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My backyard is pretty much a weed garden. I have the following concurrent problems:

  • Poor soil (mostly hard clay)
  • Lots of weeds (mostly bull thistle and some dandelions)
  • Dead grass (around 30-50% of it is brown and dead)
  • A few small bare patches

I'm not sure which of these problems I should address first. For example:

  • If I remove weeds, they'll just come back because of poor grass and bare spots
  • If I try to seed/reseed/overseed the grass, it won't remain because of the soil
  • If I try to fix the soil, weeds will flourish even more

One piece of advice I got so far was to blanket it with weed killers and then try to fix the grass. I don't think that fixes the root problem (poor/clay soil), and to make it worse, I have a small vegetable patch growing that I don't want to contaminate with weed killer.

What approach should I take to fix this?

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One should always address the soil before tackling weed and plant issues.

I'm a firm believer that good soil = healthy plants = few diseases and little need for chemicals.

Every plant has a place in which it likes to grow, due to soil composition and climate. Once we understand and accept this principle, its a matter of deciding how to modify conditions to favor the plants we want while making it uncomfortable on the plants we don't want.

So, firstly, you need to discover what your soil is missing. You can either send a sample to a lab for a soil test or you can use your best judgement based on weeds you see that are thriving and a general knowledge of weather and soil conditions in your area. For instance, if you know you get more than 30-40 inches of rain per year, its very likely your soil is acidic and deficient in calcium. Moss is a great indicator of acid soil because it grows where nothing else will. Moss can grow equally well on the top of a brick, which is about what acidic, compacted soil amounts to. Other weeds can indicate other conditions: Yarrow can indicate potassium deficiency. Clover indicates nitrogen deficiency (since clover can fix its own nitrogen from the air). A simple search on google will generate many lists of indicator weeds and their theoretical meanings.

A soil test can help you determine what needs to be fixed, but a soil test is only as good as the sample you send in.

Yes, if you fix the soil, the weeds may flourish more, however if you've designed the soil composition properly, the grass you sow will out-compete the weeds.

Blanketing with weed killers will not address the underlying cause, which is nutritional, therefore the weeds will come right back once the toxin is gone.

See my answer here for more info about calcium, compaction, and moss.

And here for more info about competition between lawn species, particularly clover.

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    In a nutshell, improve the soil so it grows healthy grass that grows so thick it chokes out the weeds. Weeds are the earth's bandaid to protect poor soil till other things take over. – Fiasco Labs Aug 5 '13 at 0:36
  • Just to clarify, you're indicating to fix the soil and start fixing the grass simultaneously, right? – ashes999 Aug 5 '13 at 9:43
  • "For instance, if you know you get more than 30-40 inches of rain per year, its very likely your soil is acidic and deficient in calcium." Our local soils are quite alkaline, and we average just over 40 inches of rain a year. Is that unusual? – michelle Aug 5 '13 at 19:31
  • @michelle you may want to open up a separate question for that instead of discussing it in the comments. – ashes999 Aug 5 '13 at 21:18
  • Sorry for the tangent in the comments! Thank you for your answer, Randy. I'll check the article out. – michelle Aug 6 '13 at 15:53
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Lots of organic matter added to the soil, particularly where you're not growing grass but other plants is the first thing to do. You haven't said what kind of grass you have or want to grow, so that's something I can't address. If its sod and its in a dreadful state, probably best to remove it and then dig the area over and add organic materials to that too. While you're adding organic material (composted materials from your own heap, any kind of composted materials for addition to the soil from your garden supplier, such as animal manures (but not for root vegetables). While you're adding this to the ground, you can also dig out any of the persistent, deep rooted weeds which are present. The addition of humus rich materials (of organic origin) increases bio diversity in the soil, assists in water retention, improves fertility for plants, discourages some weeds (because they like poor soil), helps to make sandy soil heavier and helps to lighten up heavy soil.

UPDATED ANSWER: I know clay soil is very difficult, have dealt with it myself, seems there's only a couple of days in the year where it can be dug - it's either too wet so it sticks in clumps on your fork or so dry its like concrete and needs a pickaxe. Digging with a fork, by the way, is the only way to go, not a spade (or shovel if that's what you call it where you are). If you can't find a day when its diggable, then the lazy man's way will work, but it'll take longer - you just spread organic humus rich materials over the top and wait for nature to do its work. But however you do it, humus rich materials added frequently is the only answer.

  • I have heavy clay, so digging is virtually impossible. I have a separate (raised) garden bed with about an inch of soil on it, but I'm going to leave that as-is for now. – ashes999 Aug 5 '13 at 18:22

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