by Joe Coleman
One of the easiest methods of propagating azaleas and other rhododendrons is from seeds. Seed from these kinds of plants do not require any special scarification, stratification, or other pre-treatment. Unless the seed is from an unusual hybrid, it will probably germinate readily, and seed sown in the winter should be in quart or gallon pots by the next fall. Seedlings obtain their chromosomes and thus their characteristics from both the pollen parent and the seed parent. If both parents are of the same species, the seedlings will be similar but vary within the bounds of the characteristics of that particular species. If the parents are different species, some seedlings will look more like one or the other parent and some may share characteristics of both parents. For example, pollen from an orange R. flammeum (Oconee Azalea) placed on a pink R. canescens (Piedmont Azalea) may produce some pink seedlings with a strong gold blotch as well as some canescens-looking and flammeum-looking plants.
The following seed-propagation information is primarily geared to the greater Atlanta area in the southeastern part of the U.S. and for the climatic conditions and tools available to the Azalea Chapter of the American Rhododendron Society. There are multiple variations, but this system has proven quite successful. Practice this a few times, and you will soon become an expert. These techniques apply to seed from native azaleas, evergreen azaleas, and other rhododendron. Size of seed varies. As a general rule, seed from evergreen azaleas is the smallest, native azalea seed is middle sized, and seed from other rhododendron is the largest. Most deciduous and rhododendron seeds are elongated (elliptical), while evergreen azalea seeds appear to be small balls. All, however, are quite small. One seed pod may have as many as 200 seeds.
Preparing the Seed
- Collect the evergreen or deciduous seed pods. This is primarily done in October before the first good hard freezes occur and the pods open naturally. I use old paper envelopes left over from my office, and being paper, the pods can dry out. It is essential to identify by writing on the envelope the type of pods gathered. Other good info to note on the envelope is the source, location gathered, probable cross, plus any details about the site or size of plant. If you are collecting in wet conditions, use some zip-seal bags to gather each batch and place a label inside the bag – later they can be transferred to paper for faster drying. If out collecting in a dense fog on a mountain top, paper envelopes have a tendency to get totally wet and disintegrate, so be prepared for your conditions.
- Drying seed pods is best done over a period of several weeks. Desiccants, both chemical from a pharmacy or powdered milk, can speed up the process, but merely being in a warm place with low humidity will do the trick. Trying to clean wet or moist pods is simply self defeating. Wait until they are dry.
- Once the pods are dry, the next step is to collect the individual seeds from the seed pods. Simply, this is accomplished by using a series of mesh strainers of smaller and smaller sizes to separate the chaff from the seed. Materials for use:
- A folded section of newspaper protects the kitchen counter and helps to protect the zip-seal bag that is placed between the two layers of newsprint.
- A freezer zip-seal bag. It’s tough and can take abuse of being pounded a number of times. Choose a size that fits the size of the job you are doing, allowing the seed to be spread out for shattering.
- A rubber mallet with a large striking surface. A hammer will do if small. I do not recommend a rolling pin. It will not crush the pods.
- Several mesh strainers of different sizes to remove debris, found at any local grocery store or gourmet kitchen supply. Professional sets are available, but are expensive. Three to five different sizes can accommodate most seed. Professionals use up to five, but these experts work with a wide variety of seed sizes. Try window screen for a first sifting and then get progressively smaller. The last size should allow just the dust through, leaving fairly clean seed. Evergreen azalea seed may require a very small mesh strainer. The less chaff and dust you have with the seed, the less chance you will have of fungus contaminating the seed. The cleaner the better!
- A nearby waste basket to dump the debris with each sifting.
Clean coin envelopes or containers for seed storage. These are easy to obtain from local office supply dealers and can be individually labeled as you process the seed.- Two pieces of white paper to work on. You can see seed better on white, and it helps in identifying what is seed and what is debris.
- A sense of real aggression, as crushing seed pods takes real force, no delicate tapping. After the first session of pounding, agitate the zip-seal and pound again. Small evergreen azalea seed pods can be hard and tough to break down. Not everyone crushes the pods as indelicately as I do. Some people have more time and patience so they cut each pod and try to shake out the seed, avoiding the issue of a lot of dust. But the simple and quick pounding method works well.
- A folded section of newspaper protects the kitchen counter and helps to protect the zip-seal bag that is placed between the two layers of newsprint.
- Empty the dried seed pods into the thick (freezer) zip-seal bag, place it inside the fold of newspaper and pound away several times until all the pods are crushed and no intact pods can be seen. Turn the zip-seal over and pound again, so that no intact pod is evident when you open the bag.
- Place your largest mesh screen, usually window screen, over your first piece of white paper and dump the contents of the zip-seal onto it.
- Agitate the screen until nothing more sifts through. The seed will go through the mesh, leaving the chaff in the screen, which is then dumped into the wastebasket at your feet.
- Using progressively smaller mesh, repeat the sifting process several times, getting rid of the obvious chaff. Repeating the process produces cleaner seed.
- There will still be a lot of dust in the mix, so go to the smallest screen and shake all the dust through the screen and onto the second piece of white paper. At this stage, the seed should remain in the strainer, and the dust should be discarded. Remember the chaff remains in the initial, larger mesh screenings and the small seeds strain through, but only the seeds remain in the last, smallest mesh screening. Don’t thrown the wrong portion away here.
- Pour the seed into labeled coin envelopes, unless you are going to sow it shortly. Seed can be refrigerated for those species that benefit from a period of stratification, just as Mother Nature does. Seed can also be frozen for some years, but there is a decrease in its viability over time.
Sewing Seed
Prepare seed boxes a few days before sowing seed to allow moisture to settle in the seed starting mix. I use the clear plastic bakery containers from the grocery store, as they seal very tight to retain moisture, and they are free! Visit the bakery early when they are baking, and if you ask nicely, they may even give you a clean container or two to use. They come in many sizes and dimensions, depending on your needs and amount of seeds.
At this time, I do not punch drain holes in the bottom of the containers. Some use commercially available 10 x 20 in (25 x 51 cm) flats with inserts that enable separation of the different species sown. One choice is an insert that provides eight 5 x 5 in (13 x 13 cm) containers. Clear plastic covers are available that cover the flat and keep the medium from drying out. The flats used do not have bottom holes. Duct tape can be wrapped around the cover, holding it securely to the flat.
- Fill the bottom half with a mixture of perlite and fine pine bark with a light covering of screened or milled sphagnum moss on top. The moss is naturally fungicidal and moisture retentive. You can use just regular sphagnum, but the surface is rather irregular and more difficult to keep uniformly moist. I like the roots to go down easily into the bark-perlite mix. Any moist medium substitute should work, such as coconut coir, but if using Canadian peat, just be aware of the difficulty of re-wetting it in the heat of the Deep South. In the south – by which I mean hot and dry summers and fall – the use of peat is contraindicated, as once it dries out, it is almost impossible to re-wet before the seedlings die.
- The box should be moist, not standing in water. Pour off any excess water. Sprinkle the seed on the surface. [advice on how much seed to sprinkle?]
- Label each container or row in the container. It is always nice to know as much information as you have on the seed type, source, origin, cross, etc. Keep your guess work to a minimum. If you are not thorough, you may end up with a world class seedling and then don’t remember any details about the seed.
- Just before closure, I give a last minute misting to settle the seed lightly in. I use a mist of Consan® 20, which is a fungicidal soap to prevent black mold growth that can take out an entire seed container quickly - any good fungicide should do the job. Fungicides go out of fashion as newer, pricier products come on the market, but sometimes the older products can do the job nicely.
- Place the sealed seed box under fluorescent lights, 10 in (25 cm) or more from the bulbs. Mine are in an unheated basement, but the furnace keeps the area in the 50s to 60s F (10-15 C). Faster growth would occur at about 70 F (21 C). Just remember, plants do quite well in the spring and the fall at moderate temperature, and so will seedlings. Bottom heat can be obtained from heating pads, with build in thermostats, designed to heat flats. However, these pads can be expensive with a pad that will heat a single 10 x 20 in (25 x 50 cm) flat costing approximately $30. A more economical alternative is heating cables that will heat a larger area. A cable 48 ft long will heat about 12 sq ft and costs about $40. These cables usually have a built in a 70 degree (21 C) thermostat. Some cables sold lack thermostats and must be used with external units. The cables are spread on a flat surface, usually plywood, and held down with duct tape. Bottom heat does speed up seed germination.
- After the seeds sprout and young green leaves are up and hitting the lid, I simply cut off the lid, and with an ice pick I punch drainage holes in the bottom of the container. This allows for daily misting, and the seedlings begin to acclimate (in place) to more normal growing conditions.
- After the seedlings are established and comfortable with the humidity in the basement, I can then fertilize with liquid fertilizer, half strength or even less – anything mild will do. Plants do not read or appreciate attractive pictures on fertilizer containers, so fertilize lightly and be consistent.
- Springtime is the time to move the seedlings outside to the real world. Usually, I prepare a flat of 36 cells with a mixture of pine bark soil conditioner (fine pine bark) with the addition a little gypsum, trace elements (since pine bark has nothing to add to development), and sometimes very little perlite to maintain good drainage and oxygen space. I then moisten the medium. Seedlings can be gently teased up from the germination medium using a fork, pencil, or dibble and inserted into the new growing medium. Take care to hold each seedling by a leaf and not by the young stem when transplanting to avoid damaging its vascular system.
- Watering the new trays is best done by misting, so that the seedlings do not get flattened and are allowed to gain strength. Don’t be in too great a hurry to fertilize right after transplanting. There is plenty of time, and half strength on a regular schedule will insure a healthy plant before the end of summer.
- By summer’s end, deciduous azaleas as well as evergreen azaleas should be six or more inches (15 cm) high, their trays moved outside under shade protection, to allow for acclimating. From the 36 cell tray, they should be transferred to quart or gallon containers, depending on their growth. At this time, fertilization should be stopped and the natural flow of growth and winterization allowed to take place.
Conclusion
Please note: There are many, many variances in technique and materials in starting seed, depending on what you have to work with. An automatic mist system in a warm green house, allows you to use trays of moist peat under the mist system. The advantage is just slipping the seedlings up and out of the medium as you need them. Seed can also be started in a sealed transparent box on a north-facing window sill. Cold frames are useful but slower.
The key to success is to keep an eye on them, checking periodically on moisture and any growth of fungi. When in doubt, don't fertilize, and when you do, lightly is always better. Remember, you are not selling fertilizer, just using it!
