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Phlox (diffusa)

USDA NRCS - Corvallis Plant Materials Center
3415 NE Granger Ave
Corvallis, Oregon 58413

Family Scientific Name: Polemoniaceae
Family Common Name: Phlox
Scientific Name: Phlox diffusa Benth.
Common Name: spreading phlox
Species Code: PHDI3
Ecotype: Crater Lake National Park, 7,000 ft elev on pumice flats and open gravelly slopes around Rim Village.
General Distribution: Western US and central plains on open, dry, gravelly or sandy soils, in openings and large clearings.
Propagation Goal: plants
Propagation Method: seed
ProductType: Container (plug)
Stock Type: 4
Time To Grow: 1 Years
Target Specifications: Healthy, branched crown foliage with healthy central tap root
Propagule Collection: Seeds are slow and tedious to collect from these low-growing plants; not present at all in some collection years and sparse in most; tend to wither if collected at less than full ripeness, single seed per flower.
Propagule Processing: No processing needed other than perhaps blowing away chaff / light, empty seeds
Pre-Planting Treatments: Germination significantly enhanced in our trials with 17 weeks cold moist pre-chill
Growing Area Preparation/
Annual Practices for Perennial Crops:
Seeds sown into standard "1040" flats with a fine, soil-less potting mix (Fisons' Sunshine #3 seedling starter); topped with a thin layer of fine vermiculite; watered-in and placed in polyethylene bags in a walk-in cooler at 34 - 36 F for 17 weeks.
Establishment Phase: Flats with stratified seeds placed in warm greenhouse (approx 60 nights / 70 to 85 F days) and lightly watered as needed until germination was complete, in about 45 days: approximately 50 % of seeds germinated with this treatment. Good air circulation and drainage is crucial; these seedlings are highly susceptible to damping-off and other fungal attacks. Seedlings remained in these flats for another 4 to 6 weeks until large enough to transplant. 1 gram of seed produced 36 healthy container plants for us in this trial.
Length of Establishment Phase: 12 weeks
Active Growth Phase: When large enough to handle for transplant, seedlings are placed in a light, fast-draining potting medium (Fisons' Sunshine Aggregate 4 Plus) in 4" deep pots and moved outdoors to a lightly shaded area (we placed ours at the outside northern edge of the shadehouse). Plants should be protected from overwatering and given plenty of room for air circulation. One light fertilization of Peters' started (9-45-15) given once after transplanting; excess fertilizer should be avoided on these slow-growing plants.
Length of Active Growth Phase: May to July
Hardening Phase: Plants can be allowed to become rather dry in August: pots should become quite light between waterings and then drained very quickly after watering.
Length of Hardening Phase: August - September
Harvesting, Storage and Shipping: Plants were shipped up to Crater Lake in late August via refrigerated van to a holding facility at the park; they can also be placed into a walk-in cooler with soil very lightly moistened for dormant storage over winter. Most important is for the plants not to be moved outside in early spring in Corvallis where they can become waterlogged and overwhelmed by foliar / fungal diseases.
Length of Storage: Seeds - not known; plants can be held over winter but may need transplanting to deeper containers in the following spring.
Other Comments: Although called "spreading", our experience with this phlox was that it produced only a single, very deep taproot. We did not find evidence of spontaneous root spreading in even the very large plants at the park; nor were we successful in producing significant numbers of transplants from stem cuttings.
References: Corvallis Plant Materials Center Technical Report: Plants for Woodland and Rangeland Reclamation and Erosion Control 1980 - 1997 (includes Annual Reports to Mount Rainier National Park from 1990 - 1996

Link, Ellen, ed. 1993 Native Plant Propagation Techniques for National Parks Interim Guide; Compiled by Rose Lake Plant Materials Center 7472 Stoll Road East Lansing, MI 48823

Kruckeberg, Aurthur R. 1982. Gardening With Native Plants of the Pacific Northwest: An Illustrated Guide. Seattle: Univ. of Washington Press.
USDA, NRCS. 2001. The PLANTS Database, Version 3.1 (http://plants.usda.gov). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.


Flessner, Theresa R; Trindle, Joan D.C.. 2003. Propagation protocol for production of Container (plug) Phlox diffusa Benth. plants 4; USDA NRCS - Corvallis Plant Materials Center Corvallis, Oregon. In: Native Plant Network. URL: http://NativePlantNetwork.org (accessed 2021/03/01). US Department of Agriculture, Forest Service, National Center for Reforestation, Nurseries, and Genetic Resources.

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