A PRACTICAL GUIDE TO GERMINATING PLANT SEEDS
(reprinted from Pritchardia, April 2000)
Jeff Marcus and Ken Banks with Bill Austin (revised from Palms)
With most palms, propagation from seed is not difficult as long as a few basic requirements are met. Among the most important are fresh seed, good sanitation, proper medium, proper hydration, and adequate heat. Each of these points will be discussed separately, although they are interrelated.
The fresher the seeds are, the better the results will be. To check the freshness of your seeds, cut open a sample seed and inspect the endosperm and embryo. The embryo should be fresh, firm, and not discolored. If the interior of the seed is rotten or has an unpleasant odor, it is unlikely to germinate. The endosperm is of two types, homogenous or ruminant, and may be hard, oily, or even hollow. The term homogeneous means that the endosperm is uniform and appears as a single, even color, usually white or cream. In a ruminant seed, the seed coat is info!ded, creating dark, tangled streaks in the endosperm. If the inside of a homogeneous seed is off-color, such as brown or gray, or if it smells bad, then the seed is old or was harvested before maturity. Such seeds are also unlikely to germinate. Ruminant seed is more difficult to assess because of its more complex appearance.
Removing the Fruit Pulp
The fleshy or fibrous fruit pulp frequently contains growth inhibitors. Removing it before planting will improve results. Methods for doing this vary with the quantity and type of seeds, but most begin with a preliminary 48-72 hour soak in water. Soaking causes the pulp to ferment, which weakens it for easier removal. Change the water daily during the soak. If the fruit is slightly immature, it should be placed in a tightly closed plastic bag and kept in a warm spot for a week or so. This promotes ripening and softens the outer flesh for cleaning. Sometimes the immature seeds also need to be soaked to soften the pulp, sometimes not.
There are several ways to remove the seed coat. With small quantities of seeds, simply rub them by hand against a fine-meshed screen and wash away the pulp with water. Another way that works well with small amounts of seed is to shake them by hand in a closed container with water and small, rough-edged rocks. Pour off the water and pulp occasionally, add more water and shake again, until the seeds are completely clean. Seeds can also be cleaned with a knife or other sharp tool, but this is slow and can be dangerous.
Motorized cleaning devices make the job easier and are a necessity for commercial operations. For smaller quantities, use a rock tumbler. Put rocks and water inside with the seeds. The seeds are rotated in the drum for 10 to 45 minutes with water and rough-edged rocks of 7 to 10 cm. The time will vary with the machine and the type of seed and rocks. Some seeds are brittle, and without proper care may be damaged by power cleaning. Among large-seeded palms, Actinorhytis is particularly brittle and prone to damage, and many smaller seeds, such as Pinanga, must also be handled with care. When cleaning seeds, remember that the flesh of some types contain crystals of calcium oxalate, a skin irritant that can cause severe pain on contact, depending on the individual's sensitivity. Ptychosperma, Arenga, Caryota, and Wa/lichia should be handled with care. An additional note for seed collectors: avoid looking directly up into the infructescences of these palms when attempting to knock down or cut down fruit. The irritating crystals may fall into your eyes.
Damaging insects such as seed-boring beetles may arrive with seeds. They may reduce germination and spread to other seed
batches. To minimize these risks, seeds collected from the ground, whether in the wild or from cultivated plants, and seeds
collected under unknown conditions should be soaked in a contact insecticide solution once the frui~ pulp has been removed. The
insecticide solution should be prepared at the same concentration you would use to spray for pests.
Soak small, thinner-shelled
seed, such as Pinanga, for 15 minutes. Soak larger, harder and less permeable seeds longer, from 20 to 45 minutes. Examples of
these latter seeds are Mauritia flexuosa, Bismarckia nobflis, Parajubea cocoides, and Jubea chi/iensis. After the insecticide soak,
rinse the seeds in clean water for 20 minutes.
After cleaning the seeds, hydrate them by soaking it in water for 24 hours, especially if you did not soak them to help remove the
pulp. Within 24 hours most fresh, viable seeds will sink. There are exceptions such as Manicaria saccifera and Metroxylon
vitiense, whose viable seed will float even after cleaning and soaking.
Whether or not to discard a batch of heavily infested, damaged seeds depends on their rarity and your ability to get more. For
very rare seeds, when even a single germination would be valuable, plant it. Remember, however, with heavily infested seeds,
especially in large quantities, there is the danger of introducing pests into your nursery. Balance this risk against the desirability
of propagating the seeds and follow the treatment procedures described above.
Fungi flourish in the heat and humidity necessary for good germination, so equipment, fixtures, seeds and growing medium must
be kept clean to prevent damping-off and other disease problems. You may want to soak seed in a fungicide before planting.
Germinate the easy varieties in containers, in a commercial mix of peat moss or sterile sphagnum moss mixed with an equal
amount of perlite or vermiculite. You may also use commercially prepared, finely cut coconut coir to which the same fast-draining
material has been added. Sand, wood chips, screened rock or volcanic cinder screened to a maximum size of 3/8 inch can substitute for vermiculite or perlite. Whatever you use, the medium should be very porous and drain extremely well. All
containers should have plenty of holes in the bottom to ensure quick and thorough drainage.
When containers and planting medium are ready, lay out the seeds on the surface, and before covering them, dust with a
commercial insecticide. Bury the seeds in the medium to a depth of half the seed diameter and then cover everything with finely screened cinder (1/8 to l/4 inch particle size), thick enough so it will not wash away during watering. This topdressing dries out quickly and discourages the moss that grows on peat. Sand or finely crushed rock would work just as well. When planting is complete, place the containers on clean benches, 24-36 inches above the ground. Be sure to label your containers with a waterproof and fade-proof marker (a soft-lead pencil works well).
Palm seeds known as remote germinators may require special treatment and a little extra patience. Examples of remote germinators are Kerriodoxa elegans, Caryota, Arenga, Orania, Coccothrinax and Copernicia. Remote germinators send a radical (first root) downwards as much as 8-10 inches before sending up the first leaf. The larger ones, such as Voanioala and Borassodendron.t. should be planted in deep containers such as citrus bags or large tubs, or be transferred to such containers soon after germination. If seeds and seedlings can be protected, the collector may want to plant large remote-germinators directly in the ground.
Hydration and Heat
At this point, the most important factor in seed germination is proper hydration, followed by constant high heat. Maintaining
proper hydration is the trickiest of the two. Water your containers thoroughly, but just as important, let them dry out thoroughly before watering again. Over-hydration can drastically reduce the germination percentage. Once seeds begin to germinate, the containers will require more frequent watering. Seeds should be kept between 78 degrees and 95 degrees F. Some growers provide constant bottom heat by means of electric pads on their benches.
For difficult seeds and rare seeds, the most reliable method of germination is the "Plastic Bag Method." For this method, seeds are blanketed in damp sphagnum moss and germinated in zipper-type, re-sealable plastic bags. Thoroughly saturate the sphagnum moss with water and wring it until no more can be expressed. Use scissors or shears to cut up the long strings of moss. It makes it easier to handle. Place a layer of moss in the bottom of the bag. It should be loosely placed, not packed in. Then place the seeds on top of the moss (there is no need to arrange them over-neatly in rows). If there are more seeds than can be placed on the moss without piling them, add more moss and the remaining seed. Cover the top layer of seed. Use as many layers as
necessary, remembering not to pack the bag tightly.
Keep the seed bags (along with a label) at 78 to 95 degrees F. Bags should be checked about every two weeks by opening them and carefully examining the seed. Sometimes lt is necessary to work at a table, gently pulling out the moss and looking through it. It is important to check bags regularly, as germination times can vary greatly from published information and germination can be sporadic. According to Bill Austin, Licuala and Coccothrinax are among the trickiest germinators. Out of 500 seeds, a handful might germinate in 4 or 5 months, while the rest may take another 9 months to a year. Don't give up on seed too early.
Once seeds have germinated, place them in community or individual pots containing the potting mix described above and the
quick-drying top-dressing. After transferring germinating seed from the relatively sanitary conditions inside the bags to pots containing ordinary medium, treat them to a precautionary fungicide drench. It may be advisable to leave some small seed in the bag for a short period after it has germinated. This allows it to attain some size and increases the survival rate.
When in the germination area and when checking seed, watch for bags in which the moss may be drying out. Condensation on
the inside of the bag indicates that it is adequately hydrated; bags lacking condensation should be checked more closely. If the moss is dry, remove it from the bag, separate it from the seed, and drizzle enough water on it to re-hydrate. "Lomi Lom;" (massage) the moss after drizzling, to distribute the water evenly. Squeeze it out if there is excess water, being careful not to damage any seed that may still be in it.
A final method (if can be called a method) is simply to germinate the seed on the ground in an out-of-the-way part of the greenhouse or garden. Growers have had good results this way with Pelaqodoxa henryana, Jubea chilensis, and some Acrocomia species. Discarded seed has also been found germinating in many a surprised grower's compost pile.