Hairy bittercress and thale cress, ubiquitous garden weeds
|If you don’t know what bittercress looks like you will soon if you read further|
|And if you read to the end you will know about thale cress|
Hairy bittercress is that wretched small weed which appears in late Winter before inexperienced gardeners even think about weeding. It germinates in empty spaces and soon starts fizzing out seed all over your previously immaculate garden. Described as ephemeral, continued short generations bedevil you for the rest of the year. Unless you are alert to its rapid reseeding after as little as a month following emergence you will never be rid of it.
Rare as a weed when I was a child, it is a modern phenomenon. (Considering my age, not that modern). As a common weed it has been encouraged by modernity and has been a product of the expanding garden centre industry over the last sixty years. How often has it lurked at the top of the pot of your new plant? Almost always!
Bittercress is the curse of the nurseryman. He has historically controlled weed in containers by using sterile or sterilised compost. He also uses residual herbicides to prevent germination of weeds that have blown in. Bittercress rapidly establishes on the otherwise clean standing ground for container grown plants. With its ‘exploding’ mechanical dispersal - known to the botanist as ballistic dispersal, bittercress seed is thrown in the air and is flung as far as a meter and straight into plant containers. It’s sticky seed coat helps it hold on.
|My friend Peter Williams once studied the mechanical distribution of bittercress and how far it would jump!|
Over the years bittercress has proved to be resistant to the nurseryman’s residual herbicides. The only one that actually worked was withdrawn because of licensing costs.
(Residual herbicides have never caught on with amateur gardeners - other than as an ingredient in path weedkillers - but are widely used by farmers and growers)
And of course bittercress has been distributed to garden centres far and wide.
Description and identification
|An extreme variation. This bittercress is very low growing and is rife in extremely wet conditions.|
You will have no difficulty in identifying all of them as hairy bittercress when they take over your garden. Superficially they do not seem very hairy to me. Leaves are actually quite smooth. The larger strains (or possibly just the more luxuriant specimens) make quite delicious salad and are not really bitter at all. Shame about the inevitable mouthful of soil.
With difficulty! The actual killing is easy - its the timing and access that makes it difficult.
If you have got a clear run in more open spaces 1in 50 commercial strength glyphosate will surely kill it it. Unfortunately in the days it takes to die if it has started to seed it will continue to spit out more seeds to start all over again. Dare I say it, perhaps speedy diquat containing amateur products are better? (I do not personally use or advocate unsafe professional liquid-concentrate formulations of diquat for gardeners)
|The only way to control this bittercress and keep the self sown nigella is to pull it out|
Hand weeding is fiddly, takes a long time and is often too late to prevent seeding. It is actually quite difficult to pull out when very small. I frequently break the seedlings’ necks by sliding my foot over them.
|But his former student Julie is a beautiful weeder|
|This shrivelled bittercress will not recover|
Unfortunately the weather patterns this year for me have been particularly conducive to bittercress and I have never had more!
My own control policy is if I see a bittercress seeding - which is most of its life - I kill it on sight. I bend my back and pull or scrape it bootwise or grab my hoe or point my spray. It must not seed! But oh dear how this year I have failed.
Many gardeners ask me how to control this weed when it is propelling its seed all over their borders. Sorry it’s too late.
The only way is constance vigilance, stop it seeding and get it out of the system. You might be in full control in a couple of years. That is if you don’t dig buried seed to the surface - although I must admit it likes the settled soil surfaces typical of non diggers like me!
I know of one gardener who advocates very deep mulching to control weed from seed. If you have a clean start with no bittercress seeds popping and are perhaps prepared to cover the contaminated soil three inches deep (phew) I think this will work. Beware any aerial bombardment however. Nothing likes an organic mulch as a seedbed more than newly scattered hairy bittercress.
Hairy bittercress in pictures
|Can you spot it?|
|Dwarf form carefully weeded|
|How did I miss these two|
|You might find it in low quality lawns|
|Sprayed in seconds - it's all weed|
|The dwarf form is quite sneaky - and at first pretty|
|It's lost a petal - there is always four|
|Littles and large|
|Not all cardamines are weeds, some are very select garden plants|
|Dwarf form sets seed|
|Leaves are distinct, flowers are held higher, it looks more delicate and I don't think it goes pop|
It does not disperse its seed with the same vigour as bittercress but if does seem to set seed even quicker - I can scarcely believe this is possible. I was shocked in Peter’s garden today how tiny his flowering thale cress in his dry border could be. I have spent all Summer trying to see if thale-cress forcefully disperses its seed but it does not go pop for me.
|Thale cress is really quite delicate and is very quick to set seed|
|Three ' weeds' in a row - thale cress, honesty and Dicentra cucullaria.|
(My next post is about variegated honesty)
More is known about the genetics of thale cress than perhaps any other plant. It is the darling of researchers. They love getting speedy results from its very short life cycle!
A fairly 'heavy' link to US research on bittercress
I have written about several weeds now. Look for your problem weed in my search box!