Ask a Question forum: Smothering grass in raised bed

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Name: Barbalee
Amarillo, TX (Zone 7a)
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Barbalee
Jun 2, 2016 1:29 PM CST
Hey, I hope somebody can answer this! I'm about to build raised beds on top of my grass lawn. Would it be better to lay down cardboard or 3 sheets of newspaper at the very bottom to smother the grass? The plan is to cover that with some gravel to allow drainage. I'm thinking water couldn't drain through cardboard as well as newspaper, and since the beds will be 12 inches deep anyway, that'll smother the grass pretty well anyway. The "walls" on the bed will be rock. Given all of that, I'm thinking newspaper is best. Am I crazy (as per usual)??
Name: Celia
West Valley City, Utah (Zone 7a)
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Zencat
Jun 2, 2016 1:39 PM CST
It's a good plan as far as it goes. Newspapers and cardboard would eventually break down adding a bit of compost. I'm not sure how long it would take the grass die.
[Last edited by Zencat - Jun 2, 2016 1:39 PM (+)]
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Name: Barbalee
Amarillo, TX (Zone 7a)
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Barbalee
Jun 2, 2016 1:42 PM CST
Thanks, Celia! Would newspaper or cardboard be better?
Name: Tara
NE, Florida (Zone 9a)
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terrafirma
Jun 2, 2016 1:45 PM CST
Sounds like a great plan! Personally, I think I'd use cardboard. It won't break down as fast as newspaper, and therefore do a better job at smothering out the grass.
Name: Barbalee
Amarillo, TX (Zone 7a)
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Barbalee
Jun 2, 2016 1:49 PM CST
Got it, Tara. I figured it would, but I didn't know if water could drain well enough with cardboard at the bottom. Thanks!! Thank You!
Name: Cheryl
Kingwood, Texas (Zone 9a)
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ShadyGreenThumb
Jun 2, 2016 1:57 PM CST
We used three layers of cardboard in my DD's new flower bed. After 1 year, it is flourishing, ground cover and all. Just be sure to cover all of the seams or grass will grow through it. If you want the cardboard to break down faster, at dd a layer of manure before adding your garden soil.
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Name: Barbalee
Amarillo, TX (Zone 7a)
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Barbalee
Jun 2, 2016 2:06 PM CST
Awesome to know, Cheryl! Putting the manure there instead of just mixing it in is a great idea, both for the purpose of breaking down the cardboard and "feeding" the soil above it. Terrific! Thank You!
Name: Greene
Savannah, GA (Sunset 28) (Zone 8b)
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greene
Jun 2, 2016 3:54 PM CST
I would use the cardboard. In our yard we had some tough plants so we put down two layers of heavy cardboard to make a small kitchen garden. You can see the outline of the cardboard under the landscape fabric. I also lined the bed with landscape fabric so the soil would not escape and the water was able to drain just fine. There were zero weeds coming through. Thumbs up
Thumb of 2016-06-02/greene/ca7515

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Name: Sue
Ontario, Canada (Zone 4a)
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sooby
Jun 2, 2016 4:01 PM CST
I would not put a layer of gravel at the bottom. At the very least it will reduce the depth of growing soil plus get mixed in with the bed when you cultivate. At worst it may create a perched water table which impedes drainage and causes the layer of finer soil above to stay wetter. In a raised bed you might actually want the latter since they can dry out, but if that's not your goal it probably isn't a good idea.
Name: Celia
West Valley City, Utah (Zone 7a)
Pour vivre parmi les fleurs
Irises Garden Photography I was one of the first 300 contributors to the plant database! Celebrating Gardening: 2015 Butterflies Birds
Cat Lover Enjoys or suffers cold winters Hummingbirder Plant Identifier
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Zencat
Jun 2, 2016 4:04 PM CST
I was just coming back to say what was already very well said. Thumbs up
Name: Barbalee
Amarillo, TX (Zone 7a)
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Barbalee
Jun 2, 2016 4:22 PM CST
Ah, bless you Greene, Sue, and Celia! Two layers of cardboard it is without question. I had to look up "perched water table" to figure out what that was, and you're absolutely right. The gravel would NOT be a good thing. I was thinking having somewhere for draining water to sit (since I thought it couldn't get through cardboard) would be a good thing, but it's sure not! Man, all of you are both so knowledgeable and helpful...I'm VERY impressed (again)!! Thank You! Thank You! Thank You!
Name: Dave
Southern wisconsin (Zone 5b)
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Nhra_20
Jun 2, 2016 7:24 PM CST
Sand would give you the best draining in soil. Another alternative could be to have an open hole on each side of the bed or the back so it can't be seen. Then inside your raised bed, run some perforated pipe also called drain tile, through the bed from one end to the next and out of the bed. Maybe throw some heavy duty screen over the holes so critters can't get in. But that is what they do around buildings to keep water away from lower levels
Name: Barbalee
Amarillo, TX (Zone 7a)
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Barbalee
Jun 2, 2016 7:34 PM CST
That's a great idea, Dave! I'll go to Lowes tomorrow to see what I can find.... Thank You!
Name: Greene
Savannah, GA (Sunset 28) (Zone 8b)
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greene
Jun 3, 2016 1:39 PM CST
I recently purchased some perforated pipe at Lowe's for a drainage project:
http://www.lowes.com/pd_259817-62059-51910_0__?productId=123...

They also sell a fabric covering to keep the soil/sand from entering the pipe.
Sunset Zone 28, AHS Heat Zone 9, USDA zone 8b~~"Leaf of Faith"
Name: Barbalee
Amarillo, TX (Zone 7a)
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Barbalee
Jun 3, 2016 3:04 PM CST
Superior, Greene! My car is in the shop so I can't get there until Monday ( Crossing Fingers! ). Thanks to you, I know exactly what I need!!! Thank You!
Name: Rick Corey
Everett WA 98204 (Zone 8a)
Sunset Zone 5. Koppen Csb. Eco 2f
I helped beta test the first seed swap Plant and/or Seed Trader Seed Starter Region: Pacific Northwest Photo Contest Winner: 2014 Vegetable Grower
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RickCorey
Jun 3, 2016 3:17 PM CST
>> The "walls" on the bed will be rock.

If the walls are not mortared together or lined with heavy plastic film, water will drain quickly out of the RAISED part of your bed, just through cracks in the wall, or cracks where the wall meets the soil surface outside the bed.

With a raised bed, the only drainage problem will be the part of the bed BELOW grade (lower than the surrounding soil surface. If the natural soil at and below grade is heavy clay, you might have drainage trouble if you want the root zone to extend below grade.

Say you have walls only 8-12 inches tall, like most of mine, and below that is heavy clay. I started out digging down below grade and amending that subsoil heavily inside my bed so the root zone COULD go lower.

But of course any rain flows from the surface down to points below grade. And stays there for days, until it can very slowly "perk" down through the heavy clay.

That's "making a mudbath" or "filling the bathub with mud". (See photo below.) Any root that goes below grade in such a mudbath simply drowns, dies, and rots. It makes plants very unhappy to drive roots down and down until the next rain, when they die back to the level of the water, and then rot. Then they do the same thing again and again, making more roots that just die in each rainstorm. Until the plant dies, too.

IF your walls are lined with heavy plastic,
or you want your "raised" bed to also have a below-grade root zone,
and you have very heavy clay soil,
...
then you might need to create better drainage.

Digging trench big enough to bury perforated, corrugated drainage pipe is a heavy-duty way to do that. The only such pipe I know is 6" in diameter (maybe there was a 4" version?) That requires a wide, deep ditch that you will have to back-fill with pipe and gravel.

If you just want to get a somewhat deeper root zone (say 6-12 inches below grade), and you have a natural slope to work with, it can be easier.

Use a pick or mattock to break up the soil UNDER the bed to the depth you want to make into a DRAINING root zone. Shovel it aside so you can see the hard clay "floor" of your future root zone.

Hack and rake that "floor" to slope uniformly to the lowest point in the local slope of your land.

Now dig a slit trench form the lowest edge or corner of the "floor" towards the lowest nearby point in your yard, where you want rainwater to drain TO.

(Back-fill the sunken and raised parts of the bed with well-draining, airy, amended soil and compost before or after you finish the trench - just make sure you finish the trench before the next rainfall.)

The floor of the trench must start at or below the lowest point of your "root zone" floor.

It has to slope always downhill until you reach the place where you want to lead the water TO.

You can make that easy by just digging the trench by eye AT FIRST. Maybe scrape the floor of the trench with the blade of a mattock. Don't worry if you have some deep holes and small rises at first.

Wait for a heavy rain.

Look at the spot that all the water backed up behind. Take your mattock or shovel and dig away the blockage. The water will rush downhill, filling any holes and eroding away any non-uniform rises. After the rain water has done your "surveying" for you, touch up the trench a little, removing smaller rises, until you have a pretty uniform slope.

During the next rain, water will sink rapidly to the floor of your bed (maybe 12" below grade, surrounded by impermeable clay except for your trench). However, instead of filling the "bathtub" and killing your roots, it will trickle slowly into the trench and out of the bed. As long as thee trench slopes uniformly downhill, water will flow away rather than stay and rise deeper.

That keeps the sunken part of the bed drained, so roots can get the air they need.

I now use narrow slit trenches because I don't have to back-fill them. My yard is already an ankle-breaker, so i don't worry about that. My clay is hard enough that even years later, those trenches still have hard walls and floors. The clay doesn't sag, but they do fill up with grass and weeds.

It is easiest to dig clay when it is SLIGHTLY damp.
- - Dry clay is hard like a rock.
- - Wet clay is sticky and HEAVY.
Spray a little water the night before, and dig while softer, but not sticky.

Until someone explained that to me, I had to CHIP away at the hard, dry clay, with a full-weight pick. Imagine digging soft concrete by hand.

Here's what happens when you arrange for water to flow down out of a bed, but fail to provide any path for it to continue flowing downhill:

Thumb of 2016-06-03/RickCorey/7cec4e

I remembered that "water flows downhill", but forgot the corollary: "and then it stays right there."

The low spot in my front yard leads to a steep slope and several other yards. The runoff that I redirected was only a small amount compared to what already ran off, so i didn't flood anyone out.
Name: Barbalee
Amarillo, TX (Zone 7a)
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Barbalee
Jun 3, 2016 9:17 PM CST
You're amazing, Rick! You've obviously been there/done that when it comes to clay soil. The "wet bed" I originally dealt with is okay, and the flowers are surviving, but it has to go as I don't think the roots are getting enough air because it's still quite wet most of the time! So now I'm in the process of building raised beds. The walls will be un-mortered, un-lined rocks, so water can drain to the outside. I've researched how deep the perennials I want to grow will root, and the raised beds will be taller than that, so the roots won't need to dig down into the clay. I was originally concerned about putting cardboard at the bottom to smother the grass thinking that it might block what water would need to drain straight downward (as opposed to down from the sides of the bed), but I'm understanding that it will take cardboard to smother the grass (instead of newspaper). Now I think that even if the water won't drain straight downard until the cardboard is destroyed, it'll be forced enough to drain through the walls that the bottom of the bed won't be consistently soaked. I could, however put a perforated pipe in the middle angled to drain to the outside. The raised beds will only be 5 1/2 feet wide at the widest point, though, so I don't know if that is even necessary.

When it comes to water, I know you're "The Man"!! Thank You! Thank You!
Name: Rick Corey
Everett WA 98204 (Zone 8a)
Sunset Zone 5. Koppen Csb. Eco 2f
I helped beta test the first seed swap Plant and/or Seed Trader Seed Starter Region: Pacific Northwest Photo Contest Winner: 2014 Vegetable Grower
Avid Green Pages Reviewer Garden Ideas: Master Level Garden Sages I was one of the first 300 contributors to the plant database! I helped plan and beta test the plant database. Charter ATP Member
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RickCorey
Jun 6, 2016 7:07 PM CST
You're very kind!

And usually, someone OTHER THAN me will know an easier way to do a thing.

About cardboard: consider looking up "lasagna gardening". A lot of people swear by that, and many people I respect have said they did some (or all of their) beds this way, and it worked fine.

Instead of digging DOWN the way I do, they only build "up". They lay down corrugated cardboard (1-2 layers), or MANY layers of newspaper, being careful to allow no gaps. Just lay them on top of grass and weeds.Wet them to make sure they stay in place

Then add walls, and add 12-18 inches of COMPOST and compost-makings on top of the cardboard.

Add some soil or pure compost on the very top.

Plant in that. Like growing right in a compost heap.

They say it works fine, and the cardboard "brings the worms".

So water must drain through the cardboard, or run off through the base of the walls.

I wonder if roots can drill DOWN through cardboard, but weed heads can't push UP through it. Just speculation.

But "Lasagna Gardeners" can describe it better, and justify it better, than I can. Since it takes away the digging and trenching that I love, I doubt if I'll ever use it until I get too weak to wield a mattock.

Really, I enjoy cultivating soil more than I enjoy cultivating plants!
Name: Barbalee
Amarillo, TX (Zone 7a)
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Barbalee
Jun 6, 2016 8:22 PM CST
I'll go hunt on it, Rick! I was about to force my poor son to do a lot of digging...he might really appreciate this!! Thank You! Hurray!
Name: Rick Corey
Everett WA 98204 (Zone 8a)
Sunset Zone 5. Koppen Csb. Eco 2f
I helped beta test the first seed swap Plant and/or Seed Trader Seed Starter Region: Pacific Northwest Photo Contest Winner: 2014 Vegetable Grower
Avid Green Pages Reviewer Garden Ideas: Master Level Garden Sages I was one of the first 300 contributors to the plant database! I helped plan and beta test the plant database. Charter ATP Member
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RickCorey
Jun 7, 2016 10:45 AM CST
Maybe your son can do the research for you ... he would be highly motivated!

(I haven't read these yet.)

Here's an ATP-forum-search that turned up four articles:
http://garden.org/ideas/search.php?q=lasagna&button=

and:
http://organicgardening.about.com/od/startinganorganicgarden...
http://www.motherearthnews.com/organic-gardening/lasagna-gar...

I didn't find a "lasagna article" in the classic NGA part of the website.

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