Rumble In My Jungle - The Allelopath Wars

Chemical warfare isn't an invention of mankind. Long before mustard gas, plants were merrily dosing one another with foul concoctions designed to maim and kill. These chemicals are known in science as Allelopaths.

Allelopaths are chemicals used by plants to damage one another and are administered by different methods which include diffusion in the air from leaves, flowers or stems, soakage into the soil via root systems and distribution through fallen leaves.

It seems one of the most effective users of this chemical warfare is the black walnut tree which owners will observe, creates a protective blank space of earth around it in which few other plants can live. Other noted allelopathic killers include hackberry, garlic, eucalyptus and black cherry.

When Garlic Sprouts Attack ...."AAAAGHHH!" 

The effects of destructive allelopaths include hindering growth or preventing it altogether by issuing chemicals which prevent rival seeds from germinating.

But plants don't only seek to eliminate or limit their competitors with chemicals. Some use chemicals to encourage other mutually beneficial species which don't provide a threat - and indeed may help their cause attracting the right insects for pollination and so on.

Food gardeners have known about the effects of allelopaths for thousands of years and employ them constructively in what we commonly call "companion planting" today. For example gardeners know that garlic is destructive against peas, cabbage and beans but helpful in keeping pests away from carrots or tomatoes. Peas and beans, who both pursue the same nutrients in the soil, actively combat one another, as do lettuces and parsley.

"Three sisters" planting in my garden - squashes, beans and corn helping one another.

The central american native peoples used beneficial planting to increase the crop potential of beans, corn and squashes. The "three sisters" method they deployed also produced physical benefits for the crops in question. The beans used the stout corn stalks as beanpoles to climb on to get vital sunlight and with their flowers, helped attract pollinating insects for the corn. 

The hungry ground ranging squashes were fed by the nitrogen gathered and locked into the soil gathered by the beans and in turn would provide a natural ground cover to prevent the soil drying out under the sun while the spines on its stalks and foliage would limit pests. All three plants helped one another. It would be common sense to assume that their chemical allelopaths also aided the process.

But of course, it is the destructive aspects of allelopaths that attracted my interest...

So, in the interests of science you understand....I decided to pitch some allelopathic heavyweights against one another in my garden to see what the outcome would be..

BOUT ONE - TOMATO V FOXGLOVE

Tomato - sweet to eat but the deadly nightshade's relative has foliage brimful of deadly solanine

In the red corner: The tomato plant - Solano lypopersicon. Often attacked by fungi in a damp climate like Ireland's but never by insects. Known natural toxin arsenal includes solanine - known to kill pet dogs. 

In the blue corner: The hardy nasty native - the Foxglove - Digitalis pupurea L. - living in Irish woodlands for tens of thousands of years, spectacular orchid like blooms and big thick heavily wrinkled foliage - almost never nibbled. Toxic. Natural toxic arsenal includes a chemical commonly used in a last ditch attempt to stimulate the human heart  - causing it to spasm - or go into shock. Interestingly however French gardeners have long let Foxglove free seed among their vegetables and salads because they believe it causes stronger growth and builds up disease resistance. This plant operates with a big allelopathic punch.

I stuck a juvenile of each of them in one planter and stood back to watch the show. Surely a bout of floratic chemical wrestling to beat all?

Foxgloves (left) meet tomatoes (right) in a fight to the finish

I had often planted tomatoes in containers already crowded with low ranging plants - and with great success, so I knew tomatoes can live in close proximity with myriad species.  Nearby I planted the same size tomato plants (about a foot high)  in other containers and on their own. There were also other foxgloves alongside in their own containers - both sets of solitary plants would provide a control by which to measure the effects on the two plants of different species which would be forced to share a container. 


The results were astounding.

Within two months the foxglove's growth was impaired by about 25pc compared to the other non container sharing foxgloves. However the one sharing with the tomato was the only foxglove of all of them all to go into bloom - perhaps feeling an urgency to do so. On the other hand, the young tomato plant sharing a root system with the foxglove, lost leaves and did not gain any growth at all. The remaining leaves turned from green to purple. In contrast, the other tomatoes in adjoining containers pursued their normal growth patterns.

Foxglove 1 Tomato 0.

Puree-ed!

In the raised beds I witnessed another non intentional allelopathic war. 

 BOUT TWO - MINER'S LETTUCE V BUTTERCUP

In the red corner - miner's lettuce is a voracious north american ground hugging plant with succulent like leaves. It was named for the great gold rush during which miner's caught in snow bound conditions often survived using it as a food. Over a number of years the plant had spread far and wide in the raised beds and was now out of control. So dense is its growth that it would be difficult to see how any plant could compete with it.

Miner's lettuce starting to spread - you can see the buttercup starting in the right hand middle left of the pic 

In the blue corner - buttercup. I had last year distributed new topsoil around the garden which wasn't as sterile as it could have been. There were buttercup, nettle and dock seeds in it which began to sprout throughout my garden. Next to the miner's lettuce, a ground crawling buttercup surfaced. It's a plant known to be highly toxic. This would be an interesting battle.

It would end up being a knock out. Within just weeks the buttercup was dominant and the miner's lettuce had been completely eradicated.

Buttercup 1 Miner's Lettuce 0.

Now the buttercup has moved over to impinge on the territory of a very vibrant and pungent crop of sage. I'm already selling tickets.

In the same spot weeks later... the miner is shafted and the buttercup squares up to the great sage..

Science is still in the early stages of studying allelopaths which may in the end provide us with beneficial eco weedkillers as we harvest and use some of these plant chemical weapons against weeds. 

Five to four on buttercup anyone?

Why My Dad Can't Have A Flamethrower (and the Plot 34 Guide to Weeds)

I thought I’d heard him right. “You want to buy a what?” I did hear him right!!

What do you do dear reader if your pension age dad -  master of showing up with cuts, grazes and fingers like an elastoplast mummy - announces that he’s going to buy a flame thrower? This is the man who once set the chimney ablaze by cutting off bits of his Christmas tree and feeding it into the livingroom fire - seceteured electric fairy light segments and all. Only my dad could set his chimney alight thus threatening an all out housefire while simultaneously risking electrocution.

We got onto the subject of flamethrowers by way of a discussion about chainsaws - of which he has two (this one's electric, that one's petrol)  despite living in a terrace house with a rather small garden and little about to chainsaw. He likes his dangerous gadgets does my dad. Woe betide anyone who breaks into his house. Especially now that he’s in the market for a flamethrower. They must be selling them at Lidl.
-“What the hell do you want a flamethrower for?!“
-“To burn off weeds.”
“-You’re not having a flame thrower!”
-“Ha ha! Yes I am.”

Would you let this man have a flame thrower?

A weed burner would be a more correct description. However a weed burner is indeed a faithful reproduction in miniature of the very same notorious device once deployed by marines to toast stubborn hole hugging Hirohito-ites in the Pacific.

But the trouble with a retired man of a certain age having a flame thrower at hand is that he’s likely to start trying it out for uses other than that which is proscribed. Perhaps he’ll have a go at a wasps nest with it, or go after mice. He also needs to know that while a weed burner is a more eco friendly way of going after weeds on footpaths and walking areas than toxic chemicals, they should not be used on growing soil because they also kill the organisms which help it do its thing.

Flamethrowers - not suited for garden work

For much of the year, weeding is one of the home food grower’s main duties. Inevitably they grow faster than your crops especially if the crops happen to be carrots. Carrot growers in particular will find that because of the need for a finer tilled soil, their neat lines of seedlings soon disappear amongst a amongst a forest which appears to include every specimen in the book. I spent an hour picking my way through one carrot bed last year, removing the tallest weeds first, chickweed last, before finally determining that there weren’t actually any carrots left in there at all.

A weed burner as bought on Amazon - not the same thing

By way of making weeding easier and by way of giving the amateur grower a grounding in identification of what others fondly term “wild flowers,” every year in July, at the peak of the weed season, the Organic Centre in Rosniver, County Leitrim offers a course a course in weed identification and study given by leading horticulturalist Ingrid Foley. To give us a taster of what my dad might be applying his flamethrower to,  I’ve asked her to give the low down on fsome of the most stubborn specimens out there.

Really Digging the weeds - that's Ingrid on the right (Sligo IT)

“While we might hate weeds, they absolutely love us,” says Foley. Experts believe that some weeds have actually evolved ways of getting humans to help in their regeneration. “Weeds employ a number of devious and clever devices to harness people and animals in order to reproduce.”

And this is what you need a flamethrower for because bittercress sets its very own IEDs. Brush past a ripe bittercress and it literally explodes, hurtling hundreds of tiny seeds all over your plot. Other ingenious weeds include the ubiquitous Cleavers, otherwise known as Galium Aparine, or more popularly here in Ireland as the “stickyback.” This hitches a lift on humans or animals in order to spread its seeds. The plant is covered in microscopic hooks which fasten to our clothes, break loose and “hitch” until the hooks slacken and the seeds/segments drop off elsewhere. Other plants like the Red Dead Nettle trick insects into carrying their seeds away.

“Then there’s the airborne invaders like dandelion and thistles which generate seedheads made up of hundreds of tiny parachutes enabling them to glide off to new ground.” Finally let's not forget the sneaky “creepers” in the long grass which send out “runners” that can span across  a vegetable bed within a few short weeks.

So in the interests of providing humanity with the necessary intelligence to claw back some growing ground from the dastardly ones - here's Ingrid's field combat guide to warfare with the garden baddies:

Chickweed
Thus called because we feed it to chickens. We can also feed it to ourselves because it’s edible for humans and contains a remarkably high amount of nutrients and minerals including potassium, riboflavins, magnesium, beta carotene and it’s especially high in iron. Unfortunately that’s because it’s depleting all this good stuff directly from your soil.

Light green in colour, it spreads at ground level in dense mats and contains a little white flower which five white petals. You can identify it as chickweed if the five are divided by little black lines to give the appearance of ten petals. Chickweed goes to “sleep” at night when it folds it bigger leaves over the emerging tender shoots to protect them from colder tempeatures.

It tends to develop in a great big tangle, it breaks off easily and is therefore tremendously difficult to uproot. Not only will it spread like lightning but it’s also “ephemeral” which means it’s one of those annuals which can go through its reproductive cycle a number of times in the season. “Chickweed can produce 2,500 seeds per plant and move from seed to maturity within two months or so. So you can see why its necessary to keep them down.”

Chickweed yesterday

The best method unfortunately is to just keep pulling out those chickweed nests. Some people put them in the juicer to tap those minerals for themselves. But don‘t try to eat your way out of a chickweed infestation - it was once used to relieve constipation so you‘ll spend more time you know where than weeding. Chickweed is one of those weeds which can be used in compost (before it seeds) to get those minerals back into your soil again.

Scutch grass in the early 19th Century (no cameras then)

Scutch Grass/Couch Grass
Deployed on golf courses and once used to stuff mattresses and upholstery (hence the couch bit), scutch is the long distance runner of the weed world. It establishes itself not only by seed but by laying its stalk out along the ground and setting out little rootballs from each little “elbow” along the shoot. In this way, a single stalk of skutch can establish four plants along a one foot line in less than a week. Unfortunately there’s no easy way of getting it out other than rake out every little bit you find. Watch when you’re strimming, even apparently yellow and dry segments can suddenly reroot and form a scutch plantation. Absolutely do not use a rotivator if you have a scutch problem and Ingrid Foley says, do not let it within a hare’s breath of your compost heap or bin.

There's no Dock holiday at my allotment

Dock
Docks are the bane of my life on Plot 34, where a dock spikes up in almost every fresh bed I dig. These sprout from the hundreds of seeds which the parent plant produces on its “spike” heads. Dock seeds tend to pop up on certain types of ground - usually freshly cleared ground like on a relatively new allotment complex.
The seedlings are not very competitive and are easily snuffed out in grasslands by competing plants. Unfortunately they have a secret weapon - extended suspended animation. They can go to “sleep” and bide their time in the soil for more than 50 years until some eager food growing newbie clears the carpet above and stirs the whole lot from suspended animation.

Once the plant establishes its “tap root” it’s almost impossible to remove and those who have broken the eco code by spraying or injecting them with high powered poisons will note that the dock will waver but will always recover. “I don’t think I’ve ever got the bottom of a dock tap root,” says Ingrid. “This is unfortunate because like a dandelion, they can grow back again. The common types in Ireland are the regular flat leaf (rumex obtusifolius L.) and curly dock (numex crispus). “All you can do is keep cutting off that shoot head again and again to try and deplete the tap root. However someone told me on one of their courses that they dug out a tap root and nailed it to a door where it dried out completely. The thing somehow managed to sprout again.” And they’re everywhere… until that is, you get a nettle sting.

Suspended animation - some weeds can do this even without 1950's scientists

The hairy bittercress
The rather harmless looking hairy bittercress, a common garden weed, has an explosive secret. The bittercress is a booby trap primed by mother nature to be detonated by unsuspecting vegetable growers - just one of many clever and diverse aids to reproduction that weeds deploy in our gardens.
Touching or brushing off ripe bittercress causes the seed pods to literally explode and scatters its payload of 300 seeds per pod to a distance of a metre in all directions.
As an “ephemeral” it’s also fast maturing and can produce seven generations in one growing season. Multiply this by 300 per flower/pod on each plant and you’ll quickly realise why this edible baddie is so hard to eradicate from your plot. The flat rosette shape of the plant even gives it the appearance that it has already “exploded.”

Hairy explosions from the bittercress

It looks like a green rosette or star spread out flat on the ground. It’s stems have individual rounded and succulent-like leaves which reduce in size as they move out towards the tips. The flowers which form at the end of stalks have four white petals. The trick is to get them in spring before detonation. You can eat the younger plants in salads just like watercress.

Shepherd’s Purse
Named after its heart shaped seed pods which are covered in a gummy oil which enables them to stick to clothes and fur. Another ephemeral which can reproduce many times in a season, it has a spray of long narrow jagged harpoon  shaped leaves from a central stem and it sends up long flower stalks with four petalled white flowers on all sides. It was used in WW1’s trenches as a styptic to stem blood flow from wounds and also has astringent qualities to shore up diahorrhea.

Some sticky shepherd's purse yesterday

“With Shepherd’s Purse and Cleavers you can actively bring weeds into your own garden by walking around someone else’s,” says Foley. “This is particularly prone to happen in an allotment complex where people are in and out of their neighbours plots.” Pull it out before it flowers.

Red Dead Nettle
Easy to identify because of its small purple orchid like flowers which poke out randomly from around little upright columns of  spade shaped green leaves. These are thick and wrinkled with a purplish tinge to the top. A single isolated plant can produce 27,634 seeds and it has two other secret weapons. The first is the ability of its seeds to go into suspended animation or dormancy.

Purple hazard - the red dead nettle - not red at all!

This can last five years and in some cases, there have been instances recorded of 30 year old seeds germinating. The second secret weapon is the plant’s symbiotic relationship with the ants. The seeds are coated in a residue which ants feed to their larvae. So ants carry the seeds into their nests and when the seeds have been sucked dry they’re taken to the nest’s “rubbish area” which is rich in nutrients from dead ants and discarded matter.

The Dandelion
Every part of the dandelion is edible although young leaves taste best. Their medicinal use in times past as diuretics to aid liver and kidney complaints has led to the myth among children that contact with them causes you to wet the bed. They come with harpoon shaped leaves, and the distinctive yellow heads are actually a multitude of tiny flowers bunched together. Each turns into a little “parachute” with a feather like canopy which travels on the wind causing a massive spread of seeds which will sprout from a crack in a wall.

(yes I know...)

It’s not enough that 93 species of insect are drawn to them for nectar and pollinate them, the Taraxacum also has the ability to “clone” itself by reproducing asexually just in case. In loose soil, a slow steady pull can sometimes get the entire root up. Otherwise use a “rooter” tool, a sort of metal stick with a sharpened and slightly elevated groove at the end. Chopping the root into parts can cause each part to regrow as a brand new plant.

Creeping Buttercup
With maple shaped green leaves, the creeping buttercup has a huge armoury of assault weaponry including the rapid spread by runner for which is it famous - a sly creeping motion whereby it creates new plants along its spreading arms. It has mass coverage and Rumple Stiltskin level dormancy in its arsenal (80 year old seeds have been recorded to germinate while 12,000 seeds have been recorded in one metre square), animal travel (it’s eaten and excreted by worms, birds and rodents), indestructibility (it survives deep burial and heavy trampling). But most sneaky of all it deploys its own chemical warfare on rival plants- which include your crops.

This dastardly creeper releases substances (allelopaths) which slow their growth. So despite the girly monicker which might suggest butter wouldn’t melt in its mouth, this delicate cup is overflowing with poison. It is a true herbicidal maniac!