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the trouble with hawkweed

 
master steward
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So a bee visits the hawkweed and then visits your tomato - thus making your tomato seeds less than viable.  Is that what we are talking about?

 
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I think that's part of it, but keep in mind simple mechanical distribution of pollen (wind, water, walking) likely moves the majority to the immediate locale, in effect "sterilizing" the adjacent soils. Hence the creeping spread of patches like Mary's. Conjecture on my part, but it fits with the reading I've been doing about my local issues...

Around here hawkweed is a secondary allelopath usually found in conjunction with the far worse allelopath, ragweed (Ambrosia spp., usually A. artemisifolia around here). Seems that this is simply a stage of succession around here, and that the soils moved past it to a more wooded stage pretty easily. But your western soils are different as are your ragweed species, and testing has shown some profound results there. I have a LOT more reading to do before I wrap my head all the way around this; you really have broken off a lot to chew on, Paul, but you know how to eat an elephant, right? One mouthful at a time...

While the invasive nature of allelopathic plants is a serious caution, there may be long term benefit in understanding these relations and actions better; non-toxic herbicides and allelopathic cropping are just two thoughts under discussion. And while complete eradication of something like ragweed seems a GREAT idea at face value, it is a valued seed source for many birds and a larval food source for a number of butterflies. I suspect we will find the same sort of associations with hawkweed. Unfortunately (or fortunately depending on your view of moving species of insects about the planet) it looks like insect control of hawkweed is not a likely solution. In any case plant allelopathy is a fascinating and challenging topic, and I look forward to the discussion...

HG

 
paul wheaton
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I think the issue is the same as many weeds:  spraying is really not the answer.  You have to outcompete it.  If you keep your land fallow, it is only reasonable that something will pop up there.  If your soil is compacted and acidic, it is only reasonable that hawkweed will pop up. 

In fact, I would think that if your acidic, compacted soil were loaded with something else, hawkweed would never get established.  Or ... further ... if it did, then it would be hardly noticeable. 

And then there is another upside to hawkweed.  If it is the only thing growing in a spot that has some really barren patches, it would seem that hawkweed might make an excellent pioneer species (at least when my brain forgets about the pollen based allelopathy).  I wonder what it's root structure looks like.  I wonder if it's a DEEP tap root.



 
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Hi Paul,
Thanks for not beating me up.  I did have you half answered on Friday when I made the error of a non-blogger and went to post it after my log-in had timed out – lost everything!  So this time I’m writing it up as a document, will have to log-in and then copy and paste.

paul wheaton wrote:

Cool!  I'm a known entity in your world.  I feel all celebrity-ish or notorious or something!



I actually had an acquaintance many years ago, his name was David who was involved with permaculture, I think he was also involved with starting the “Tilth” magazine.  So my understanding of the principles go back many years, anyone who is able to implement the principles on the ground is a celebrity in my eyes.

paul wheaton wrote:

True.  Although lately I've been trying on "symbiotic".  I think I like "symbiotic".



Symbiotic is a good word.  Trying to live in symbiosis with another organism(s) is a laudable goal.  However, being in symbiosis with another organism (such as a spouse) is difficult enough when you speak the same language, when you don’t, you can only guess you are "there" when things are running smoothly between you.

paul wheaton wrote:

I'm familiar with knapweed (and I'm tempted to start a new thread to talk about that).  The alleopathy is niacin via the roots, right?  (In the new thread I'll has how the bio control is going)



This is what I found out about knapweed from this site:  http://4e.plantphys.net/article.php?ch=&id=377:  Using this approach, the phytotoxin present in spotted knapweed root exudates was identified as a racemic mixture of (±)-catechin (hereafter catechin) (Figure 2). Bioassays with the two enantiomers revealed that they have different effects. (−)-Catechin is a potent phytotoxin, whereas (+)-catechin is a weaker phytotoxin with some antimicrobial activity (Bais et al. 2002, 2003; Veluri et al. 2004). Purified catechin from spotted knapweed root exudates and commercially available catechin acted similarly against a wide variety of plant species in bioassays, suggesting the chemical identification was correct. While catechin was identified as the principle phytotoxin in spotted knapweed root exudates, other chemicals in spotted knapweed root exudates or plant tissue may have similar phytotoxic properties. Further, spotted knapweed may produce other phytotoxic compounds when grown under more realistic field conditions, as opposed to the highly artificial laboratory conditions used in these experiments. In the model plant Arabidopsis thaliana, distinct root exudation profiles are associated with different stages of development (Walker et al. 2003); thus it is possible that spotted knapweed may secrete different phytotoxic compounds at different stages of development.

However, at this site:  http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2676754/: Our paper strongly supports the view of others that (-)-catechin is not an allelochemical. This very weakly phytotoxic compound is found in exceedingly low concentrations, if at all, in the soil in which producing plants are found. Furthermore, it is very unstable in soil and in water, and its derivatives do not appear to be significantly phytotoxic. We hope that the findings that challenge the view that (-)-catechin is an allelochemical do not discourage others from initiating or continuing research in this intriguing area of chemical ecology.

Knapweed bio-controls… Yes a new topic would be in order.

paul wheaton wrote:

What does the hawkweed do?  I've seen patches where there is heaps of it.  Yet it still seems like other plants are outcompeting it.   It's leaves are so low to the ground, it seems like it just isn't gonna do well.    Yet there are lots of blooms. 



I was less successful at discovering what hawkweed does.  There are studies on some species that indicates allelopathic properties (such as mouse-ear out of New Zealand), but the only other study I found would have required purchasing the $10 article that I just don’t have the funds to do.

There have been studies on what both plants do in the rhizosphere.  How the mycorrhizae associated with the weeds interacts with the mycorrhizae associated with neighboring grasses.  Primarily, the weeds steal carbon from the grasses at this level.  The weeds are pre-adapted to our low nitrogen soils, so throwing nitrogen on them makes no difference to them, but it does to the grasses, helping them to compete.  Again, this can be accomplished at the home owner level, but not at the landscape level. 

paul wheaton wrote:

And then I see areas where the soil is pathetic.   It seems like nothing would grow there, but a few hawkweed plants are making a go of it.  And in these cases, my thinking is I should throw some seed down that will improve the soil.  But in the meantime, at least something is turning the dust into some kind of life. 



On pathetic soils, we have our own “weeds” (such as fireweed) that should be doing the job that the hawkweed is doing, but they can’t compete.  Remove the hawkweed and they will come up.

paul wheaton wrote:

But I have yet to see a powerful infestation in a pasture or in the wild.  Are there such occurrences?  If so, how common is that?



If you are in Missoula, my guess is to travel north toward Columbia Falls and follow the powerlines up toward Hungry Horse Dam.  When I conducted a survey there, about 15 years ago, orange hawkweed was invading neighboring lawns, my guess is that it has spread throughout the powerline and into the surrounding forests by now. 

If you travel west into Bonner County Idaho in early June, you will see a multitude of orange and yellow blooms through fields and forest meadows.  Continue west then north across Pend Oreille County and west into Stevens County and you will see more of the same.  Ferry County has mounted a valiant effort over the years to stop encroachment, but with pressure from the west, north and east, it may be a losing battle.

paul wheaton wrote:

If the deer are eating it and getting sick, then I guess it is toxic - but is this a case where they are out of other browse, but the hawkweed has managed to still be edible?



A big “if” as it is only speculation on my part.  Apparently hawkweed is edible, (you can see where it’s been grazed) but our deer do not recognize it as toxic.

paul wheaton wrote:

Two things:

1)  how sure are you that the seeds become viable after the flower is cut?  I would think that seeds might still form (unlikely) but they would not be viable.



This has been studied, although I have nothing to cite on hand.

paul wheaton wrote:

2)  I think that if mary mows at 3", then the clipping of the flower stalk does only a little damage to the plant, but the real power is that the turf gets much thicker and healthier and is then better able to outcompete the hawkweed.  And if there are seeds being spread, it will matter little since the seedlings won't stand a chance against the turf of awesomeness.



If you have had success mowing at 3”, and that’s what it takes to get a “turf of awesomeness”, then that’s the best bet as you are correct in the healthier the lawn, the less even hawkweed can compete.

The Wicked Weed Cop of NE WA.
 
paul wheaton
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The new knapweed thread is here:  https://permies.com/permaculture-forums/2962_0/organic-practices/understanding-knapweed

If you are in Missoula, my guess is to travel north toward Columbia Falls and follow the powerlines up toward Hungry Horse Dam.  When I conducted a survey there, about 15 years ago, orange hawkweed was invading neighboring lawns, my guess is that it has spread throughout the powerline and into the surrounding forests by now.



I get to visit lots and lots of places and torture kind people with my obnoxious opinions. 

So I've seen yellow hawkeed in damn near every neglected lawn in seattle.  They like to call it "dandelion" and when I try to explain the difference their eyes glaze over. 

I have seen it, and beaten it (smothering with moldy hay), on a farm I used to have on mount spokane. 

I have seen it in a valley pasture in eastern oregon where my kin, who I thought were keen on organics, loaded up a sprayer and spent the better part of a day spraying it. 

Ferry County has mounted a valiant effort over the years to stop encroachment, but with pressure from the west, north and east, it may be a losing battle.



What does a losing battle look like?

Everything I have seen just didn't bother me that much.  Anything I have done was to assuage the people freaking out about it - nothing like "everything is covered in 20 feet of kudzu!"  or "it is one big ocean of blackberry brambles!"  Or knapweed.  Or leafy spurge.

The neglected lawns in seattle had a lot - but for my friend, I just adjusted his mower height and now it is almost all gone from his yard.  Easy peasy.

Apparently hawkweed is edible, (you can see where it’s been grazed) but our deer do not recognize it as toxic.



Maybe it's one of those things like snowberry.  Just toxic enough that they will eat just a little each day.  But when you're hungry, a little snowberry brush (buckbrush) will get you by.

This has been studied, although I have nothing to cite on hand.



I'm cool with you shooting from the hip.  I don't need a bibliography.  I'm just feeling around for a bit more qualification.  I would think that if it is a flower and not yet a puff ball, then .... I suppose it is possible.  It just seems so unlikely that the process will finish. 

The Wicked Weed Cop of NE WA.



You should put that in your profile signature.  It's awesome. 

It's good to hear from a weed cop that gives a damn about the science.  I remember attending a weed cop thing in spokane once.  Basically it went like this:

"Here's a slide of knapweed.  This is a noxious weed.  Treatment is to spray it.  Here's a slide of canadian thistle.  This is a noxious weed.  Treatment is to spray it.  Here's a slide of bindweed.  This is a noxious weed.  Treatment is to spray it.  ..."  spray it, spray it, spray it, and the presentation is over.  Sometimes they would have little talks about what makes the best spray. 


 
Scott Reil
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I KNEW I was looking forward to the discussion...

Paul, kudos for a site where cognoscenti show up to post. Shows you are doing things right..

Sharon, thanks for the time and effort. I just got smarter (I know, it's relative, but thanks anyway...)

Again, Paul's basic recommendation for higher cutting remains the best advice to beat hawkweed (and clover, and dandelions and black medic, and thistle and all the other's...)

"Here's a slide of knapweed.  This is a noxious weed.  Treatment is to spray it.  Here's a slide of canadian thistle.  This is a noxious weed.  Treatment is to spray it.  Here's a slide of bindweed.  This is a noxious weed.  Treatment is to spray it.  ..."  spray it, spray it, spray it, and the presentation is over.  Sometimes they would have little talks about what makes the best spray. 



Don't it just kill ya? Literally...

HG
 
paul wheaton
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helpfulgardener wrote:
Paul, kudos for a site where cognoscenti show up to post. Shows you are doing things right..



Cool - I don't have the answer, but I get some of the credit.  I like you. 

So here is what we have so far:

Hawkweed is definitely allelopathic.  Probably in more than one way.  One probable way is that hawkweed pollen will attempt to prevent the seeds from other plants from germinating. 

Does that sound accurate?
 
paul wheaton
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Still hoping that somebody that knows more will help us fill in the blanks.
 
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I just did a quick web search. Apparently timothy and corn pull the same dirty trick on their competitors. I would expect self-pollenating species like peas and wheat would be relatively immune to this effect, but I wonder how the third sister (pumpkin) avoids problems with corn pollen. That makes me wonder if there's another layer of cooperation to this famous guild: while pumpkin competes for animal pollenators, corn blocks wind-pollenated species from reproducing.

A more in-depth article (Stephen D. Murphy and Lonnie W. Aarssen, American Journal of Botany 82(1) pp.37-45, 1995) showed that, in the case of hawkweed vs. fabacae species, some water-soluble, acidic substance prevents the pollen from germinating (i.e., the pollen sits there, rather than reaching out for the ovum). Remarkably, a given insect tends not to visit both types of plant in the same outing, and when the scientists went out and looked, they didn't find much hawkweed pollen on, say, alfalfa or vetch stigma. Maybe pollenators have adapted to this method?
 
paul wheaton
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I went fishing for more information along these lines today and received this from Lacy Malloy:


By hawkweed do you mean this: http://en.wikipedia.org/wiki/Hawkweed ; ?

If so it is a pollen allelopathy - inhibiting seed germination from what I've read online.  http://www.jstor.org/pss/3988569

"Pollen allelopathy results when pollen releases toxins that inhibit seed germination, seedling emergence, sporophytic growth, or sexual reproduction. Of the six known pollen-allelopathic species, two are crops (timothy and corn and four are weeds (orange hawkweed, parthenium, yellow hawkweed, and yellow-devil hawkweed). Allelopathic pollen in weeds could pose threats to crops, especially if both are wind pollinated. Even if it is the crop that is pollen-allelopathic, other crops could be threatened, or more likely, weeds might adapt to pollen allelopathy and pose a greater problem. Nonetheless, pollen allelopathy could be a useful approach to biological control because allelochemicals are packaged in a natural targeting system (pollen grains) and are biologically active at low doses (< 10 grains/mm2 on stigmas). If it is to be an effective biological control agent, pollen allelopathy must be examined within the wider context of farming systems management and used as one method of varying selection pressures to prevent weeds from adapting to any one particular management technique or suite of techniques."

Sunflowers and other asteracea family plants are used in phytoremediation,  perhaps you might find additional information under that topic? I haven't looked myself.

good luck!

Lacy



Wow!  Some really excellent info!


 
paul wheaton
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And more.  This time from Michel R. Wiman



Hi Paul,

I used to work as a research assistant to Dr. Linda Wilson at the PSES Dept. at the  University of Idaho. She will know all the details of hawkweed allelopathy, so I defer to her. As I recall, the native herbivore that in Europe reduces daughter rosettes coming from the runners of the plant don't exist in the US; causing invasion, not a chemical response. There may have been an introduction of one of the natural enemies to control it - either a wasp or a midge - in recent biocontrol programs.  But, I am not an expert. It does, however, have barbed hairs on the stem causing irritation of nasal tissues....may not be a great dried flower as your posts wondered!

Best regards,
Michel
*******************************************
Michel R. Wiman
Research Associate, Small Farms Program
Ctr for Sustaining Ag & Natural Resources
Washington State University TFREC



I wonder which herbivore was the muncher?  I wonder if there could be a way to persuade a local herbivore to find these more tasty?

 
paul wheaton
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And more:



Paul,



I am in Deary, Idaho and have had hawkweed (mostly yellow, but some orange) spreading for the last 9 years.  My ground is certified Organic, so spraying is not an option.  We have tried mowing, but that has to be done at very specific times to catch the flowers before they mature and it has to be done several times.



Since hawkweed propagates 3 ways (seed, runners and rhizomes), it is very invasive.  It poisons the ground for the grass around it.  According to the Charles Walters book Weeds - Control Without Poisons, increasing the soil pH rots the rhizomes.  Increasing soil pH is complex, so we are still working on that.  We have been experimenting with soil pH increase as well as planting clover (red and white) and have had sheep graze it heavily just this year.  The Sheep love the flowers, so that eliminates the pollen and seeds.  We don’t know how well the clover will work on hawkweed, but we have found that red clover will run out oxeye daisy, another of our noxious weeds.



I don’t know if this is helpful, but hawkweed very definitely fits the definition of weed (changes its environment to suit itself, grows thickly and chokes out more desirable plants.



Daryl Swanstrom,

Tourmaline Farms

 
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I just discovered your website today as I was researching ways to conquer yellow hawkweed. We have a place in a remote area of the West Kootenays in British Columbia and both Yellow & Orange hawkweed has been spreading along the roadsides for the past few years; including along the ATV, logging & forest service roads that lead to the high alpine & mountain caribou habitat.
My personal 'fight' with the hawkweed is along the roadside adjacent to our property. I've managed to remove 90% of the tansy, 80% of the white, yellow & pink clover, 80% of the dandelions, 50% of the oxeye daisys, and 50% of the non-native buttercups. Every few years BC hydro hires a contractor to 'slash-cut' the roadsides of whatever shrubs & small trees are threatening to grow up under the power lines. 2 years ago their slash job was drastic, cutting all the native willows & thimbleberry bushes to about 6" from the ground. This has had both negative & positive impacts. Where there had been an almost inpenetrable mass of willows & thimbleberry; there are now dogwoods, dwarf woodland roses, bunchberry, strawberry, ferns, bog orchids, pink daisies, fireweed, asters, pink wintergreen, violets, goatsbeard (Aruncus sp), and this summer I even found a Calypso orchid. Of course the willows & thimbleberry are growing back, I am now keeping them under control to allow for greater diversity; and hopefully to prevent another slash next time around - in other words I am hoping it will be obvious that a slash is not necessary.
On the negative side the roadside weeds are now trying to encroach down the rather steep bank where I'm valiantly trying to promote the native wildflowers. As our time there until recently had been limited to spring & fall holidays, I did my best with manual removal of the weeds. However last fall I ran out of time at the far end of our roadside & there was about 4' of roadside that had a few scattered yellow hawkweeds left as well as few dandelions, daisies, buttercups, etc. (no tansy though). This spring those few scattered hawkweeds had become a solid mat of hawkweed, covering about 20 square feet. Valiantly I pulled up all of this mat - roots, runners, rhizomes & all - not realizing how much seed was in the ground! (By the way the root system is shallow & fibrous - it sometimes comes up as you pull on the flower stem). After weeding the rest of the roadside & roadside bank we then set up a sprinkler system on a timer hoping that this would favour the natives. I now have another almost solid mass of yellow hawkweed covering an even larger area - close to 100 sq. feet. The rest of the roadsie & bank is doing wonderfully & the natives are winning - but for how long?? The Hawkweed army approaches!!! I can't mow - this is not a lawn - I have no lawn actually. Other than the building site we have woodland & a large moss bed where I have been planting native wildflowers (and no, I don't dig up native wildflowers).
I realize part of my problem is poor soil - it is a roadside. Any suggestions?? If & when I manage to conquer our roadside my goal is to tackle the surrounding roadside areas - hopefully with the support (if not the help) of my neighbours - some of whom like to have a little hawkweed & tansy growing in their garden!! Yes I'm trying very hard to educate them on invasive plant species but it is an uphill battle.
 
                                  
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If you had a dense hawkweed area, could you put some chickens on it, do what you normally wouldn't and leave them fenced there till the hawkweed is gone?

I bet a salcata tortoise would eat them, we have one as a pet that eats pretty similar weeds, and one lives for 100 years, they might eat a lot.
 
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I think it's bearded hawkweed that's working on taking over Kodiak Island, but boy is it working fast, turning once lush wild pastures, grazed by dear and bears, into monoculture.
 
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The ecosystem here, as with the Puget Trough, is balanced from the substrate rock and the plants and animals that have co-evolved here.  Our soils are naturally acidic, low in nitrogen, and ours here are high in phosphate (I don't know about the west side).

The problem with noxious weeds (which only means they are illegal (in WA) due to being invasive, difficult to control and damaging -- economically, to the environment or a threat to human health) is that they are pre-adapted to our ecosystem and have developed the ability to better harness the available resources. 

The reason we pick on gardeners is that the weeds easily escape the garden environment into the larger ecosystem where they upset the delicate balance between our co-evolved native plants and animals.  Noxious weeds have been documented as second only to land development for loss of our native biodiversity.  From an ecosystem perspective, this is disastrous. 

When hawkweed infestations reach a landscape level (which several species have in my corner of the world), the effects start to cascade.  At this time the outcome is unknown, but I have developed some suspicions.

Are you co-evolved with the plants and animals "native" to this area? What does this say about your existence here? Have you ever thought of going after land development ("the most damaging to...biodiversity"), rather than scapegoating weeds which colonize anthropogenically-disturbed areas? There's a well-documented fossil record of organisms colonizing vast areas as niches open up and climate changes (read Invasion Biology: Critique of a Pseudo-science). In my opinion, you sound kind of paranoid, and have control issues splashed with a short-sighted perspective of ecology.
 
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I'm in the Superior National Forest, the orange hawkweed is pretty, grows with white n yellow flowers and colors up the roadsides. If my soil is acidic n compacted ill let the plant do the work. It's considered invasive but my land hasn't been messed with by man. Oooh baby I like it raw.

Using my phone, don't see a way to load pics... Might have to attempt this next time I do laundry.
 
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Paul and I talked about dealing with all the hawkweed in our pastures in a podcast (not yet released).  We have a 40 acre property south of Portland in Beavercreek.  It has 15+ acres of pasture, and there's a lot of hawkweed.  Also Queen Anne's lace, or wild carrot.  Also Doug firs, although those aren't in the pastures!

I'm hearing that it grows in acidic infertile soils: check, check.  Paul pointed out that in the area where we had the cattle while we were feeding hay last winter, there is no hawkweed.  I don't think cow poop is basic, but it certainly increases the fertility of the soil, particularly combined with the hay they wasted.

We scattered crimson clover and rye seed on this area of compacted and almost completely bare soil this spring, and it's mostly growing those two species.  The rest of the pastures are going golden with the seasonal lack of rain, but that area is impressively green in comparison.  So, one strategy is to locate the small cattle herd (<10 Dexter cattle, so a small herd of small cows) on the worst patch of hawkweed this winter.  

Curious to see if anybody has come up with new strategies in the past few years.
 
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I have also become very interested in hawkweeds and their allelopathic properties!  Mary, your hawkweeds are "mouse-ear hawkweeds" and they have an additional reason they form such a heavy mat of weeds.  They have runners like strawberries which allows them to grow very close to each other in spite of the fact that neither their own seed or other plant seed can germinate close to the parent plant.  Orange hawkweed and mouse-ear hawkweed are the two I have seen mentioned most often as allelopathic.  Also I have seen lots of statements such as most "hawkweeds are allelopathic......"

The hawkweed I am most interested in is autumn hawkbit also called fall dandelion.  I have never seen this plant in my city, only in cities 30 or so miles away,  but I planted a dozen plants in my boulevard lawn 2 falls ago and they all survived the winter.  So this fall I brought back another 30 plants and planted them.  I also brought back from another city a large coffee cup full of the "dandelion fluff-like" seeds and spread them around in the grass....

So I have a large boulevard lawn with impossible growing conditions.  There is poor thin soil on top of 20 feet of sand all in the blazing sun with heavy foot traffic from a public school across the street.  My plan for the last two years has been to attempt to grow a lawn green all summer with:
1) no watering
2) no fertilizer
3) no pesticides or weed killers
4) less mowing
and 5)  while I'm at it, why not flowering and pretty and bee friendly as much of the summer as possible.....

So while I love dandelions with their cheery yellow flowers, and they satisfy MOST of my requirements - they stay green thru any drought,  they require no work at all, or watering or fertilizer or anything - THEY DO NOT PLAY NICE WITH OTHERS!  Eventually, you have nothing BUT dandelions....  And that is where "fall dandelions" come into my interest.  They are like smaller delicate dandelions with smaller delicate flowers and especially narrow more delicate leaves that let grass and other plants live right along with them.  And amazingly they spread out in a nice orderly fashion all across the lawn with about 5 inches between each plant.  And even more amazing, the allelopathic nature which keeps them from growing a mat of their own,  also seems to inhibit regular dandelions from sprouting!!!  So maybe I can soon stop hand weeding the dandelions - apparently the seed bank  of dandelion seeds in the soil only lasts for a year or two...

Other weeds that I'm "all in" on so far are bird's foot trefoil with beautiful yellow flowers in the worst heat and drought,  red, white, and yellow clovers which are quite drought resistant and pretty, crown vetch with pink flowers, cow vetch with purple flowers, heal-all with purple flowers and also unlike most weeds keeps its leaves thru the winter along with the grass,  Indian strawberries with yellow flowers and red berries thru-out the summer,  Siberian squill for very early blue flowers,  violets for late spring flowers....and the jury is still out on some knapweeds, some mustards, some bindweeds, queen anne's lace,  camomile, yarrow, etc.

I'm interested in any suggestions of other weeds or unusual grasses which readers have found to fit my criteria....

ray979
 
You'll never get away with this you overconfident blob! The most you will ever get is this tiny ad:
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