I have some old black raspberry seed I have kept in a refrigerator for a few years. The plant I collected it from was spine-less and very vigorous. I had donated some to Oregon State, and recently read in a publication from that study, that this particular seed lot produced a large percentage of spine-less seedlings. Since I lost the original tip-rooted plant, and the original was destroyed, I thought I would try to germ some seeds. According to this paper, old R. occidentalis seed needs more extreme measures for germination. They found that 3 hours in 98% sulfuric acid was required. 30 minutes in bleach did nothing, and 30 minutes sulfuric did very little (<10% germination). āSmoke waterā also had some positive effects. If you do try concentrated sulfuric acid, be sure to add seeds that are completely dry to the acid, or the heat generated will kill the embryos. Also, placing the tube in an ice-bath can help protect seeds from heat. Old seeds will also need cold stratification after scarification (fresh dry seeds harvested within 2-3 days do not).
I tried this and the seeds are now in cold stratification. Iāll be impressed if it works, as the seeds are 15 years old.
I do know a couple of things of what not to doā¦ when it comes to Rubus.
1)drying seems to kill them. I found a guy with a very obscure raspberry and he insists on drying them. He notes that everyone that sells seeds online sells them dried. Every dried seed that i have received floats and does not germinate. Perhaps there are cases where they doā¦ but i have not found that to happen with my trials. I asked him to do a simple float test before sending me seedsā¦ and not send me seeds that floatedā¦ he is intent on proving me wrong and will not send me seeds now. He is 2 years into trying to germinate his dried seeds. Pity.
2)bleach- yes 30 mins is not enough. 4hrs is a better soak time. After 4 hrs a decline. (perhaps this is how long that the seeds are also in the stomach of birds etc?)
seeds germinate better in darkness. I lost a tray a few years back because i planted too shallow and put them out on the sunporch. Further reading states that best germination occurs in darknessā¦ so i planted deeper and placed trays in the shade.
Drying doesnāt kill rubus seeds but puts them into a state called double dormancy where the seed endocarp hardens preventing germination. Sulphuric acid is used for this reason. Floating seeds might be duds but I usually sow every single one regardless as Iāve found this rule not to be 100% accurate. I never gave much thought to whether the seeds float or not but I wouldnāt be surprised if a number of them would eventually sink after soaking.
I usually plant my seeds fresh to avoid all the hassle.
Do you use hydrogen peroxide from a supermarket / pharmacy? Or do you buy a more concentrated form from a specialty / online store? I got an old bottle here (perhaps I should buy a new one) that says itās 3% concentration. Given the choice, Iād much rather use H2O2 than sulfuric acid.
And how is it used? Soaking the dried seed prior to stratification, or soaking it post-stratification? Any rinsing after the soak or other additional steps?
The way Iād stratify is prepare a 4in nursery pot, bury the seeds for a month, then refrigerate the pot in a ziplock bag for winter (Āæ3 months?).
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I have seeds for:
R. chamaemorus (8x)
R. caesius (4x)
R. roseus (6x)
R. odoratus (2x)
And the following Idaeobatus (2x):
R. coreanus
R. corchorifolius
R. crataegifolius
R. hawaiensis
R. spectabilis
R. rosifolius
R. ellipticus
R. niveus
Iām particularly keen on working with R. roseus. On the tropical side, ellipticus, niveus and rosifolius seem particularly promising (R. probus wouldāve been better than rosifolius, but I can re-acquire that in my local mountains). Coreanus, crataegifolius and odoratus all seem promising on the temperate side of the equation. As for R. hawaiensis, Iām a bit concerned that prior breeding attempts with it have produced bitter berriesā¦ Iām thinking to crossbreed it with its closest relative, spectabilis, and then select for flavor and growing traits after backcrossing a bit.
Does the H2O2 method work on dry seeds, or would sulfuric acid be preferred for those? Iām pretty sure my seeds have spent years dried at Corvallis, and I currently have them in the freezer.
Im no expert. I just know that acid, bleach, hot water and peroxide can all be used to scarify. Each with its own timeframe.
No clue on the dry seedsā¦ i just know that in nature and in the study that i posted a link to that drying decreases germinationā¦ to what end or timeframe i do not know. (as far as Rubus is concerned).
As to the freezer part- i guess they can last decades? This place sells seeds that are frozen and encourages freezingā¦not sure of the science on that though.
Iām not, I read the article, but have not had any problems with germination or lack of vigor in peach seedlings. About one of the easiest seeds to germinate.
I got another packet of Rubus glaucus in the mail today, from eBay. Before I start experimenting with my Corvallis seed, Iām gonna try this. Tomorrow, if Iām able, otherwise Monday.
