I have read numerous articles regarding the use of lights for germination. Some have lights 16 hours a day over their seed trays starting when they were sowed, some don’t use any until they see some cotyledons, while others keep them in the dark until they transplant. I have had very limited germination from seeds that were still in the cold stratification, but much better once taken out and planted. I have not used lights right after planting, but was wondering if it would improve the germination rate?
I believe Henry’s website states that the red end of the light spectrum helps germination of seeds. So I would guess that planting them out would help. But I personally do not have the room so I plant them as they begin to sprout individually. If I had the room I would certainly plant all the seeds.
I think there’s very little evidence of light effects on roses. I have tried a comparison of light vs dark in warm conditions and found no difference but almost no germination either. For the many kinds of roses that I work with, some cold time is obligatory to get a decent percentage germination. Back in the '60s Peter Semeniuk and colleagues showed that continuous cold delays germination by as much as two months compared to fixed timed of cold followed by transfer to warm conditions. So just keeping them in the frig will slow things down. All the rest of the germination literature is “available” at the RHA website in my review. I don’t recall much positive results with specific kinds of light. It’s hard to do lighting without temperature change. There are seeds for which light is important, those that are buried in a seed bank in soil. Some weeds can rest there for decades until they get a light signal indicating they are close to the surface. Most roses are obviously not like that. They seem to sprout in total darkness. I can’t rule out the possibility that my checking on them every two weeks gives enough light exposure to trigger them. But I don’t think it’s real likely.
With nitrate added I’ve been getting upwards of 60-70 % germination in continuous cold after 4-6 months. So I already have around 1000 seedlings because some hips were ripe, ready to go to stratification in early August.
My most recent working hypothesis is that the old (1930s) studies of direct planting where it worked well depended on a combination of rich soil (nitrate) and cool nights during a Mediterranean winter (think Riviera). If you check the average temperatures during the winter months they were not much above 5 C (in the soil 1-2 cm deep) according to records I could access. Pierre could give us better data on how it is today…
My article based on a reviewed published Japanese scientific paper is at:
http://home.roadrunner.com/~kuska/redlight.htm
The general scientific literature covering Light and Phytochrome Involvement in Seed Germination can be looked at with a Google Scholar search
Thanks Henry for the link. Sure looks like it is worth a try to put some red colored transparent material on the trays. It is always good if we can do a bit of what Mother Nature does.
Hi Larry,
You have probably already reported this somewhere (so I apologize if that is so), but if you watered seeds that had been planted directly where they would sprout and grow, do you think that a drench watering of a nitrate solution would be beneficial and if so, what would you recommend as a mix per gallon of water?
This is fairly unscientific, but last year I watered half of any seedlings of which I had multiple flats with a nitrate solution and the other half with plain water. I didn’t notice any significant difference. It might be that the concentration would have to be increased when the seeds are in a growing medium.
Actually I’ve never done an in situ drench with nitrate. It only dawned on me, (or maybe the red light went on) recently. It will depend on how moist your soil is at the time. Assuming it is pretty much dry potting soil, a soaking dose of Hoagland’s solution would get you to about the right level.
I have done enough tests to know that the macronutrients in H soln are not important, or helpful, except for perhaps the potassium nitrate. So focus on the calcium nitrate that H soln uses. I went through the arithmetic and it works out very close to a final concentration of 1 g/L of anhydrous calcium dinitrate. So if you have a hydrated crystal form, or the ammonium double salt, you need to figure on a bit more. That will vary depending where you bought your stuff. Also if you kept it in a moist climate it takes up water. Probably in your town that’s not an issue. So about 5 g/gallon is a best guess, allowing for some water of hydration.
I hesitate to convert weight into dry volume. You wouldn’t be far off if you used one oz/5 gal of water if watering on a bedwide scale. An ordinary kitchen scale is quite good enough for that. Ours will even weight 5 g pretty reliably. (I know you have an M.D. so you know all this metric stuff but I’m wanting to include others too.)
Because the final concentration of nitrate is only that of 1x H soln, this isn’t going to hurt anything. We grow seedlings of all kinds of plants in this though often we use 1/2 x rather than 1 x. But you will be putting into a soil that isn’t completely dry so there will be some dilution.
I would only drench once with this, then water with good quality water to less than run-off. If you have high salts water you may need to flush the beds from time to time and then repeat the nitrate dosing. But at some point you will probably need to add other nutrients if you have to do a lot of flushing to prevent salt build-up. Usually the salts in irrigation (or city tap) water are not the balance best for plants. That’s another whole story. But it might be worth taking a look at the paper your city water supply sends out once a year to see how high the concentrations of various things are in the water you use. Any place that gets Colorado river water for instance has issues this way. Cities vary in how much they clean it up.
Hope this is more than you want to know.
Thank you Larry! What I may end up doing next year is to use a spray solution on the seeds when they are stratifying in the refrigerator.
I was not very scientific about it but I did do my initial soak of seeds before stratification with nitrate solution. It seems like I have gotten better germination this year. Should have done a control.
This is not about light so much as it is what I have done to a couple of crosses which I had stratified, applied the nitrate solution to and then returned it to the fridge like last yr. Since I have a few more seeds than last yr and they seem to be germinating better, I took out the two largest pacs and planted them when it looked like I was running out of flats again. This past week they started sprouting and I should have used a bigger box. I used the Costco loose leaf baby lettuce plastic container, about 6" X 10" X 3 or 4" deep, and planted rows every 3/4", spacing about 1", and then I ran out of room so I dumped the rest of the seeds on top with the nitrate treated vermiculite and roughly brushed that across them. yesterday I counted 68 seedlings in one box and 76 in the other. I had 180 seeds of the one cross, and 150 seeds in the other cross, and there are quite a few more seeds breaking the ‘soil’. If I directly sowed I would add the nitrate to the seeds about 3 weeks prior to the end of stratification, return them to the fridge for those three or maybe four weeks, and then sow. I have several (maybe 5-6 baggies) of 100% germination this yr so far, which may or may not be due to the nitrate, but with the speed of germination, and the high percentages of germ., I do not think I would ever try going back to ‘pre-nitrate’ germination. I will use this entry to make a note about one question I posed to Larry last yr about using the nitrate. I had a couple of browned out seedlings that appeared to be new germinations that had rotted, and I wondered if the nitrate could have anything to do with this. This year I figured out what the culprit is, and caught it in the act. In the afternoon I get about 15-20 minutes of tiny sun beams down right next to where I keep my seeds on the covered patio, and when we have a really hot Jan day like a couple last week, that sun apparently finds a space though the two big trees that block it mostly out and did a really good fry job through the clear plastic container and the plastic snack size baggies. It fried about 50-60 seedlings this yr. in the baggies, most nothing to get upset over, but 3 or 4 of them I was really waiting and rooting for.