Does a seed "know" the time of year?

If a seed germinates in spring, but the conditions are artificially reproduced, can the seed be forced to germination? Or, as with an animal that gestates at a particular time of year, does theseed somehow know that it is December, and not April?

 

It all comes down to chemisry I think. There are chemicals in the outer shell of the seed that react to heat and/or light and water and give the signal to germinate. So if you recreate the conditions thus inducing the chemical reaction that would occur naturally in spring, it will germinate I reckon.

 

Different seeds react to all sorts of stimuli which initiates germination, temperature, both cold and warmth, lenght of cold period, moisture, light, even things like smoke particles.

Gardeners use these stuimuli all the time to get seeds to germinate at the 'wrong time'. The most usual way is called stratification, where seeds of things that need a cold spell for a certain lenght of time can be put in the fridge, 'fooling' the seeds into thinking that winter has finished, and spring has started, the benifits of this is that all the seeds in a batch will start germinating at the same time, or earlier in the year, thereby extending the first growing season.

In certain weather conditions, seeds might be stimulated into germinating at the wrong time, but often these will be killed of by not having optimum conditions.

 

Thanks. The point you make about using the fride to fool the seed - is this similar to how a seed's dormancy can be broken by being placed at lower temperatures? I'm a mite confused as to how a lower temperature would encourage germination, when suually the opposite is required - and also how being placed in the fridge would make the seed think winter was over. Do you mean once the seed is removed from the fridge it feels like spring has come?

 

Sometimes, the outer casing of the seed contains chemicals which form a very rigid bond at warmer temperatures, but break down when cold. A bit like when tender plants fall apart in the cold, or when parsnips sweeten after frost. Once such chemical has been broken down by the cold, another chemical which was previously locked up in the outer casing is now free to leak into the inside of the seed. Once the weather warms up again, that newly unlocked chemical reacts inside the seed and triggers germination.

 

I would agree with clueless. I believe that it is all down to chemistry. A seed is naturally primed to germinate, but needs moisture.

Some seeds will easily germinate with moisture, but they often need a reasonable high temperature that is associated with spring. Simply putting them in a heated propogator does the same thing.

Other seeds such as Lupins have a physical barrier in the form of a hard water-proof coating, which prevents moisture getting in. This barrier breaks down with time in the garden, but you need to chip off a bit of this coat to get it to germinate quickly.

Some seeds have waxy coatings, and soaking them in hot water or acetone will remove them.

Others have chemicals present in the coating and need special treatments such as stratification (cold treatment). And some even have the equivalent of three coatings, and need, say, stratification to remove the first coat, then a warm treatment to remove the second coat and then a further cold treatment to remove the third coat. In the wild they would need two winters before they would germinate. The cold treatment will break down chemicals that are inhibiting germination. But the seed need moisture as well as the cold to do this, which is why the innermost coating, of the seed with three coats, in not effected by the cold treatment until the outer layers have been removed and the moisture can get in.

 

Just to add a further complexity, I believe some seeds have an outer coating that is very hard and is not effected by environmental conditions. Instead they need to, erm, pass through a bird's digestive tract where the digestive juices break down the hard outer case, before the rest of the seed, which is indigestible to the bird, is deposited later several miles from the parent plant.

Its quite amazing how nature has evolved so many different ways of ensuring seeds get about a bit. I watched a program on telly a while ago where some plant or other in Africa actually depends on bush fires. Nothing you do will make its seeds germinate, unless you set them alight and burn them for hours. They've evolved to take advantage of the newly cleared land that has been cleared by the bush fire.

 

Not only birds Clueless. What about Civit Coffee. http://www.firebox.com/product/1077/Civet-Coffee-Kopi-Luwak

:D

 

An interesting thread:gnthb:

 

Irrespective of 'normal' conditions, man (and growers in particular), have been manipulating the germination, flowering and fruiting time of plants since 'way back when'; from when he discovered some seeds grew quickly after being burned and took up 'controlled' burning, through rice growing rice in man-made paddy fields to the walled garden, bell jar, glasshouse, heated propagator and the computer controlled, heat and humidity regulator which allows our supermarkets to sell 'English strawberries' ... in December.

 

Seeds dont always germinate as the temperature rises. Lettuce will stop germinating if the temperature is too high. A lot of primulas go into dormancy if the temperature goes above about 65 degrees F I think. Some are triggered by 40 degrees to grow.
It is chemical triggers. In the wild a lot of plants, particularly from the Mediterranean would perish if they germinated in the summer, so they are programmed to germinate in the cooler winter. There are some bulbs that after germination if the temperatures gets too high then the seed root shrivels. Allium christophii will actually germinate in the fridge but there is no point in doing it in summer unless you can provide it with light and refrigerated conditions.

 

Geoff - you are right. There is so much more that most of us don't know or understand. Which is why understanding where a plant comes from invariably helps to understand how to look after it.

For instance many Tulips come originally from the middle east - places like Iran. Consequently they go dormant in summer to avoid what they think is going to be an excessively hot and dry summer. When they get our cold and wet summer - they tend to rot. So lifting them and drying them over the summer just replicates what they would have experienced in their homeland.

 

As has been said, there are many tricks to breaking dormancy on various seeds from around the world.

In a good few cases seed sold by "reputable" suppliers are, (In my opinion) , actually dead when you buy them, but thats a different story.

The real problems actually start, once you have fooled the seed into germinating, at what is probably the wrong time of the year.
Growing on the seedlings at the wrong time is never easy without specialist equipment.

 

Not quite on the subject of seed germination, but that statement reminded me of something I read in a horticultural science book I have. It is fairly new and was apparently written by some professors or some such high profile rank.

The book goes into scientific detail some of which is way over my head, but every few pages I keep coming across phrases like "further research is needed to understand this mechanism" or "this has been observed but an explanation is as yet not forthcoming".

So it seems even the top scientists don't fully understand it all

 

I heard someone say that the more learned he became he became more aware of how much more he did not understand.