No, I didn’t know what ‘seed stratification’ was until last Sunday. James turned up with pots of germinated seed of yellow rattle (Rhinanthus minor). These had been in his fridge. How very counter-intuitive! I am constantly trying to find warm window sills to get seeds to germinate but apparently ‘stratification’ by placing seeds in a very cold environment is the way to go with some types of cold climate seed.
The idea is that you trick the seed into believing it has already experienced winter and is now ready to power out into spring. Cold climate plants cannot afford for seeds to germinate in the warm temperatures of late summer as the resulting plants might not survive long enough – due to winter frosts – to set seed themselves and continue nature’s cycle.
So the nearest thing to a ‘calendar’ to tell them when to germinate is temperature sensitivity; they won’t germinate until after a period of cold followed by warmth. Placing the seeds in the fridge aims to speed up the ‘cold’ period, and sure enough, the yellow rattle seeds had sprouted.
There was another pot with germinated seeds in flour and water … We’ve planted both lots experimentally in two small rows among some of our other wildflower plantings. It’ll be interesting to see whether they are able to withstand the often harsh conditions of Brighton Greenway (principally the competition of dock, thistles and nettles due to over-rich soil, and disturbance by dogs).
Yellow rattle is a particularly useful wildflower. It is semi-parasitic feeding off the nutrients in the roots of grasses. In this way, it helps control the growth of grass that we don’t want in our ‘wildflower meadow’, leaving the way clear for the less brutish wildflowers to thrive. It’s an annual but its rattling seeds spread easily and should germinate easily (even without being placed in a fridge) thus establishing the plant in our wildflower area and hopefully, helping other wildflowers to thrive.
There was a lot of evidence this weekend of wildflowers coming up strongly: achillea, centaurea, campions, herb robert … It felt counter-intuitive again to cut back this growth but that is what needed to be done in order to weaken the competitors. We’ve cut back strongly along the Isetta strip where – despite our best efforts – a set of ‘specimen beds’ respectively of nettles, dock, thistles and grass seem to have established. Underneath there somewhere our wildflower seeds are trying their best to come up. Again counter-intuitively, it is the nutrient-richness of the soil on the Greenway that is enabling this growth of the plant ‘thugs’ (alternatively, plants super-well-adapted to their environment). Hence the value of seeding yellow rattle …