Black locust (robinia pseudoacacia) propagation problems

Hi all,

I'm a big fan of robinia and have been trying to propagate them from seed. Initially I was very ignorant and wondered why the seeds didn't germinate at all. Then after some research I tried to scarify them with hot water and that helped a little bit, but still the germination rate wasn't great. Then I followed Mudge and Gabriel's advice in their book Farming the Woods , which is to leave them in sulfuric acid for 1.5 hr. Germination rate is again slightly better but still not great. I'm getting like 25 trees from hundreds of seeds, so let's say a 10/20% germination rate. In the book it seems as if Mudge and Gabriel get near 100% germination rate.

Any advice?

Maybe the season is not right, and I should wait until it gets warmer? it's about 15/20 degrees during the day and about 10 during the night. It's been rather chilly (for the south of France) and a lot of rain.

I'm in the south of france and robinia grows like weed here everywhere. Digging out small robinia's next to the road also works alright but we need more and I still want to grow from seed.

Thanks.
Han  

I get very good germination rates with cold stratification. I just put a bunch in a big pot, leave them over the winter and separate them in the spring

I put a bunch of them in a bowl in the refrigerator and when I want to plant them in the spring, I bring a pan of water to a boil, take the pan off the heat, and throw a bunch of seeds in.  I leave them 24 hours.  At that time, the ones that have swollen, I plant.  The ones that haven't, I do it again.  I have very good germination, at least 80% I would guess, probably higher.

Okay, I suppose I will try to soak the seeds that did not germinate in hot water again. It doesn't seem like Robinia needs cold stratification, as far as I know it's a legume and they rarely need cold stratification.

10-20% germinationrate isn’t terrible. I hope i can get that. I’ve put a ladder against an interesting looking acacia of my neighbor and cut some branches off with a battery jigsaw. Collected the seeds of the branches. If you get no luck with upping the rates get moaaar.
I am north of you and haven’t seen a single one sprout so far. But the weather is very very cold for this time of year. Hope it’s that and not a 0% germination rate.
Do snails fancy young acacia sprouts, anyone know?

When I purchased seeds from Sheffields they went into the fridge for a while, so 35-40F, until I was ready to plant and then I boiled water, poured it into a ceramic cup and then added seeds for 1 day. The swollen ones were put in pots and it was definitely over 90% germination. I don't believe they have a tap root so transplanting doesn't risk damaging that. Harvesting fresh seeds might need different handling, I have no experience with that.

@Hugo Morvan snails do eat them a bit, but with mine they only got to them when they were a bit bigger already and in general they're very tough trees and it doesn't bother them much.

And yes transplanting is no problem, in fact I've heard they can regrow just from a peace of root. I haven't tried that yet but my friend had dug out like 20 last winter, cutting most of the roots and only leaving a bit of root on them, and they all seem to have survived easily.

I had one volunteer in my front yard.
I knew it couldn't stay so my son got to chop it down with hatchet, the beautiful "Bella".
The branches went into a sub irrigated planter for a couple of months.
Last week I repotted the ones with leaves and cut up the rest for kindling.

Since they grow wild near you, maybe take a bunch of cuttings along side your seed starting efforts.

I actually live in a black locust grove in it native range and I just dig them up. They grow so fast here in the wetlands, or probably anywhere. Considering you're doing so many I can see why if would be frustrating digging all of them by hand. I assume in my case usually I am seeing suckers, but also I assume the seeds just ride out a general cold stratification, without much hassle. So you might try to refrigerate the seeds for 3 months.

Kevin. Good for you! I wish i could just dig them out, it’s rocky and tiring time consuming business where i am!
If you need a few hundred it’s not an option. I am sure you can see the allure in cleaning a piece of land adding straw, dumping compost and hotwatered seeds, walk off and come back and harvest fifty trees frim the soft compost in an hour in autumn.
At least that’s what i’m hoping for. Haha!
I went for a peak yesterday but nothings popping so far. No ash either, no plums, no hazels, no sweet chestnuts, the cuttings are slow too. Last year the willow was booming around this point in time, this year they’re timidly showing some foliage half expecting to be hammered back by some late crazy frost. Oddly enough mimicking the folk getting out and about unsure after month of masking up and home detention.
Nature is such a teacher!

Thank you all for your contributions. I'm sure we will all succesfully grow many forests of Robina soon, and so here is a nice video by Edible Acres on how to manage a Robinia coppice.

https://www.youtube.com/watch?v=OpqJsLzEbQ0

Edit: I will also try soaking them much longer in water, for a few days, as was mentioned here:
https://permies.com/t/60907/Planting-black-locust-quantity-simply
"I germinated about fifty plants last year. I tried three methods:  plant without any treatment, cover in boiling water and sit for 24 hours, cover in boiling water and sit for several days (I think 4-6). I had by far the best result with option three"

Yeah most transplanting in the wetlands here happens in Spring as despite the location the heavy clay does harden to brick in July and August. If it were me I'd bag a lot of seed and dry cold stratify them.

I read that cutting into the shell (scarification) plus  hot water soaking overnight, then planting the swollen seeds is the way to go, so I recently tried it with a seed pod I had picked up off the ground last year in the next town.  

I had to use needle nose pliers and a jewelry saw to cut into the super hard seed shell (not too deep, not too shallow!).  The swollen seeds were planted on June 7 but no signs of anything yet.  Given the drought situation here, maybe this isn't the best time to try growing black locust, but then they're supposed to be tough and I have hopes that if they sprout some will live to grow into trees.

Dear all,

After more trials I can confirm what other have said, the trick is really to get them to swell. I have been able to get near 100% germination rate with swollen seeds.
I have trialed the swollen VS not-swollen seeds and you can see the result in the image attached: one with near 100% sprouts and one with zero.

>Poor boiling water on the seeds and leave them for the night.
>The next day, pick out the swollen ones and plant them. For the non-swollen ones, again poor boiling water and leave for the night. Just keep repeating until they are all swollen.

Before they are swollen my seeds are slightly greyish with black dots on then, When they swell they become bigger, slightly greenish and seem to loose their black spots. (see the two images attached: the swollen and non-swollen ones have been separated)

Other tentative conclusions to this experiment:
-All my seeds had been stratified with sulfuric acid as instructed by Mudge and Gabriel's in Farming the Woods  for 1.5 hr. This does not seem to do much for me.
-I see no reason to believe cold-stratification would have any influence. No need.

I have not been able to find these detailed instructions anywhere in the literature.

Hope this works for others as well, let us know!

PS. I had grown the swollen seeds in a small yoghurt container and after they were about 5 cm high I transplanted them to a bigger container. I might have done something wrong, but in any case they didn't like it and about 50% didn't make it. So I can recommend to seed immediately in a larger container or directly in the soil in a growing bed or it's final location. The snails might get one or two so just plant a couple. If the snails get to them when they only have their first 2 leaves they ight not make it (although some recover even from that). Once they grow to 10cm and have a bunch of leaves, snails might nibble on a few leaves but that doesn't matter much and they quickly grow new ones.  

I've had pretty good success using a file to scarify the seeds--but I don't do many seeds at a time.
The most I've done in one sitting is about 30 seeds. If you are planning to scarify many seeds at a time, this manual labour method probably is not appropriate for you.

First, I put down a few sheets of white paper. The seeds are always slipping out of my fingers; the contrast of black seed on white background makes it easier to find the seed when that happens.

Second, each side of each seed gets about twenty rubs across the file. Sometimes I get lucky and a seed doesn't need twenty strokes. Sometimes I see the white inside of the seed before twenty, so I stop. All that is required is that the waterproof coating of the seed be unsealed so that water can be absorbed by the seed and it swells.

Third, the seeds are put in a shot glass of water. Cold water straight out of the tap. The intention is to let them soak in the water for 24 hours, but sometimes that plan doesn't work out. (I have a full-time job, so they might end up soaking for 48 hours, or when I find time after work to put them in dirt.)

Fourth, after soaking in water, they should have swelled up, so they are put in planter pots. I like using 3" peat pots because none of these trees are staying in my yard; they are all going somewhere else for their permanent homes. Using 3" peat pots gives them a good start and are inexpensive.

New sprouts poke above the ground in about a week.

In the photo below:
i) the tree on the left is from a batch planted June 4, poked above ground June 12;
ii) the tree on the right is from a batch planted May 9, poked above the ground May 14.
Today is June 20, so that is about 1 week and 5 weeks of growth.

In the June batch, 8 out of 11 seeds sprouted, which is a pretty good rate.

One more thing: I don't throw out the peat pots in which a Black Locust did not sprout.
I've read that Black Locust seeds can remain viable for many years. Just because a seed doesn't sprout now, doesn't mean it's bad. (Maybe I didn't scarify it enough. Or maybe it needs to go through a couple more winters.) In any case, I plant the peat pot somewhere I'd like a Black Locust tree to be and hope for the best. I may be surprised in a future year.

I've had pretty good luck getting robinia seeds to swell just by soaking them. I put hot water over them (I didn't dare to use really boiling hot water) and leave them in a cup. I changed the water every day or two, and took out the swollen ones and planted them in a nursery bed. If there's a robinia tree around that you can collect seeds under (like I did) then you'll have so many seeds it doesn't matter what the germination rate is. Anyway, I got several tiny little trees the first year, planted two out the next spring, and they barely grew that summer. But then this past spring there was no sign of them.

Meanwhile, recently a plant expert about my region went on a rant about what a harmful invasive they are here, and if anyone sees one they should cut it down and build a bonfire on the stump.... so now though I've still got another one in the nursery bed, I'm having second thoughts. It would mainly be for shade and greenery and maybe fuel if I decide my solar house isn't good enough, so really why do I need black locust trees?

About scarifying, I found a great tip on this forum. If you want to scarify seeds that are big enough, try using a nail clipper and carefully nip one edge of the seed, trying to get through the seed coat without biting into the material within. I've found it works pretty well.

Two weeks and no sign of a locust seedling, darn it.