Continuing the sowing: in hot water

Time for more sowing and of course more seed treatments.
Technically speaking, the hot water treatment is included in the general term of seeds scarification, which also refers to the nicking/sandpapering (mechanical scarification) and the acid scarification (chemical).
They are all done for the same purpose: to weaken the seed coats and make them permeable to water and gases. They are useful for any seeds that have impermeable seed coats, regardless if warm or cold germinators.
Routinely are done for Fabaceae species, but not only. Without these treatments the seeds will still germinate but more slowly and irregular, so why waste time?

*Usually if such seeds are sown in late fall/early winter, the natural freezing and thawing cycles of winter will soften the seed coats and thus (in most cases) is not necessary to scarify the seeds before sowing.

Mechanical scarification and the hot water treatment are very easy to apply at home.

Treatment with hot (boiling) water

It just happened that I had on my sowing list a few species that require scarification, either sandpapering or the hot water treatment. For seeds of Oxytropis halleri, Hedysarum grandiflorum and Astragalus vesicarius I would usually do the scarification with sandpaper, but I don’t really like to scarify my fingers together with the small seeds, so I tried the hot water treatment this time (Feb.4-6).

The method is straightforward: place the seeds in a small container and pour boiling water on top of them; wrap it up in a cloth/aluminum foil and leave them for a day.
Next day, due to minuscule fissures in the seeds coat, the seeds should look swollen, sometimes 2-3 times the original size. The treatment can be repeated if necessary.

Using the hot water treatment I obtained the same amount of swollen seeds as when using sandpaper, so I’m glad it works even if partially. Not two seeds are the same ;) of course, most surely as an adaptation of not having all seeds germinating at the same time (i.e. all seedlings destroyed in case of unfavorable conditions).

Sow the seeds right away and water very well. It is important not to let the seeds dry out after they got imbibed with water. Place the pots at warm or at cold if cold/moist stratification is required.

I also used this method for a couple of yellow flowered Baptisia cultivars I acquired from ORG&HP Society seed exchange. Most probably they won’t come completely true from seeds (being hybrids) but by any other colour will look well together with Baptisia australis. One can never have enough Baptisia plants in the garden.

Mechanical scarification

It is done for the same purpose of ‘eroding’ the seed coat to allow water and gases imbibition. Most usual is to rub the seeds between 2 pieces of sandpaper for a few seconds or longer (use the medium or fine grind).
For small seeds, it’s easier said than done because one cannot observe if they were scarified enough or too much. Remember from the nicking when I mentioned that hard seed coats don’t thicken uniformly? It is better to scarify less than too much. I always place the seeds afterwards in a moist towel for a day or two to make sure that the seed coats were well scratched (the seeds should look swollen); if not, repeat again.

For larger seeds doing this is much easier and you can even employ a metal file. I didn’t take a picture of the filed seeds when I did this for

Triosteum aurantiacum fruits. I’ve shown them recently in cross section; the extremely thick tegument would  need a few good years to break down in a natural way in the soil.
The well scarified fruits placed in cold/moist stratification afterwards, will lead to an acceptable germination in the following spring. You can see the result in the image, the seedlings grow fast, they were planted in the ground last fall.

 

Chemical scarification
For species with extremely hard seed coats, chemical scarification by use of acids is recommended but in my opinion it is not doable for home use and I won’t detailed it.
At home, you can always try the regular scarification for species where acid scarification is recommended. Even if not entirely effective, it will help partially in thinning the seed coats.
For example, acid scarification is known to improve the germination for Rubus species.

Among the species which would benefit from these treatments: Amphicarpaea, Dalea, Lupinus, Oxytropis, Astragalus, Hedysarum, Lespedeza, Ceanothus, Cercis, Triosteum, Gleditsia,…..to mention just a few.

Happy treating/sowing!

Updates for the hot water treatment – one week later (Feb. 12)

Although it is necessary to repeat the treatment because not all seeds will imbibe after a first soak, overall this is a very easy and effective treatment.
I recommend it for all the species in Fabaceae family.
In some cases the seeds may even start to germinate in the water (when repeating the treatment).

 

Updates: see how some of the species shown here (and others) are looking later in March.
Updates for the hot water treatment
Friday’s hairy seedlings