I reported in an earlier article on Professor Roger Koide’s discovery that flowering maple (Abutilon spp) seeds sprout best when soaked in 140-degree-Fahrenheit water before planting. After this worked for me, I wondered whether the treatment might soften up other hard-shelled members of the mallow family too. Through experimentation over the last couple years, I’ve determined that it seems to speed and/or improve germination of abelmoschus and some African hibiscus species—especially those with small, hard seeds.
Get Into Hot Water: Softening Up Tough Seeds
Although the professor recommended a 140-degree soak that lasted for ten minutes, I use a slightly different method. First, I put the tea kettle on and mark several Styrofoam cups with the names of the species I intend to treat. Once the kettle whistles, I pour boiling water into each cup and employ a candy thermometer to determine when the temperature of that water has fallen to 140 degrees. After dropping the seeds into their hot bath at that point, I allow them to soak in the cooling water overnight before sowing them.
Come To a Boil: Cracking Recalcitrant Seeds
The hot water method isn’t foolproof, of course. Take abelmoschus species, for example. The red-flowered ‘Lil Mischief’ and a yellow-flowered sagittifolius type, such as the one above, popped right up with that treatment, as did esculentus (okra). But the seeds of ‘Pacific Pink’ failed to respond at all. So I decided to try boiling water on them. Sure enough, they then sprouted in two days.
Other tough “nuts to crack” for which boiling water often is recommended include acacia, canna, chorizema, gunnera, and pentapetes. Keep in mind that the water only should be boiling at the time you pour it over the seeds. You then can allow it—and them—to cool off. Because boiling water may cook— rather than simply crack—softer seeds, be careful to only use it on hardcases! Those which have been given such extreme treatment tend to germinate quickly, often within two or three days of being sown.
Soaked to the Skin: Moisturizing Less Resistant Seeds
Many other species also sprout faster after being immersed in lukewarm water overnight, with some doing best if smoke or gibberellic acid is added to their bath water. However, I don't recommend the pre-sowing treatment for very small seeds, which will stick to their container or each other and be difficult to scatter when wet.
Morning glories--such as the one in the banner photo--and sweet peas usually will germinate in 4 to 7 days after an overnight soak. However, there are a few species types of morning glories which have very hard and/or fuzzy seeds. It often is a good idea to nick a tiny chip out of each of those with the tip of a utility knife before soaking them. You can use needle nose pliers to hold the seed, so that you don’t endanger your fingers.
To determine whether or not your seeds need the knife, note whether or not they swell up (increase in size) after being immersed in water overnight. If they don’t, they probably aren’t absorbing that water and should be nicked to allow it to ooze in.
All Washed Up: Cleaning Fruit Pulp from Seeds
So we can conclude that it's not only the seeds of flowering maples, such as the one pictured above, which can profit from baths. I would especially recommend pre-sowing dunkings for tropical seeds and those which just have been removed from fruits. For the latter, germination genius Norman Deno often recommended a week long soak--with changes of water three times per day--to wash away pulp and germination inhibitors. If you are planting fruit seeds which already have been cleaned by someone else, you shouldn’t need to bother with this process.
The easiest way to soak most seeds is simply to pour a little lukewarm water into the tiny ziplock baggie in which they are contained. Of course, that only works for me because I get a lot of my seeds in trade from other gardeners who use those baggies. So, if all your packets are paper, you may want to clean and save your Styrofoam coffee cups for reuse as seed saturators.
Photos: The photos included in the article are my own.