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Re: broad bean pollination

Allan Day wrote:
> 
> I am growing broad beans in a polytunnel and am trying to
> get the winter sowings to pollinate.  Does anybody out there
> know what would set the seeds in the winter months? We have had
> flowers since Christmas but none have set. Location is South
> Wales, UK.
Allan,

It's been my experience that broad beans (we call them fava beans in the
U.S.) continue to produce flowers until the soil dries out.  Of course
the stalk evenually gets too tall to stand up on its own.  It sounds
like you may have planted yours a little early if you've had flowers
since Christmas.

My climate is quite similar to that of Wales.  I usually plant no
earlier than Sept 1 and the end of October is still not too late.  The
plants grow all winter and by this time of year (mid-March) they are a
mass of stocky, healthy plants that completely cover the garden about
25-30 cm (1 foot) deep.  (I should point out that I grow them almost
exclusively for green manure.)  Very soon now they will shoot up and
start to flower.

The plants are somewhat self-fertile in that each flower will form a
seed pod from its own pollen.  But the temperature must be high enough
and each flower must be "tripped", that is mechanically opened, to
effect pollination.  Rain, hail and wind can trip a flower, but it's
extremely erratic and inconsistent.  Big pollinating insects are the
best.  You have also probably not had warm enough weather for pods to
set.

But all plants do better with cross-pollination.  Self-fertility is a
last-resort survival mechanism.  In my area most of the broad bean
pollination is accomplished by bumble bees.  They are strong enough to
open the flower and trip it, and they also carry pollen from one flower
to another so that cross-pollination is accomplished.  I have seen my
first bumble queens this week -- as soon as your weather settles a bit
you should see bumble bees on your broad beans.  (I *think* there are
native bumble bees in Britian???)  

Next year plant your broad beans in Sept-Oct and you should have mature
green seeds in May or June and dried seeds in August.

Steve  (Maritime...)
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