As I write at the end of March, we are all restricted to
staying home, so those of us with gardens can be grateful that we have an
opportunity to be outdoors as well as something to keep us busy. Growing your
own food is even more important now.
Here in the Highlands, we have had some beautiful sunny days
but they come with frosty nights (it was -6°C last week) so I am not planting
anything outdoors just yet. However, the
weeds don’t seem to mind the temperatures so I thought I would focus on a
small weed that pops up everywhere in my garden, and probably in yours as well
– Hairy Bittercress (Cardamine hirsuta).
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| Hairy Bittercress |
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| Hairy Bittercress leaves with tiny hairs |
What does it look like? It starts as a small rosette of leaves
and then throws up a stalk a few centimetres high with tiny white flowers on
top. It is an annual and forms seeds in narrow pods which explode to scatter
the seeds far and wide. This explains its nickname of Popping Cress. It is part
of the Brassica family of plants so is related to the cabbages and broccoli.
All of this family have flowers with 4 petals arranged in a cross, hence the
other family name of Cruciferae.
You may never have heard of it but it has been studied
intensively. Its genome has been sequenced to help understand which genes control leaf formation . The popping seed pods have been researched as well. The explosive shatter of the
pods is so fast – an acceleration from 0 to 10 metres per second in about half
a millisecond – that advanced high-speed cameras are required to see it. To put
that acceleration in context, if it continued for a whole second, the seeds
would be travelling at 10 km/s or 3600 km per hour! A mighty effort from a tiny
plant. Here is the video.
You can understand why it can seed itself all over the
garden. The secret to control is to remove the plants before the pods have a
chance to split – and they don’t have to be dry to explode, so the sooner the
better. However, maybe you might find
the plant interesting enough to let a few grow to maturity and see it for
yourself!
There is another very similar plant called Wavy Bittercress
(Cardamine flexuosa). It is difficult
to tell them apart until they flower, and even then you have to look very
closely (a hand lens helps) to tell them apart. Hairy Bittercress has 4 stamens
whereas Wavy Bittercress has 6 stamens. Wavy Bittercress has a wavy stem and prefers damper ground.
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| Wavy Bittercress |
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| Wavy Bittercress (left) and Hairy Bittercress (right) |
Links
Scientists discover how a common garden weed expels its seeds at record speeds
Update - found a video on identifying Bittercresses, including some I did not know!
Update - found a video on identifying Bittercresses, including some I did not know!
