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Kalmia (latifolia)

John M. Englert
USDA NRCS - Norman A. Berg National Plant Materials Center
Bldg. 509, BARC - East, E. Beaver Dam Road
Beltsville, Maryland 20705
(301) 504-8175
(301) 504-8741 (fax)

Family Scientific Name: Ericaceae
Family Common Name: Heath Family
Scientific Name: Kalmia latifolia
Common Name: Mountain laurel
Species Code: KALLAT
Ecotype: Great Smoky Mountains National Park, Cumberland Gap National Historical Park, National Capital Parks-East, Shenandoah National Park, George Washington Memorial Parkway
General Distribution: New Brunswick to Ontario and southern Indiana, south to Florida and Louisiana on coastal plain and in mountains. Found in acid soils, mostly rocky or sandy.
Propagation Goal: plants
Propagation Method: seed
ProductType: Container (plug)
Time To Grow: 0
Target Specifications: Stock Type: Container shrub. Height: Depends on size of container. From 8" to 18". Root System: Fine fibrous roots grow in a defined clump. Roots may not extend to bottom of deeper pots. If roots form a mat on exterior surface, slice or tease root ball prior to planting.
Propagule Collection: Collected in Cumberland Gap National Historical Park at 1)Pinnacles; 2)near top of Chadwell Gap and 3)Tri-State Trail by J. Copeland in 1991 and 1992; by J. Englert in 1996.
Propagule Processing: Seed Processing: Hand-cleaned. Mature capsules are collected in the park in October, air dried, and stems are removed. Dried capsules are crushed and sieved through screen #13 to separate chaff from seeds.
Seeds/Kg: Uncounted. Seed is very small, at millions per Kg.
Germination: Untested. We can expect 0.05 to 0.1 gram of seed to produce hundreds of seedlings. Seed needs to be spread thinly over media to prevent crowding.
Purity: Unknown.
Pre-Planting Treatments: Seed Treatments: Because of small size, .05 to .1 gram of seed is mixed with between 4 and 8 grams of talc and sifted over the surface of media to produce about 400-500 seedlings.
Growing Area Preparation/
Annual Practices for Perennial Crops:
Propagation Environment: Production of Kalmia in the greenhouse has been problematic in the past for several reasons. 1. The seedlings are extremely tiny and slow growing. 2. Low winter light (in spite of extended day lighting) will stop the growth of many Kalmia and Rhododendron seedlings from January - mid March. 3. Lower temperatures, and over-saturation can result in deterioration of the peat-based media causing ammonia toxicity, algae, moss, liverwort and fungal growth, fungus gnat infestations, excessive drops in pH and subsequent nutrient deficiencies or toxicity. Growing seedlings through the two-leaf stage has been difficult, even with bottom heat and watering, and high intensity lighting. We have had about a 20%-30% survival rate. Luckily, a tremendous number of seeds germinated.

We tried starting seeds in the greenhouse in March when natural light and greenhouse temperatures are higher, but have had low germination because media is prone to drying or over-heating, even under shading, and seedlings have suffered from leaf scorch.
Seedlings that survived March plantings put on only 1/2" growth the first year.

We are now (March, 2001) attempting to grow small-seeded ericaceous plants in a propagation room rather than in the greenhouse, under fluorescent lighting, with hand-misting, periodic bottom watering and regulated day/night temperaturesto avoid the climate extremes of the greenhouse. A huge number of seedlings can be germinated in a very small space with less inputs and better controls this way.

Seed Propagation Method: Seeds are surface sown by hand over fine media.

Container Type and Volume: Seed is sown into 4x4 trays which are placed in solid bottom 10 x 20 tray (to allow bottom watering.) Seedlings are pricked off and spaced in 4 x 4 trays again, then transplanted to 2" pots, quarts, 1/2 gallons and 1 gallon. We have not transplanted this crop to larger containers yet.

Growing Media: Germinating mix: 4:2:1 mix of screened horticultural peat, sand and perlite. (Too much perlite will float to surface and obscure the tiny germinating seedlings.)

Recommended pH of media is around 5.0. We have added dolomitic lime at about 40 grams per cubic foot mix to prevent excessive drops in pH. We have not added slow release fertilizer or micronutrients because of problems with toxicity should pH drop excessively. Seedlings grow slowly and may remain in the same media for months. Because media deteriorates over time, we have found that periodic careful transplanting of tiny seedling clumps to new media appears to rejuvenate the seedlings.

Transplant mix for seedlings: In one crop, seedlings that were transplanted to a peat:sand mix in 2.5" pots had small unthrifty tops (1-2") 9 months later, but developed proportionately huge matted fibrous root systems that filled the pot. Plants from the same crop transplanted to Pro-mix BX with slow release Nutricote developed 4-8" healthy tops within 8-9 months but had tiny root balls that barely anchored the plant in the top inch of media. We currently use a transplant mix for larger seedlings of 1:1 Sunshine #1 to peat.
Transplant mix for quarts and up: 1:1:1 mix of Sunshine #1:peat:pinebark with supplemental soluble fertilizer for acid-loving plants.
Establishment Phase: Sowing Date: Best results for first season establishment and growth were obtained by sowing seed in November and nursing the seedlings through the slow-growth phase which occurred from germination until March (about 3-1/2 months).

% Emergence and Date: Seeds sown November 20, 1997 germinated well in about 3 weeks. A fraction of a gram of seed will produce many seedlings, too numerous and small to count. (Estimated over 700).

Sowing/Planting Technique: 0.1 gram or less of seed is thoroughly mixed with 4 to 8 grams of talc and sprinkled over the surface of finely screened horticultural peat:sand:perlite mix in trays which have been bottom watered and sprayed with a fungicide. Seeds will remain on the surface of the media if it is very lightly compressed prior to sowing. Trays are set in solid-bottomed carrying trays (to allow bottom watering), on heating pads to keep media at about 72 degrees, and given continuous (24 hour) fluorescent lighting (8-12" above trays) until germination has occurred in about 3 weeks. Surface of media must not dry out, crust over or become too hot or too cold during the germination period.

Plastic covers on trays will help keep humidity high but shading from direct sunlight is necessary to prevent media from drying out or reaching excessive temperatures.

Establishment Phase: High intensity lights set to give 14-16 hour days. Seedlings sown in November were still too small to transplant in mid-February. Most mortality occurs during this slow-growth, 2-leaf period when seedlings can become necrotic and die from too much water, deteriorating media, too low/high media temperature, fungus and insects. By mid March, however, seedlings had put on enough growth to be transplanted to 2.5" pots.
Active Growth Phase: Rapid Growth Phase: Kalmia does not appear to have a rapid growth phase. The only batch of Kalmia that reached 1/2 gallon size within a year of sowing was started in November and transplanted to Pro mix. Although tops were large, root masses were very small and took 6 months to fill the pots. Seedlings that were moved from the greenhouse outdoors during the summer to a shaded location grew the best. Once established, we have had few problems with Kalmia mortality if the media is changed seasonally. Problems occur if plants stay in one batch of peat-enriched media too long. During the summer they are held in our shade house with overhead irrigation or in shaded wetland cells with bottom watering.
Hardening Phase: Hardening Phase: Kalmia appears to need a period of winter chilling to sustain new spring growth. Plants overwintered in the greenhouse did not flush in spring like plants over-wintered in a cooler.
Harvesting, Storage and Shipping: Total Time to Harvest: Depends on container size of finished plant. Our best crop produced 1/2 gallon and gallon-sized plants in 1.5 years. The average seems to be 3 years to gallon size.

Storage Conditions: Kalmia in smaller containers are overwintered in cold storage at 40§F. During winter, 2001, 1/2 gallon and gallon sized plants were overwintered under microfoam outdoors.

Seed storage: Kalmia seed remains viable under cool dry storage for years (15-20). Stored at National Plant Materials Center in a seed cooler at 40§F and 35% relative humidity.

Seed dormancy: None indicated.
Length of Storage: <b>Storage Duration:</b> November - late March.
References: Woody Plants of Maryland, Brown and Brown, Port City Press, Inc., 1992.

Manual of Vascular Plants, Gleason and Cronquist, D. Van Nostrand Co., 1963.

Richard A. Jaynes. Kalmia, Mountain Laurel and Related Species. Timber Press, Portland Oregon. 1997.


Davis, Kathy M.; Kujawski, Jennifer. 2001. Propagation protocol for production of Container (plug) Kalmia latifolia plants USDA NRCS - Norman A. Berg National Plant Materials Center Beltsville, Maryland. In: Native Plant Network. URL: http://NativePlantNetwork.org (accessed 2021/09/19). US Department of Agriculture, Forest Service, National Center for Reforestation, Nurseries, and Genetic Resources.

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