Life in a Dol house
2018 - Week 16

Allelopathy and beneficent weeds

Break out the shorts! 

The day time temperature crept over +25ºC this week. 

Now of course in many other parts of the world, it has been over +25ºC too. 

Even London managed to break a record or two this week with its temperatures, but fear not Londoners, it will be back to normal for you next week - cool and wet! 

For the Mediterranean, ours is a more permanent temperature, at least until September.

After a very wet winter, with more than 550 litres, or half a tonne of rain per square metre, this week when I have continued to remove the weeds, the ground is parched and cracking and in places impossible to penetrate with a fork. 

Such is the nature of a clay soil, which dries and solidifies into large chunks. Dig down a little, and there is a small colouration to the soil, but no more than dampness, not what could be described at "moist".

​I've cleared the herb bed and have sown a number of different herbs in the greenhouse, actually each in their own individual greenhouse (those plastic boxes that things like croissant come in at the supermarket).

At the start of the week, as I was exploring under a weed to find its root, so I could remove it, what struck me was that NOTHING was growing. 

No grass, no seedlings, no other weeds. Nothing.

This prompted me to leave it. 

I have quite a lot of these particular weeds, in large dark green clumps, covered with yellow flowers, in parts of the citrus orchard.

They are highly attractive to bees, butterflies and other pollinators and exploring further, almost nothing was growing under any of them.

In just one or two places thistles had grown up through the weed canopy to reach the sunlight.

​Thistles have long tap roots of course, but these yellow flowered weeds have a network of fine roots which are very close to the surface.

I am aware of what is called Allelopathy, the ability of some plants and trees to inhibit or prevent the germination of seedlings within their vicinity, through the creation of natural biochemicals either in the soil, or in secretions from the leaves or branches. 

There is also what is called "resource competition", where quite simply they out compete other plants for light, water and nutrients and literally starve competition to death. 

Sumac, Golden Rod and Rhododendron are all examples of common Alleopathecic species. Rhododendron is classed as an invasive species in many parts of the world where it has been introduced to, and has escaped into the wild.

This however was just a "weed". 

Weeds are something I have a lot of, and something I have been fighting a war of attrition with, ever since I moved to my Dol house. 

Remember the definition of a 'weed' - when you pull everything up, what grows again is a weed!

An alternative and less banal definition, taken from "The Manual of Weeds", published in 1919, is "A weed is a plant that is growing where it is desired that something else shall grow. It follows that a plant may be a weed in some places and not in others".

​So throughout modern history, the botanists and plant hunters have been bringing "beautiful weeds" back from far flung forests, to their native countries and have then tried, coaxed, nurtured and nursed them, to get them to grow in places where neither the climate nor the conditions were conducive for their survival.

Plants like the lovely Bougainvillea, which in its native South America creates impenetrable jungle thickets of colourful vines, whose sharp thorns prevent predation by animals and man.

But after the French Admiral Louis Antoine de Bougainville's botanists team discovered it in 1789, and brought specimens back to Europe, where the conditions are OK, but not perfect, what could be described as a weed in one part of the world has become a desirable and sought after plant in another. 

People work extremely hard to persuade it to grow in places where it would not survive without the help of mankind.

Not every introduction has such a happy ending though. Some plants, for example, Japanese Knot Weed, Fallopia japonica, which has been carried way beyond it's original growing area, is now difficult to control and almost impossible to eradicate. 

I have an example of a different plant growing in my garden. The "Trumpet Vine", Campsis radicans, which has large orange flowers in the summer, but is an inveterate climber which throttles everything it climbs.

​It spreads under ground, it's roots breaking through concrete and dislodging dry stone walls. 

Although I have tried to eliminate it, I saw this week that there are some new shoots that have appeared! 

Not everything with a nice flower is welcomed by a gardener...

In botanical evolution, all plants, pretty, ugly, useful or useless have developed their own means of of survival. 

By definition, they are still here, so must have done something right. 

That might be transferring seeds to passing mammals, like the plant known in the UK as "Cleavers", Galium aparine, whose long trailing tentacles climb and twist around anything and everything, then as someone or something passes, its sticky seeds, known as "Burs" are transferred to drop or be knocked off elsewhere.

The the square stems attach themselves to anything which passes.

​The Hairy Bittercress, Cardamine hirsuta, whose long, thin explosive seed pods ensure that its seed is broadcast far and wide and of course the Thistle, Asteraceae and the Dandelion, Taraxacum, whose parachute seeds take off when ripe and are wind borne across the globe, have all developed effective mechanisms for survival, which horticulturalists work to defeat.

Each has a place, but in the wrong place is a weed - and I have all of these and a lot more I can identify as such, but cannot give name to.

Because weeds tend to be expert at spreading their progeny forth, my discovery of what this plant was doing to prevent others growing was of interest. 

Anything that will reduce the annual and continuing demand for weed removal is of interest to me. 

It is only a couple of weeks ago that I reported on a trial I am running with different plantings in the Drupe orchard, to see which will do just this for me, so discovering something 'au natural' is of great interest.

Out came my books to try and find what it was.

​You can upload a photograph to google to try and match, you can put the description into a plant hunter website, you can search through books, but sometimes they all draw a blank. 

So after going page by page through my various wild flower books, I had identified two pretty weeds I have, but not this one.

Next step was to consult knowledgeable friends, who in turn posed the question to others. 

It was Friday morning when I got the answer - it is Medicago falcata, also called Yellow Flowered Alfalfa.

​The shape of the flower I had recognised, but couldn't put a name to it. 

I described it being the shape of a Laburnum. I should have said "Sweet pea". It is a legume after all, although Laburnum is also a member of the same genus. 

The USDA have a data sheet on the plant, which is used as a forage crop. 

It was this that provided me with the information I really needed. 

It is indeed a beneficent weed, originating in the Mediterranean basin, it does not spread wildly, can be an annual or perennial, is drought tolerant and there are no environmental concerns about the plant. 

It does indeed inhibit the growth of other annual weeds and is not considered invasive.

So on that basis it can stay.

 I have been digging out the thistles and other deep rooted weeds where they are showing through and leaving the Medicago falcata alone. 

I hope it lives up to its reputation!.