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My backyard is completely (seriously, completely) infested with weeds -- bull thistles (or spear thistles) and dandelions (the common yellow-flower weed), to be specific.

enter image description here Bull Thistle (source: Wikimedia commons)

[][2] Dandelion

How do I get rid of these things without the back-breaking effort of uprooting them all (there are probably too many), or the expense of paying a professional service for it?

I've heard vinegar works well (albeit it kills grass too), but I'd like to hear if there's another natural, inexpensive way to get rid of these nasty weeds.

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Yes I think you'll need physical removal. Thistles are nasty things when it comes to bare feet of all ages! I've found spot weedkillers do work on them but they need more (and stronger types) than dandelions. Stronger treatments are more of a problem with kids of course. So physical removal it will probably have to be... –  winwaed Sep 7 '11 at 1:40
    
@ashes999 I've edited your question to mean thistles instead of dandelions as per your comment and cleaned up the comment discussion here related to dandelions. –  Lorem Ipsum Sep 7 '11 at 2:09
    
@yoda I appreciate it, albeit that dandelions are probably 80% of the infestation, not bull thistle. –  ashes999 Sep 7 '11 at 10:30

5 Answers 5

up vote 5 down vote accepted

Now that the question has been updated to include "Thistles" I've revised my below answer a little...

Credit for the "dandelion" part of this answer goes to my mum.

Dandelions:

When we (wife and I) moved into our current home 4 years ago, the front and back lawns were covered in dandelions (and other broadleaf weeds). I didn't want to go the herbicide route, and after speaking with my mum, she said the only way to truly get rid of (control) dandelions is to hand remove them (important: you need to remove root n' all) and recommended using a small hand garden trowel for doing so.

I didn't have a "small hand garden trowel", instead I bought a small (and cheapish) builders trowel and used that for 3 years:

Dandelion remover - small builders trowel

Then last year on clearance (paid $1) I picked up a Fiskars Softouch Weeder:

Dandelion remover - Fiskars Softouch Weeder

Both of the above hand-tools have worked well in removing dandelions (roots included).

  • The first three lawn cutting seasons I pulled a lot! of dandelions, at least once a week I would walk the lawns and hand remove all the unwanted plants I saw (all of them went into a plastic bag for offsite disposal).

  • During last year's lawn cutting season I noticed a big drop-off in the number of unwanted plants I was removing, except for crabgrass (but that's a whole other story).

  • This years lawn cutting season I've only had to remove a handful of "small" (young) dandelions, this is to be expected as I can't control dandelion seed heads blowing into my garden (though I wish I could).

  • Yes, getting any unwanted plant under control via an "organic" approach is going to take patience and time, but if you stick with it, you will see (excellent) results.

    • And bare in mind, even if you go a "non-organic" route, you're pretty much "forced" to continually use the chosen method if you don't want to see the unwanted plant(s) return.

If you wish to read more about how I approach "organic" lawn care, go here on SE:

Thistles:

Personally I haven't had to deal with thistles in my lawn, that said I do occasionally have to deal with that unwanted plant (weed), along with dandelions and spurge in our street's common ground (flowering) areas that I maintain (I don't mow the grass, a lawn care company takes care of the mowing):

I remove "smaller" thistles using the above tools, basically I treat its removal the same as dandelions ie Remove the unwanted plant, root n' all.

For "large" thistles I use a spade to dig them out (root n' all). After digging them out I back fill the holes with some suitable material and make good the area.

Good luck!

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Whilst I share your preference for the non-chemical route, I think your best course, given that this is a serious infestation, is to spray the leaves with a systemic weedkiller, such as Roundup, which will spread into the roots and kill them. Make sure that the dandelions are growing actively - mid to late-spring is probably the best time - and that there is enough leaf area to spray the weeds fully. You will probably need to spray them at least twice.

Short of hand-weeding, an alternative natural strategy (although less effective than the chemical one) would be to spread corn gluten meal over the whole area, cover it with black plastic sheets and weight them down. This will deprive the weeds of water, and of light which will prevent photosynthesis, and will eventually kill most of them - but it will take some time.

Update:

I hadn't realized that the weeds were in your lawn, and I can understand why you wish to avoid using chemicals, given that you have young children. In the circumstances, hand-weeding would seem to be the only way forward; this tool has received excellent reviews and would take most of the backache out of the operation.

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A decent solution (corn-meal), except it will kill a lot of my grass, too. I have young children, so chemical is not something I want to consider; if it comes to that, I'd rather hire someone to uproot them all. –  ashes999 Sep 4 '11 at 15:42
    
I hadn't realized that the dandelions were in your lawn; and I can understand why you wish to avoid using chemicals, given that you have young children. In the circumstances, hand-weeding would seem to be the only way forward; this tool amazon.com/Fiskars-7870-Uproot-Garden-Weeder/dp/B0030MIHAU/… has received excellent reviews and would take most of the backache out of the operation.. –  Mancuniensis Sep 4 '11 at 16:18

The weed&feed weedkillers are going to be insufficient for thistles, but should work on the dandelions. I think the thistle should be the priority though - it is spiky and looks bad.

Your options are physical removal or weedkiller: no free lunch, here! I would use a systemic "kill everything" weedkiller. You can use it as a spot treatment and if you get the thistles when they are still small, it is easy to apply to the crown without catching anything else nearby.

Yes this can pose a problem with kids, but you only need to ban them from the lawn for a week or so (read the instructions on the weedkiller). This should not be a problem if they are already refusing to walk on the lawn due to the spines. You could also try fencing off sections as you treat it?

Remove the dead thistles with a spade as the spines will still hurt. They should compost okay, but remove all seed heads and trash them (do this before the weedkiller as the seeds will only spread).

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Nobody touched on a few points to help control dandelion and thistle so I thought I'd add my 2cents even though this is an old thread. Also I'm curious how you made out since this is an old thread.

Dandelions grow well in alkaline soil which most grasses do not. If your soil is alkaline your grass could be thinning leaving room for dandelion to grow. Do a soil test with your local university cooperative extension and make any changes to pH and fertility. It will do a lot to help thicken your grass to help prevent weeds.

Set your lawn mower to the highest setting to help shade out new seedlings. It's also good for the grass. Water and fertilize appropriately. There are other things that might be keeping your lawn from growing thick such as dull mower blade or disease. Try to figure out what the problem is and correct it. A healthy, thick lawn is a big factor in controlling weeds.

One popular weeding tool that works well for dandelions and other weeds that have a long tap root is the Weed Hound Elite (check the link for my thoughts on it on my site). It's nice because you don't have to get on the ground to weed and it works very well.

You can spot spray the weeds in the fall using an organic herbicide such as vinegar. Spray them, wait a week, if they start coming back spray them again a week later. Do this for 2-3 weeks and you'll drain a lot of the reserves from the roots. A combo of the weed hound and spraying works well. Then reseed those areas of the lawn.

Check out Organic Lawn Care for the Cheap and Lazy. There's more info on proper mowing, fertilizing and watering and specific info on dandelions and thistle.

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My soil is mostly clay. I didn't do well -- manually pulled them with something like what you pointed out. Two years later, still lots of dandelions in spring, but not much beyond that. Maybe the same will work for thistle over the next two years. I have a few veggies growing (and two young kids) so herbicides are out. +1 –  ashes999 Sep 6 '13 at 3:16
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I don't know about dandelions growing well in alkaline soils. pubs.aic.ca/doi/pdf/10.4141/P01-010 says "It grows in soils ranging in pH from 4.8 to more than 7.6". Also, there aren't many alkaline soils east of the mississippi, yet dandelions abound. Mowing high is good advice though. –  Randy Sep 6 '13 at 6:58
    
@ashes999 soil testing is one of the best things you can do when you are having issues in your lawn. If the lawn grows well there's less room for weeds .Here's a list of laboratories in your area. omafra.gov.on.ca/english/crops/resource/soillabs.htm On that site I also found info about a product I never heard of before. It's called Sarritor. It's a fungus (Sclerotina minor) that kills broad leaf weeds including dandelion but doesn't affect grass. omafra.gov.on.ca/english/crops/hort/news/vegnews/2010/… Unfortunately it does infect some vegetable crops. –  OrganicLawnDIY Sep 6 '13 at 11:15

I know it seems like I'm carrying the "calcium" flag on this site as it seems calcium is the answer to almost any problem, but once again, if you want to be rid of dandelions, check your calcium levels:

enter image description here "The lawn on the left received applications of high-calcium limestone and gypsum; the lawn on the right did not."

Read more at: http://www.safelawns.org/blog/2010/11/guest-blog-to-reduce-weeds-and-improve-lawn-apply-calcium/

Another testimonial from a credible source can be found here: Calcium Works! Not A Single Dandelion!!!

I'm a believer that each plant has its perfect soil conditions where it competes well with other plants. Clover competes well with other plants in a low-N soil. When the N levels are raised, clover doesn't compete as well as grass and the clover goes away over time. Likewise, dandelion competes in low-calcium soils. Or maybe it's better to say dandelion competes in high-potassium soils... which is really saying the same thing.

enter image description here

Image taken from http://www.soilandhealth.org/01aglibrary/010141.soil.fertility.animal.health/010106ch02.html

What this image is saying is simply when rainfall has leached calcium to the point that it is no longer the dominant mineral, then potassium becomes the dominant mineral in the soil.

Why am I bothering to tell you this?

BIOLOGICAL WEED CONTROL VIA NUTRIENT COMPETITION: POTASSIUM LIMITATION OF DANDELIONS

Weedy plants are often controlled by the application of herbicides. Here we explore an alternative method of control. We suggest that the abundance of an undesired plant species (here dandelions: Taraxacum officinale) may be controlled by modifying interspecific competition via changes in resource supply rates. This hypothesis is supported by several lines of evidence. First, analyses of effects of different patterns of fertilization on plant-species abundances in the 140-yr-old Park Grass Experiment at Rothamsted, England, show that Taraxacum abundances were highly dependent on potassium fertilization and on liming, but not on addition of other nutrients. Potassium fertilization led to a 17- to 20-fold increase in Taraxacum abundances in the classical Park Grass data, and to a 4- to 7-fold increase in the modern data. Liming led to a 2- to 3-fold increase for classical data and to a 3- to 4-fold increase for modern data.

Second, in a greenhouse study in Minnesota, Taraxacum had a higher requirement for potassium and had its biomass more limited by potassium than any of five common grass species of Park Grass. This suggests that Taraxacum may be a poorer competitor for potassium than these grasses, but this mechanism has not yet been tested. Third, in a series of Minnesota lawns that had not received fertilizer or herbicides, both Taraxacum density and abundance were significantly positively correlated with its tissue potassium levels.

This demonstration that desired and weedy plant species can differ in their resource requirements suggests that adjustments in resource supply rates may determine the outcome of interspecific competition, allowing desired species to competitively control weedy species. In particular, for soils with low potassium levels, the use of potassium-free lawn fertilizer is predicted to decrease Taraxacum because of competition from grasses like Festuca rubra.

The best way to lower potassium levels in the soil is by raising calcium levels.

Conclusion

If you raise calcium, it will dilute potassium in the soil and make it very uncomfortable for the dandelions, but the grass will love it.

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How practical is it to buy and apply calcium to an entire lawn? –  ashes999 Sep 6 '13 at 10:40
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Very practical. Applying lime or gypsum is part of the maintenance plan of 1000s and 1000s of people, including me. Lime is cheap, about 8 cents a lb here. If you had a 10,000 sq ft lawn and applied at the rate of 10lbs/1000sq ft, it would cost $8 and be much easier than digging up weeds. Spending my time digging weeds, to me, isn't very practical over an entire lawn. –  Randy Sep 6 '13 at 16:39
    
Okay, I'll give it a shot. Thanks. –  ashes999 Sep 6 '13 at 18:30

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