Silly question but a question is a question so, if rose hips were left over winter with viable seeds in them outside and harvested around now, do you think they would’ve started the stratification process while in hip? Or would that inhibit the process entirely?
Not a silly question, just hard to answer. Generally it seems that simply storing fresh hips in a refrigerator is not enough to make them think they have been stratified. But outdoors they are not at a constant 4 C. Depending where you live, they may have gone through multiple cycles of freeze and thaw, or been scarcely chilled to 4 C. I’ve had reasonable luck getting germination from overwintered seeds. They seemed to take similar time of keeping at 4 C before sprouting, as those harvested and put into strat condn immediately. Germ % was not as good, but that could be from actual frost damage, insect damage or just deeper dormancy. The tests I did along that line were mostly done years ago. Reviewing my review (see RHA homepage), I see that for Doubloons, storing from fall 1988 to April 1989 didn’t hurt germ %, or time. But in later years Silver Moon x Evergold, stored cold several months in 2004 gave very poor germ % (19) compared to good % previous year 2003(69%) [ not a controlled expt].
More recent studies have been reported in the RHA newsletter, but most of those deal with 10 mM calcium nitrate in the stratification medium, except in the early years of 2009-2010.I don’t have all that data in a handy place. Maybe when I retire I will consolidate it.
We’ve had multiple freeze and thaws 4-5c quite a few times in central WA, lower than that too, I was below freezing last night, should I just plant the seeds removed from hips that were left in them outside? Or should I refrigerate it as well to stratify in there on top of it?
Again, I don’t think there is any clear answer. If I had a hundred seeds, I’d plant half after cleaning them out of the hips, and put the other half into vermiculite moistened with calcium nitrate and keep in the fridge until they sprout. Of course that will/might cost you a couple months of potential growing time. But if the cold is needed it will (probably) get you the best possible germination. The nitrate, for most types of roses, shortens the strat time by a couple months over simple cold moist treatment. However, for some, it gives a near infinite improvement. Some types won’t sprout anything in a year at 4 C, whereas they sprout a good % with the nitrate. R. canina harvested at some stages of ripening behaves that way. For other types such as R rugosa, nitrate has no benefit and there is very quick germ in simple moist cold conditions, with no increase of total by nitrate.
Seeds stored dry in hip cold or on a shelf are another whole story that I haven’t had time to figure out yet. Some have fair to good viability after considerable time, like years.
Generally it seems that simply storing fresh hips in a refrigerator is not enough to make them think they have been stratified.
Stratification and germination seem to require different temperature regimes. One thing to try is to raise the temperature to between 48 and 54 degrees F and hold it there for a while to induce germination.
I have germination now from seed harvested a month or so ago. Night time temps are starting to dip below 59f this last week and a bit, theres some rain most days (possibly washing away any inhibitors). Hulthemia hybrids, rugosa hybrids, chinas, multiflora/polyantha, moderns, portlands, sweet briars, centifolia hybrids, germinations across almost everything. Only issues are with the pimp group but those seem to be a second season germination for most. I’m sure stratification would improve some things germination rate but I’m not finding it a requirement to end up with more seedlings than i can reasonably handle/accomodate. Stratification is probably something to select against in my climate since blooming of roses happens 10 or 11 months of the year.
Granted I live where snow or freezes aren’t a thing and in the southern hemisphere (ie its fall/autumn, not spring, young seedlings can survive winter no problem, summer though can be risky), mileage may vary. If not committed to the seed, experiment, everyones conditions vary.
The effects of temperature extremes are not always immediately apparent.
Maize Newsletter Issue 21 (1947)
Maize and Heat
D. F. Jones
Varieties of corn grown in the Northeast and in the Middle West at the same latitude are noticeably taller in the East. Several environmental conditions are involved in this growth difference, principally light intensity and temperature. Plants of many species, including maize, grown under tobacco shade cloth are significantly taller and broader in leaf than plants from the same lots of seed grown in full sunlight. Under the cloth shade the temperature is the same as outside but the humidity is higher and the light intensity is lower. The same effect is noticed in the field where short-stalked varieties of corn are grown in single rows between taller varieties. Where there is a wide alley between ranges the plants at the ends of the rows are shorter than those in the center of the rows, the plants graduating in height. Here humidity and temperature are the same but light intensity varies.
Some corn seedlings started in the greenhouse and set outdoors were shorter at maturity than plants from the same seed started outdoors. This indicated that temperature in the early stages of growth had an effect. To test this, seeds of a uniform, vigorous, first generation hybrid (Wf9 x P8) were germinated in an incubator at about 30° C. until the shoots and roots were from one fourth to one half inch long. Three different lots of sprouted seedlings were held at 40, 50 and 60° C. for one hour. They were then planted in pots and left in the greenhouse until it was certain the plants would grow. They were then set in the field alongside plants from the same lot of seed sown in the open ground at the same time the treated seedlings were started in the incubator. Some of the treated seedlings died but enough were started in each lot and later thinned to give an even stand of plants in the field.
All three lots of heat-treated seedlings were shorter in height, less vigorous in growth throughout the season and later in flowering than the treated plants. All lots grew to full maturity and were measured after growth had ceased. The results are: Control 101: 40° C. 87; 50° C. 89; 60° C. 93 inches in height. The differences between the three temperature treatments are small. All three averaged 90 compared to 101 inches in height for the control.
The result that was not anticipated was the pollen sterility in all treated lots. Normal tassels were produced with well-developed florets but the anthers were small and shriveled and for the most part remained enclosed in the glumes. In view of the fact that high temperatures sterilize the male germ cells in animals, from amphibians to mammals, these results are highly significant. This influence on growth is an anti-vernalization effect and may have wide usefulness in the production of hybrid seed especially if shown by other plants as well as maize.
And another odd case:
Plant Physiol. 1959 Nov; 34(6): 643-644.
EFFECT OF VERNALIZATION ON HEAT RESISTANCE IN TWO VARIETIES OF PEAS
H. R. HIGHKIN
The effect of a cold treatment on the response of pea plants to high temperature has been studied. It was found that there is a marked increase in heat resistance as a result of a cold treatment. The induction of heat resistance as a result of vernalization appears to be independent of the induction of the floral stimulus resulting from such a treatment.