Propagation techniques - Various
(This amazing list originally compiled by Tammy Romero - giving credit where credit is due!)
RESOURCES FOR SEED STORING AND GERMINATION
Botanic Gardens Conservation International
Seed Conservation Resources
http://www.bgci.org/plant-conservation/seedhub/
Proper Seed Storage and Seed Storage-Life
Botanyca Seeds Shop
http://botanicallyinclined.org/germination-page/
Native Plant Network Propagation Protocol Database
http://npn.rngr.net/propagation/protocols
Seed Germination Theory and Practice, Second Edition
by Norman C. Deno
http://naldc.nal.usda.gov/download/41278/PDF
First Supplement
http://naldc.nal.usda.gov/download/41279/PDF
Second Supplement
http://naldc.nal.usda.gov/download/41277/PDF
Woody Plant Seed Manual
USDA FS Agriculture Handbook 727, April 2008
by Franklin T. Bonner
(if the link opens to the home page for the National Seed Laboratory, click on the 'Woody Seed Manual' link in the left Nav Bar)
http://www.nsl.fs.fed.us/nsl_wpsm.html
Woody Plant Seed Manual
USDA FS Miscellaneous Publication No. 654
Silvics of North America
Volume 1 - Conifers
http://www.srs.fs.usda.gov/pubs/misc/ag_654_vol1.pdf
Volume 2- Hardwoods
http://www.srs.fs.usda.gov/pubs/misc/ag_654_vol2.pdf
A guide to forest seed handling
with special reference to the tropics
Published by the Food and Agriculture Organization of the United Nations
compiled by R.L. Willan
First printing 1985
Reprinted 1987
http://www.fao.org/docrep/006/ad232e/AD232E00.htm#TOC
Ontario Rock Garden and Hardy Plant Society
Germination Guide
http://www.onrockgarden.com/germination-guide/plants
Missouri Botanical Garden
'Native Seed Propagation Methods' Manual
Life Expectancy of Garden Seeds
http://thegardengeeks.net/garden-articles/gardening-how-tos/255-life-expectancy-of-seeds
Prairie Moon Nursery
Gives seed stratification and germination requirements for plants that they sell - mostly native American plants:
https://www.prairiemoon.com/home.php
Plants for a Future
Database of plants with edibility information, gives propagation instructions
Success With Seeds Website
-Flower Seeds
http://www.successwithseed.org/flower-seed
-Edible Seeds
http://www.successwithseed.org/flower-seed
Sheffield's Seed Company
A nursery selling seeds of trees, shrubs, flowers, etc. With info on seed germination.
White River Source
Seed and seedling nursery - has germination information on seeds they sell.
http://www.whiteriversource.com
Seed Saving Supplies
http://blog.seedsavers.org/blog/top-10-seed-saving-supplies
Seed Savers Exchange Seed-Saving Webinars
-Legumes
Our Garden Gang Seed Germination Database
http://ourgardengang.tripod.com/seed_germinationdb.htm
Our Garden Gang Guide to Saving Seeds
http://www.ourgardengang.com/SavingSeeds.htm
Backyard Gardener Seed Germination Database
http://www.backyardgardener.com/tm.html
Seedaholic Seed Database
Seed germination and plant cultivation information - Actually a seed catalogue. Select the plant from the database, then click on the 'Detail and Pictures' link for a plethora of information about the plant, including botanical information, sowing and germinating seeds, growing the plants and ways to use the plants.
Hardy Seeds Germination Database
http://www.hardyplants.com/A.htm
List of Heirloom Seed Suppliers
http://www.off-grid.info/food-independence/heirloom-seed-suppliers.html
Garden Gnome's Adventures Seed Germination List
http://www.freewebs.com/garden-gnomes-adventures/sowinggerminationlist.htm
Vegetable Seed Saving Handbook
http://howtosaveseeds.com/seedsavingdetails.php
-How to Breed Your Own Varieties
http://howtosaveseeds.com/breeding.php
Seed Alliance Seed Saving Info for Vegie Crops
http://www.seedalliance.org/uploads/publications/Seed_Saving_Guide.pdf
Seed Savers exchange
-Seed Saving Resources
http://www.seedsavers.org/Education/Seed-Saving-Resources/
The Seed Site
A plethora of pages on the subject of seeds - collecting, storing, sowing, germinating, etc. Plus, at the bottom of some pages, there are links to other useful websites! The Database has photos of the seeds and seedlings.
http://theseedsite.co.uk/index.html
Seed Saving and Seed Savers' Resources
http://homepage.tinet.ie/~merlyn/seedsaving.html
Storing Vegetable and Flower Seeds
(Tells how many seeds per gram/ounce,and how long the seeds can be stored)
http://www.ext.colostate.edu/pubs/garden/07221.html
Rob's plants - seed starting details by botanical name
http://www.robsplants.com/seed/germination.php
Tom Clothiers Garden walk & talk
- loads of advice on growing from seed - germination data, techniques and other useful info
Plants DB
Mostly herbaceous flowering plants and vines. Has photos of the seeds.
http://www.plantsdb.gr/en/propagation/seeds/328-seed-germination-database
RESOURCES FOR GENERAL PROPAGATION INFORMATION - WEBSITES
Links checked and updated 12/27/2017
GENERAL PROPAGATION REFERENCE RESOURCES
Greenhouse Product News, August 2005 'Rooting Hormones' by Christopher Cervenyand James Gibson
http://gpnmag.com/wp-content/uploads/GROWE.pdf
Kwantlen Polytechnic UniversitySchool of Horticulture Plant Database
Grow'em Plant Propagation Database
http://www.grow.ars-informatica.ca/index.php
Native Plant Network Propagation Protocol Database
http://www.nativeplantnetwork.org/Network/
California Native Plant Society Santa Cruz County Chapter
'Propagation by Cuttings'
http://www.cruzcnps.org/PropagationHandbook-SantaCruzCountyCNPS.pdf
Master Gardener Plant Propagation Table
Common Garden Plants
http://www.mgofmc.org/docs/propperennials.pdf
Perry's Perennial Pages
Dr. Leonard Perry's Web pages for on-line perennial and related horticultural information
http://pss.uvm.edu/ppp/proptabA.htm
PROPAGATION BY PLANT TYPE
SUCCULENTS
http://www.succulents.us/dormancy.html
CACTI
http://herbalistics.com.au/takeaway-tek-how-to-germinate-cacti-seeds/
ORCHIDS
-American Orchid Society Publication 'How Are Orchids Propagated?'
http://www.aos.org/orchids/additional-resources/how-are-orchids-propagated.aspx
BROMELIADS
-"Beginner’s Guide to Bromeliad Pups" Author: Melanie Dearringer
http://www.bromeliads.info/beginners-guide-bromeliad-pups/
-'POLLINATION AND HYBRIDIZATION' By: Mulford Foster
http://www.fcbs.org/articles/foster.htm
-Anwyl Bromeliad's 'Growing tillandsias from seed'
http://www.anwyl.com/articles/growing_from_seed.html
FERNS
-Fern Propagation by Spores
http://www.hardyferns.org/fern-info-propagation.php
-rabbit's foot ferns
http://www.ehow.com/how_7578099_propagate-rabbits-foot-ferns.html
PROPAGATION METHODS
ROOT CUTTINGS
http://www.finegardening.com/grow-more-plants-root-cuttings
https://www.youtube.com/watch?v=8gwCLs8LoTs
HERBACEOUS AND WOODY CUTTINGS RESOURCES
North Carolina Cooperative Extension Service Publication
Plant Propagation by Stem Cuttings: Instructions for the Home Gardener
https://content.ces.ncsu.edu/catalog/series/202/instructions-for-the-home-gardener
PROPAGATING DECIDUOUS AND EVERGREEN SHRUBS, TREES, AND VINES WITH STEM CUTTINGS
http://cru.cahe.wsu.edu/CEPublications/PNW152/PNW152.pdf
Texas A & M Propagation Manual for Trees, Shrubs and Woody Vines
Oklahoma State University Cooperative Extension Service Publication
'Propagation of Ornamental Plants for Oklahoma'
http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-9319/E-917.pdf
How to Make a Forsythe Pot
http://www.gardeningknowhow.com/garden-how-to/projects/forsythe-pot-propagation
RESOURCES - PROPAGATION BY SPECIES
Agave
http://www.birdsandblooms.com/blog/how-to-plant-agave-pups/
http://www.succulentsandmore.com/2013/10/coring-agaves-for-propagation.html
http://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1483.pdf
Aglaeonema (Chinese Evergreen)
http://mrec.ifas.ufl.edu/FoliageDigest/v4n8.html
Azalea - See Rhododendron
Buddleja/Buddleia
-cuttings
https://sites.psu.edu/plantpropagation/2014/02/25/butterfly-bush-cutting/
Calycanthus floridus
http://www.clemson.edu/extension/hgic/plants/landscape/shrubs/hgic1087.html
Callistemon
-By seed
http://anpsa.org.au/callis2.html
Carica papaya
-from cuttings
http://rfcarchives.org.au/Next/Fruits/Papaya/PawpawCuttings7-82.htm
Colocasia
http://www.hardytropicals.co.uk/page.php?id=51
Crocus
-By seed
http://www.timberpress.com/blog/2011/01/everythings-coming-up-crocuses/
'The American Horticultural Society Plant Propagation' published by Dorling Kindersley Books in 1999, with Editor-in-Chief Alan Toogood. In the UK, the same book is titled 'Royal Horticultural Society Propagating Plants'.
https://www.facebook.com/photo.php?fbid=675582972502738&set=p.675582972502738&type=3&theater?
Cycas
-Cycas revoluta (sago palm) pollination
http://www.rhapisgardens.com/sagos/sagoseed.htm
Cyperus sp.
http://www.watergardenersinternational.org/journal/3-3/dave/page1.html
https://allthedirtongardening.blogspot.com/2011/12/propagate-umbrella-palm-cyperus.html
Dahlia
HomeGuides - How to Hand Pollinate Dahlias
http://homeguides.sfgate.com/hand-pollinate-dahlias-27898.html
Eryngium foetidum (culantro)
http://www.just4growers.com/stream/troubleshooting/culantro.aspx
Fragaria (Strawberries)
http://strawberryplants.org/2010/05/strawberry-plant-propagation/
Hamamaelis (witch hazel)
http://www.clemson.edu/extension/hgic/plants/landscape/shrubs/hgic1091.html
Helleborus (Hellebore)
-From Seed
http://www.winterwoods.net/index_files/page0007.htm
Hemerocallis (Daylily) Propagation
-Beginner's Guide to Hybridizing Daylilies
http://www.ofts.com/bill/hybrdize.html
-American Hemerocallis Society Daylily Database
http://www.daylilies.org/DaylilyDB/search.php
Hibiscus
http://hibiscus-sinensis.com/cuttings.htm
Iris
-from seed
http://www.tucsoniris.org/articles/iris_from_seeds.php
Kalmia latifolia
http://scholar.lib.vt.edu/ejournals/JARS/v33n1/v33n1-fordham.htm
Laurus nobilis
http://www.omcseeds.com/laurus-nobilis-bay-laurel-5.html
Lilium
-Illustration of different types of lily bulbs
http://www.the-genus-lilium.com/bulb.htm
-Propagation by leaf cuttings
http://davesgarden.com/community/forums/t/667455/#b
-Information on Lilium species and cultivars
https://bdlilies.blogspot.com/p/lily-ratings.html
Lithodora
-L. diffusa root cuttings
http://www.srgc.net/forum/index.php?topic=11355.0
Magnolia
http://forums.gardenweb.com/forums/load/propa/msg0618055616781.html?2
http://www.dendrology.org/site/images/web4events/pdf/Tree%20info%20IDS_08_GrowingMagnolias.pdf
Malus
'Propagation of Apple Trees' by Marnie Aasheim https://www.ndsu.edu/pubweb/chiwonlee/plsc368/student/papers02/maasheim/appleprop.htm
Musa
https://www.jstor.org/stable/2439422?seq=1#page_scan_tab_contents
Nelumbo (Lotus)
https://www.victoria-adventure.org/lotus/lotus_letters1.html
Passiflora
- Rooting cuttings
http://forums.gardenweb.com/discussions/2079182/how-i-root-cuttings
Pelargonium (geranium)
-Martha Wahington geraniums
http://app-ropriate.blogspot.com/2014/09/propagation-of-martha-washington.html
-Taking leaf cuttings
http://www.gardenhousebrighton.co.uk/lost-the-plot/how-to-take-leaf-cuttings-from-pelargoniums
Petunia
-Starting from seed
http://www.ipm.iastate.edu/ipm/hortnews/2010/3-3/petunias.html
Protea
-Propagation of protea: some seeds will only sprout after exposure to smoke. The article suggests smoke primer disks, but some conifer seeds will germinate when soaked in liquid smoke from the supermarket spice aisle.
http://homeguides.sfgate.com/propagation-protea-24109.html
-Growing protea, which have unique requirements: low-nutrient soil that is acid and phosphorous-poor. http://www.rbgsyd.nsw.gov.au/plant_info/Plants_for_gardens/growing_proteas
-This article says that proteas need magnesium, and recommends Epsom salt:
http://www.abc.net.au/gardening/stories/s1976065.htm
-More specifics on propagating by cuttings.
http://www.elsenburg.com/info/els/032/032e.html
http://www.doityourself.com/stry/propagate-your-favorite-proteas#b
Quercus
https://extension.msstate.edu/sites/default/files/publications/publications/p2421_0.pdf
Rhododendron
http://www.donaldhyatt.com/garden.html
*Dormant Azalea cuttings
https://www.tjhsst.edu/~dhyatt/dormant.html
-The American Rhododendron Society - Propagation and Hybridizing
https://www.rhododendron.org/propagation.htm
Rubus
-Thornless blackberries:
*Thornless blackberries that are the result of chimerism will revert to their thorny form if propagated by root cuttings: "A classical example of an L.I periclinal chimera is the thornless blackberry. The epidermal layer of this type produces no "thorns" (the modified epidermal cells are correctly called "prickles"). The thornless epidermis covers a stem whose cells contain the information for the thorny genotype. This can be demonstrated by taking root cuttings. The adventitious shoots which differentiate on the root cuttings are not chimeral and therefore revert to the thorny genotype."
http://aggie-horticulture.tamu.edu/tisscult/Chimeras/chimeralec/chimeras.html
Thornless cultivars that are the result of a genetic mutation will retain the thornless characteristic even when propagated by root cuttings. "...genetically thornless blackberry cultivars will remain thornless whether propagated from stem cuttings, root cuttings, or suckers."
http://edis.ifas.ufl.edu/hs104
Blackberry Breeding and Genetics (Has a chart showing parentage of many blackberry cultivars and discusses breeding for certain characteristics, such as thornlessness)
Saintpaulia (African violets)
-Chimeras
http://violetvoice.yuku.com/topic/1279#.UtNYRX-9KSM
http://www.violetbarn.com/lessons/blossom_stems.htm
http://www.violetbarn.com/lessons/chimera_violets.htm
Sanguinaria canadensis
http://www.nomadseed.com/2017/06/bloodroot-sanguinaria-canadensis/
Streptocarpus
http://www.streptocarpus-info.com/streppropagation.html
https://www.youtube.com/watch?v=E4CfasShaQU&index=14
Stewartia
Tulipa (tulip)
http://lists.ibiblio.org/pipermail/pbs/2006-June/025352.html
Vitis
-Growing grapes from cuttings
http://www.bunchgrapes.com/cuttings.html
Yucca
http://www.gardeningknowhow.com/ornamental/foliage/yucca/yucca-seed-pods.htm
RESOURCES FOR VEGETABLE GARDENING - HINTS, TIPS AND ADVICE
SEED SAVING AND BREEDING
Vegetable Seed Saving Handbook
http://howtosaveseeds.com/index.php
Seed Savers Exchange Seed-Saving Guide
http://www.seedsavers.org/site/pdf/Seed%20Saving%20Guide_2017.pdf
GARDENING RESOURCES
Mother Earth News
-A Crop-by-Crop Guide to Growing Organic Vegetables and Fruits: Our Complete Crops at a Glance Guide
http://www.motherearthnews.com/crop-guide-growing-organic-vegetables-fruits-zl0z1211zsto.aspx#ixzz3EgajdkAa
CROP-SPECIFIC INFORMATION AND RESOURCES
GARLIC
Stimulating seed production
http://garlicseed.blogspot.com/p/growing-garlic-from-true-seed.html
Growing garlic from bulbils
http://www.seeds.ca/d/?t=dc88a19500003095-a275348
ONIONS
Bulb Onion Growing: Day Length and Temperature
http://www.harvesttotable.com/2012/11/bulb-onion-growing-day-length-and-temperature/
University of Georgia cooperative extension
Onion Production Guide (B 1198-2)
http://extension.uga.edu/publications/detail.cfm?number=B1198-2
De-vernalizing onions to stop bolting and restore to bulbing stage
http://ipm.missouri.edu/MPG/2010/11/Why-Onions-Bolt-Failing-to-Bulb/
and
http://www.britannica.com/EBchecked/topic/160153/devernalization
POTATOES
-Planting potatoes in Fall
http://www.backwoodshome.com/articles/williams48.html
RESOURCES FOR VEGETABLE SEED SAVERS
Info on how to collect and save seeds, storage and germination requirements, how to pollinate vegetables, how to create hybrids, and how to prevent cross-pollination.
SEED SAVING
Seed Saver's Exchange
http://www.seedsavers.org/Education/Seed-Saving-Resources/
Tomatillo Cross-pollination
http://blog.seedsavers.org/blog/tomatillopollination
Tomato Flower Types and Cross-pollination
https://papasgardens.com/2015/09/28/seed-saving-garden-basics-for-the-beginner-part-5
RESOURCES - ALL THE DIRT ABOUT SOIL AND SOILLESS MIXES
MYCORRIZAL FUNGI
EPSOM SALT
RESOURCES FOR GRAFTING
ONLINE PUBLICATIONS
Pacific Northwest Extension (WSU, OSU and UI)
Publication PNW496
'Propagation of Plants by Grafting and Budding'
https://drive.google.com/file/d/0B9fI1Pajtl8bQTRvZE9aTEEwNHc/edit
University of Minnesota
Grafting and Budding Fruit Trees
http://www.extension.umn.edu/garden/yard-garden/fruit/grafting-and-budding-fruit-trees/
Grafting and Budding Nursery Crop Plants
NC State University and A&T University Cooperative Extension
http://content.ces.ncsu.edu/grafting-and-budding-nursery-crop-plants/
Grafting Techniques
NDSU
https://www.ag.ndsu.edu/hort/info/fruit/graft/graft.htm
How to grow Your Own Root Stocks
The Walden Effect
http://www.waldeneffect.org/blog/How_to_grow_your_own_rootstocks/
Cornell Cooperative Extension
Information Bulletin 75
'Top-working and Bridge-grafting Fruit Trees'
by G. H. Overly
'Successful Apple Grafting Techniques for New York'
by Stephen A. Hoying, Alison M. DeMarree and Mario Miranda Sazo
as presented in the New York Horticultural Society's Publication 'New York Fruit Quarterly, Volume 20, Number 1, Spring 2012'
http://blogs.cornell.edu/plantpathhvl/files/2015/02/12-3-Hoying-NYFQ-grafting-28tz2tf.pdf
WEBSITES, BLOGS, FACEBOOK GROUPS, ETC.
https://www.facebook.com/groups/scionexchange/
SPECIAL APPLICATIONS
Tree peony onto herbaceous peony rootstock
https://www.treepeony.com/pages/grafting-tree-peonies
RESOURCES FOR HOME TISSUE CULTURE
WEBSITES, BLOGS, GROUPS ETC.
FACEBOOK GROUP
https://www.facebook.com/groups/PlantTCHobbyists/
Home Tissue Culture
http://www.propagatingplants.org/Home_Tissue_Culture.html
SUPPLIES, TOOLS AND EQUIPMENT
CAISSON LABS
http://www.caissonlabs.com/index.php
DIY INSTRUCTIONS
TISSUE CULTURE KIT
http://www.bghydro.com/plant-tissue-culture-kit-complete.html
DIY PLANT TISSUE CULTURE MEDIA
http://www.gardenisto.com/lab/tissue-culture/diy-plant-tissue-culture-media/
EDUCATION
LESSON PLAN ACTIVITY 5
Recipes and Methods
http://www.apsnet.org/EDCENTER/K-12/TEACHERSGUIDE/PLANTBIOTECHNOLOGY/Pages/Activity5.aspx
YOU TUBE VIDEOS
Playlist by Wynonah Bates
https://www.youtube.com/playlist?list=PLf2NfsNg_L9npBqIqeIPihOjItCpj5PpW
RESOURCES - LOW COST GREENHOUSES
MANUALS
-Hobby Greenhouses
http://extension.uga.edu/publications/detail.cfm?number=B910#Plans
-Greenhouses for Homeowners and Gardeners
http://host31.spidergraphics.com/nra/doc/Fair%20Use%20Web%20PDFs/NRAES-137_Web.pdf
-Greenhouse Engineering
http://www.hotwiredgardens.com/pdf/NRAES-033_Greenhouse_Engineering.pdf
BUILDING
-Earth Powered Greenhouses
http://www.perpetualgreengardens.com/earth-powered-greenhouses.html
-Greenhouses made from water/pop bottles
http://www.goodshomedesign.com/build-plastic-bottle-greenhouse/
-How to Build a $50 Greenhouse
http://doorgarden.com/10/50-dollar-hoop-house-green-house
-How to Build a Greenhouse with 2x4s and Cattle Panels
http://www.ericsprojects.com/?page_id=228
-How to build a $300 underground greenhouse
http://www.treehugger.com/green-architecture/build-underground-greenhouse-garden-year-round.html
-How to Build a Year-Round Solar Greenhouse
-Geothermal Greenhouses
-Greenhouse in the Snow
http://www.greenhouseinthesnow.com
http://www.youtube.com/watch?v=cT8Ic2m7voI
Cheap Homemade Greenhouses Hoop Bender
HEATING
-Temperature-controlled switches for heaters and fans
http://www.hotwiredgardens.com/pdf/Low-Cost_Control_of_heaters_and_fans_in_a_Greenhouse.pdf
Plug-in Thermostat for Heaters and Fans
http://www.northerntool.com/shop/tools/product_612108_612108
-Build a Solar Heater out of Soda Cans
http://www.goodshomedesign.com/diy-solar-panel-out-of-pop-cans/
-Using compost systems to heat water hoses for radiant heat
http://compostpower.org/node/24
RESOURCES FOR ORCHID PROPAGATION
COMPANIES SELLING PROPAGATION SUPPLIES, FLASKING SERVICES, PLANTS AND MORE
(S = Supplies, E= Equipment, F = Flasking Services, T = Educational and Instructional Materials,
P = Plants for Sale)
In Vitro Plant Service (F)
Quedlinbur , Germany
http://www.in-vitro-quedlinburg.de
Meyers Conservatory (F, P, T)
Poulsbo, Washington State, USA
Orchid Origins (F)
St. Johns, Michigan, USA
The Orchid Seedbank Project (S, P, T)
Chandler, Arizona, USA
Orchids for the People (F, P)
McKinleyville, CA
https://www.orchidpeople.com/seed-propagation
OrchidSource Laboratory and Nursery (S, F, P)
Vista, California, USA
Phytotechnology Laboratories (S, E)
Shawnee Mission, KS
https://phytotechlab.com/kits.html
Western Orchids (S, P)
Coromandel East, Australia
WEBSITES WITH PROPAGATION INSTRUCTIONS
-BY SEED, IN SITU
Growing native terrestrial orchids from seed - Dactylorhiza purpurella
http://www.leavesnbloom.com/2012/07/northern-marsh-orchid-dactylorhiza.html
-BY SEED, IN VITRO
‘Propagation Methods’ by Bill Steele of Spangle Creek Labs, a Cypripedium Nursery
http://www.spanglecreeklabs.com/lab.html
‘Home Orchid Flasking’ by Sam Fifer of Lincoln Orchid Society http://lincolnorchidsociety.org/flasking/index.html
‘Sowing Orchid Seed’ by Fred Bergman of the American Orchid Society
http://www.aos.org/AOS/media/Content-Images/PDFs/SowingOrchidSeed.pdf
-VEGETATIVE/ASEXUAL PROPAGATION
‘Propagating Orchids Vegetatively’ by Sue Bottom of the St. Augustine Orchid Society
http://staugorchidsociety.org/PDF/VegetativeReproductionofOrchidbySueBottom.pdf
-ORCHID PROPAGATION BY SPECIES
Maxillaria tenuifolia (coconut orchid)
http://www.orchidsamore.com/tutorials/Maxillaria%20tenuifloria.htm
RESOURCES - POLLEN BANKS AND EXCHANGES
Fruit and Nut Trees for Commercial Growers
American Rhododendron Society
https://www.arsoffice.org/history/pollen.htm