Scientific Name:	Boechera horizontalis
Common Synonym:	Arabis suffrutescens var. horizontalis
Common Name:	Crater Lake rockcress
Species Code:	ARSUH
Ecotype:	Crater Lake National Park, Oregon
General Distribution:	Boechera horizontalis is known from only four to six extant occurrences in Oregon, all but one or which are within Crater Lake National Park. It is listed as critically imperiled
Propagation Goal:	Plants
Propagation Method:	Seed
ProductType:	Container (plug)
Stock Type:	262 ml (16 in3) container
Time To Grow:	16 weeks
Target Specifications:	Stock Type: Container seedling Root System: Firm plug in container.
Pre-Planting Treatments:	Due to small seed size, the easiest method is to sow seed into trays filled with stabilized medium plugs (Q-plugs). Trays are sealed inside plastic bags and placed into refrigeration at 1 to 3 °C for 90 days. Trays are checked weekly and kept moist throughout the stratification period. If mold is evident, trays should be treated with 1% hydrogen peroxide.
Growing Area Preparation/ Annual Practices for Perennial Crops:	Greenhouse growing facility. Q-plugs are lightly covered with nursery grit. Seedlings are transplanted to target containers approximately 3 weeks following germination. Growing medium used is 40:20:20:20 peat:composted fir bark:perlite:pumice with Nutricote controlled release fertilizer (18N:6P2O5:8K2O with minors; 180-d release rate at 21C) at the rate of 1.5 gram Nutricote per 262 ml container.
Establishment Phase:	Germination is uniform and but somewhat slow. It is usually complete in 14 to 21 days. Following germination (while still in Q-plugs), plants are fertilized with soluble 12-2-14-6Ca-3Mg at 75 ppm for 1 week.
Length of Establishment Phase:	3 weeks
Active Growth Phase:	Both shoot and root development are somewhat slow, but plugs will be plantable in the first year. Soluble fertilizer (20-9-20 NPK, 20-18-18 NPK, or 17-5-24 NPK) at 100 to 150 ppm is applied weekly throughout the growing season.
Length of Active Growth Phase:	18 weeks
Hardening Phase:	No dry-down is done to induce dormancy. Seedlings are moved to an outdoor growing area in early September.
Length of Hardening Phase:	3 to 4 weeks
Harvesting, Storage and Shipping:	Harvest Date: Early October Storage Conditions: Seedlings are usually outplanted in fall. No storage except in outdoor growing area. Plants are well irrigated prior to shipping and shipped in containers.
Other Comments:	Perennial All known Oregon populations are small and only one is believed to have good viability. Human recreation (trampling by hikers) as well as impacts from logging on nearby lands are the major threats to this plant.
References:	[CPNH] Consortium of Pacific Northwest Herbaria. Boechera horizontalis. URL: http://www.pnwherbaria.org/m/datasets/vascular-plants/pages/brassicaceae/boechera-horizontalis.htm (accessed 23 Feb 2021). Dorena Genetic Resource Center Propagation Records, unpublished. [FNA] Flora of North America. 2007. Boechera horizontalis (Greene) Windham & Al-Shehbaz. Flora of North America Vol. 7: pp 360,361,384. URL: http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=250094583 (accessed 23 Feb 2021). [ITIS] Integrated Taxonomic Information System. Boechera horizontalis (Greene) Windham & Al-Shehbaz. URL: https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=823127&print_version=PRT&source=to_print#null (accessed 23 Feb 2021). NatureServe Explorer. Arabis suffrutescens var. horizontalis Crater Lake Rockcress. URL: https://explorer.natureserve.org/Taxon/ELEMENT_GLOBAL.2.159247/Arabis_suffrutescens_var_horizontalis (accessed 23 Feb 2021).

Citation:

Riley, Lee E.. 2021. Propagation protocol for production of Container (plug) Boechera horizontalis Plants 262 ml (16 in3) container; USDA FS - Dorena Genetic Resource Center Cottage Grove, Oregon. In: Native Plant Network. URL: https://NativePlantNetwork.org (accessed 2025/04/11). US Department of Agriculture, Forest Service, National Center for Reforestation, Nurseries, and Genetic Resources.