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Oenothera (caespitosa)

Tara Luna
USDI NPS - Glacier National Park
West Glacier, Montana 59936
(406) 888-7835

Family Scientific Name: Onagraceae
Family Common Name: Evening Primrose family
Scientific Name: Oenothera caespitosa Nutt.
Common Name: Rock evening primrose
Species Code: OENCAE
Ecotype: Open slopes, Two Medicine, Glacier National Park, Glacier Co., MT.
General Distribution: O. caespitosa is widespread east of the Cascades to the Great Plains throughout the West. It occurs on roadcuts and shoulders, talus slopes, dry hills to open Ponderosa pine forests.
Propagation Goal: plants
Propagation Method: seed
ProductType: Container (plug)
Stock Type: 116 ml conetainers
Time To Grow: 8 Months
Target Specifications: Stock Type: Container seedling<br> Height: 3 cm, 10 true leaves<br> Caliper: n/a<br> Root System: firm plug in conetainer.
Propagule Collection: Seeds are hand collected in late August when capsules turn dark brown and woody. Seeds are black at maturity. Capsules are collected using pruning shears and are stored in paper bags prior to cleaning.
Propagule Processing: Seeds are cleaned by breaking the tough, woody capsules open with pliers and seeds are hand screened.
Seeds/Kg: 2,000,000/kg
Seed longevity is unknown.
Seed dormancy is classified as physiological dormancy.
% Purity: 100%
% Germination: 60%
Pre-Planting Treatments: 5 month outdoor cold moist stratification.
Growing Area Preparation/
Annual Practices for Perennial Crops:
Outdoor nursery growing facility.
Sowing Method: Direct Seeding. Seeds are covered with media.
Growing media used is 6:1:1 milled spaghnum peat, perlite, and vermiculite with Osmocote controlled release fertilizer (13N:13P2O5:13K2O; 8 to 9 month release rate at 21C) and Micromax fertilizer (12%S, 0.1%B, 0.5%Cu, 12%Fe, 2.5%Mn, 0.05%Mo, 1%Zn) at the rate of 1 gram of Osmocote and 0.20 gram of Micromax per conetainer.

Conetainers are filled and sown in late fall and irrigated thoroughly prior to winter stratification.
Seedlings germinate in spring under fluctuating outdoor temperatures and are grown under full sun exposure.
Seedlings are irrigated with Rainbird automatic irrigation system in early morning until containers are thoroughly leached.
Average growing season of nursery is from late April after snowmelt until October 15th.
Establishment Phase: Media is kept slightly moist during germination.
Initial germination appeared uniform and occurred following several days of temperatures at 21C or above during the day.
Length of Establishment Phase: 4 weeks
Active Growth Phase: Root and shoot development occurs rapidly following germination. 2 to 4 true leaves were evident 2 weeks after germination. Plants were fertilized with 13-13-13 liquid NPK at 100 ppm during the growing season. Plants had 10 to 12 true leaves and were root tight 8 weeks after germination. Plants are biennial and will not flower until the second year.
Length of Active Growth Phase: 12 weeks
Hardening Phase: Plants are fertilized with 10-20-20 liquid NPK at 200 ppm during August and September. Irrigation is gradually reduced in September and October. Plants were given one final irrigation prior to winterization.
Length of Hardening Phase: 8 weeks
Harvesting, Storage and Shipping: Total Time To Harvest: 8 months

Harvest Date: Late July
Storage Conditions: Overwinter in outdoor nursery under insulating foam cover and snow.
Length of Storage: 5 months
Other Comments: O. caespitosa is a tap rooted biennial which frequently appears in road shoulders after disturbance.
There are 4 botanical varieties: marginata, psammophila, purpurea, and montana.
References: Flora of the Pacific Northwest, Hitchcock and Cronquist, 7th edition, University of Washington Press, 1973.
Seeding Rate Statistics for Native and Introduced Species, Hassell, Wendel, U.S.D.I. and U.S.D.A., April 1996.
Seeds: Ecology, Biogeography, and Evolution of Dormancy and Germination, Baskin and Baskin, Academic Press, 1998.
Seed Germination Theory and Practice, Deno, Norman, Penn State University, 1993.


Luna, Tara; Evans, Jeff; Wick, Dale. 2004. Propagation protocol for production of Container (plug) Oenothera caespitosa Nutt. plants 116 ml conetainers; USDI NPS - Glacier National Park West Glacier, Montana. In: Native Plant Network. URL: http://NativePlantNetwork.org (accessed 2020/08/05). US Department of Agriculture, Forest Service, National Center for Reforestation, Nurseries, and Genetic Resources.

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