BL 46 2012 - re late season for bulbs.

[tonyg]

Ian.  Another interesting log.  Your crocus are at very much the same stage as mine which were re-potted in the weeks after your visit here in early September.  Despite the lateness of my re-pot and later watering as a result, we seem to have our flowers equally late.  Why?  I wonder if the long cold spring (after the March heat) which kept plants in leaf for much longer than usual might be part of the reason.  As the leaves lasted longer I assume the roots were active late too.   Do the plants need a certain length of summer dormancy?  Maybe they do.
 
Pity about the low light and lack of insects which must be worse in the North.  Hopefully you have more time for hand pollinating than I do.

I am hoping the late start for the 'winter' narcissus means that they will flower after mid-winter, as the days lengthen and light intensity improves.  A late start might be better for them.  Mine are even less advanced than yours.

[David Shaw]

Unlike Ian, I have never seen so many hoverflies in our bulbhouse as during the past week. I do note that our crocus are very 'leggy' this year, presumably due to the lack of sunlight and the narcissus are miles behind those of Ian.

[Darren]

Personally I think (as a biologist) that summer dormancy requirements are likely to operate at least partially on a 'degree-days' principle rather than just timing. Kind of hard to explain but imagine 'adding up' the temperature readings over a period of time. Once a certain threshold total is reached then the bulb is able to respond to the growth stimuli again. So more days dormancy at cooler temps are needed than if temps are higher, in order to reach the same total of 'degree-days'.

This year, with a notably dull and cool summer, this threshold value may not have been reached until several weeks later than usual (not helped, as Tony says, by the late start to the dormant period). Most of my bulbs are up to a month later than usual with some (Massonia depressa) over two months late coming into growth. Those Cape species which sometimes take a 'year off' are doing so and I wonder if this is because in cool years the 'degree days' threshold is simply never reached and the bulbs have to wait until the next dormant period to complete the process?

For some species (I'm thinking of those Cape species which stay dormant for years if under the shade of fynbos shrubs) there is probably also a minimum highest temperature requirement which signals, either due to a bushfire or more sun reaching the soil, that the competition has disappeared and flowering can commence.

[Tony Willis]

Interesting comments on the lateness of the season as this is not my experience this year.

tonyG mentions the leaves lasting longer this year in the spring but not with me. During the one hot spell of the year in March I was freezing in rain and bitterly cold winds in Southern Spain and when I got back the top growth on my crocuses and a number of other species had been burnt off and the plants gone into early dormancy. We have had a cold summer with rain most days,although the bulbs are kept dry with very low average temperatures.

Looking at flowering times this autumn(I record the date on my photographs) there is very little difference in flowering times over several years and in fact some of the sternbergias flowered earlier in 2009.

[Gerry Webster]

My experience is of great variability. All were watered as usual at the beginning of Sept. Early sp. such as boryi & banaticus were very slightly later than usual & are long gone but later sp. such as longiflorus are in flower now - about 1 month later than usual. The summer here was very cold & wet.

[Darren]

Interesting comments on the lateness of the season as this is not my experience this year.

tonyG mentions the leaves lasting longer this year in the spring but not with me. During the one hot spell of the year in March I was freezing in rain and bitterly cold winds in Southern Spain and when I got back the top growth on my crocuses and a number of other species had been burnt off and the plants gone into early dormancy. We have had a cold summer with rain most days,although the bulbs are kept dry with very low average temperatures.

Looking at flowering times this autumn(I record the date on my photographs) there is very little difference in flowering times over several years and in fact some of the sternbergias flowered earlier in 2009.

Tony - perhaps your early dormancy might explain why yours are on schedule this autumn?

Variability between species is what you would expect as they will all differ in their dormancy length/temperature requirements. I would have expected that species from cooler/higher habitats would be less thrown by a cooler summer whereas lowland mediterranean or cape species might. In a warm summer all of them will have had their minimum 'degree-day' requirement met and therefore less variability would be evident in autumn as they should all be ready to respond rapidly to that first watering. (Incidentally- I believe the discredited old advice to 'give bulbs a summer baking' is no more wrong than the more modern 'bulbs don't like to be hot and dry'. Both these views are generalisations and don't take into account differences between species, even within a genus.)

In 2011 we had a very warm spell in spring so things died back earlier and I found that my bulbs started to regrow much earlier in the autumn too, and seemingly with more vigour, despite another poor summer (though better than this year!).

I intend to experiment with this next year - especially to see if I can avoid the 'year off' syndrome in some Cape bulbs. My intention is to split a potful of the worst culprits when they die back in spring. Treat one half as normal (ambient temps in the greenhouse) and keep the other lot several degrees warmer during summer in a propagator. Then put both halves next to each other back on the bench and water both in september as normal. Of course this assumes another cold summer....

I was chatting about this with David Boyd on monday, regarding his farrer-winning Nerine humilis and he believes as I do - that timing of growth/flowering in autumn is related to summer temps during dormancy. His Nerine is, like my sarniensis, a month later this year and is flowering with leaves already present too - whereas flowering normally pre-dates the foliage, which suggests to me that whatever temperature requirement is needed to trigger leaf growth is not necessarily coupled to that for inflorescence development, which again makes sense.

You can read more about accumulated degree-days here:

http://www.ipm.ucdavis.edu/WEATHER/ddconcepts.html

[Tony Willis]

Darren mentions bulbs missing a year and so I will talk about Narcissus serotinus.

I got some bulbs in 2008 and they have made no growth in 09,10 or 11(roots or leaves) but have this year put up both leaves and flower buds. There were five flower stalks but three have now aborted. Given that both last summer and this one have been cold I can offer no explanation for this. A bulb I have given a fellow forum member in the midlands has still made no growth.

I kept them dry all summer and watered them on 1st September.

This coming summer I intend keeping them warm in the airing cupboard and trying to start them into growth in August. I feel that the buds have died because it is too cold now for them to develop.

[ian mcenery]

This is a very interesting topic. As I have only succumbed to growing bulbs in pots in the last few years any deficiencies I have experienced I have always put down to my poor cultivation and part of the long learning process so it comforting to know that others have had the same experience this autumn. My plants were slow into dormancy this year and probably as a consequence have been slow into growth.

I must say that Darren's theory of temperature days is very interesting and may be right on the money when it comes to South African bulbs.  However   such a theory doesn't explain why some crocus seem to appear in the north earlier than in the south. Perhaps there are other factors at work here which are dependant on lowering temperatures, amount of daylight and moisture to trigger growth. 

[ArnoldT]

I think temperature plays a role in initiation of growth.  I also think there are other factors at play here.  Before i had a greenhouse I kept a number Boophone disticha in a cool basement and without  any significant  change in temperature they showed growth right on schedule in March.   Colchicums   have been known to flower sitting on  shelf out of the weather.

[Darren]

This is a very interesting topic. As I have only succumbed to growing bulbs in pots in the last few years any deficiencies I have experienced I have always put down to my poor cultivation and part of the long learning process so it comforting to know that others have had the same experience this autumn. My plants were slow into dormancy this year and probably as a consequence have been slow into growth.

I must say that Darren's theory of temperature days is very interesting and may be right on the money when it comes to South African bulbs. However   such a theory doesn't explain why some crocus seem to appear in the north earlier than in the south. Perhaps there are other factors at work here which are dependant on lowering temperatures, amount of daylight and moisture to trigger growth. 

One might not think so...but. As I tried to say - what if bulbs needed to accumulate enough 'degree-days' to prime them before they could respond to normal growth stimuli such as water/cold in autumn? Given that it will likely get cold and/or wet earlier in the north than in the south it makes sense that the actual growth will begin earlier in the north if the bulbs are primed and ready after a decent summer rest. I would postulate that if we got a cold/wet spell in june (not unusual) it won't make your winter crocuses flower in july?

Thinking about it - if the 'degree-days' thing wasn't helping to maintain dormacy then you would see bulbs responding to unusually cold/wet spells in early summer by coming into growth at the 'wrong' time. As a rule this does not happen and it would be disastrous if it did because they would not be able to grow properly before being knocked back again by a subsequent two months of hot weather, so there must be a mechanism to 'time' when sufficient dormant time has gone by, and it is safe to start growing again.

Flowering in dry colchicum can still be explained the same way as (as noted in my comments about nerines) flowering triggers are not necessarily linked to growth triggers. Gethyllis and some other winter-growing amaryllids flower simultaneously in response (apparently) to passing cold fronts in late summer - long before the first rains trigger vegetative growth. It is thought possible this is linked to sensing of cold or of barometric pressure. But I still feel it likely that a certain number of warm days must pass before a cold front triggers a response (i.e. the flowering mechanism is then 'primed' and ready to respond.

I think that summer growing bulbs such must obviously have different triggers but may still in some way have a 'degree-days' requirement, but switched round the other way. Perhaps sufficient cool time needs to accumulate, in the same way a certain amount of cold period is necessary before some seeds will germinate? This is possibly less fixed as we all know some will often start growing in winter during a mild spell.

Tony - I can't explain the discrepancy between your plants and those in the midlands but if the 'degree-days' thing is truly cumulative then perhaps your Narcissus have accumulated enough over 3 seasons to allow the to respond and grow this year? In the wild, or a decent summer under glass they would accumulate enough 'temperature loyalty points' in one season.

It (the degree-day thing) isn't my theory but an established biological phenomenon which, I think, makes sense in this context.

[ArnoldT]

A very interesting topic indeed.

In Physiology of Flowering Bulbs, 1993  edited by August De Hertough and Marcel Le Nard there is a discussion of this subject.

The chapter ends with:

To conclude, our knowledge of the fundamental processes of growth and its inhibition and periodicity and dormancy in bulbs is rather limited.  Only a few fundamental studies on dormancy are available( see chapters Part B). A better understanding of these processes needs to be obtained if optimal control of bulbs growth and development is to be achieved.

[tonyg]

Darren.  Thanks for such a comprehensive explanation.  I think the Degree Days theory fits with my initial, rather vague exploration of the issue.

[Ian Y]

Just back and catching up on this thread.

Darren's comments are broadly similar to temperature gradient being the trigger.

The factor that upset some of my thoughts was how quickly bulbs sent from the Southern Hemisphere came out of dormancy, flowering out of season, having a brief second dormancy an starting back into growth for a third time inside twelve months.

There is obviously more going on than we think and as has been suggested the triggers are complex an may involve several parameters.
My other observation is that it is the autumn flowering bulbs that have a more complex triggering system.

Spring flowering forms have a requirement for a cold period before flowering is triggered and it is easier to control their flowering time as we can see from  the mass displays of early spring bulbs in flower at Chelsea towards the end of may.

[ArnoldT]

I would think that there are more than one trigger and it takes two or three trigger to initiate growth.

This would prevent a bulb from coming into growth with just a unusual warm spell of an out of sorts rain storm.

[gote]

 We do have a lot of data on dormancy etc - on seeds. I think that many of us have found that seed germinate at the time of the year when the adult plant starts into growth. This is of course natural since both need to start at the same time of the season. Deno's reports might be helpful in hinting the best way to start bulbs into growth.
My own most striking experience is from Acidanthera muriele/Gladiolus callianthus. I usually get fat bulbs in the fall and I used to store them the way everybody adviced i.e. cool and dry - they usually did not grow a second season. I noticed that rice grains that I had dropped on the soil sprouted in August - far too late. The previous winter I stored them in a paper bag in a place that varied between 20 and 23°C. Planted in the spring, they sprouted within a week. I had a mean of three spikes for each bulb.
Happy New Year! everybody
Göte