Here is your answer, and maybe more info than you were looking for. Somewhere along the line, I'll mention oxalis.
The good news!
My first raised bed--the one *I* made with the salvaged (FreeCycle) concrete blocks and filled with the various composts and vermiculite and (heaven help us) peat--was approx. 8" deep. I just didn't believe Mel's statement that 6" would do the trick, even if I allowed for the rotting away of the newspapers at the bottom of the raised bed.
I was right.
Don't believe the man, at least not in the Bay Area, whose soil is underlain, at a very shallow depth, by adobe clay. Maybe in most areas of the world this is not the case, and plants can cast their roots further down, but 6" in a raised bed + a few inches, possibly a foot, more, won't keep carrots, cereal crops (yes, I grew wheat in 2008/09), or other plants with extensive root systems happy.
Make those raised beds 12 inches deep. Ten inches minimum.
So now Bed #1 is happy. More or less. Many valerian seedlings come up, courtesy of my compost, but almost nothing else, unless the birds or the wind have brought seeds there. And Bed #1 was "planted" over foxtail, mallow, blackberry, and oxalis. There is occasional breakthrough of blackberry. But the blackberry has only made its way up the center of one of the cinderblocks. Briefly.
Then, even though I got additional materials through FreeCycle for a "potato tower" (separate topic; a search will bring it up for you) and an additional veggie bed, DH felt--because he actually used his Makita to join said materials together, no doubt--*entitled* to fill those raised beds any old way. This, when he hadn't read anything, dug around in the dirt, or *heaven forfend* listened to me when it came time to fill Beds #2, #3, and, many months later, #4. "No native soil," I said. "Too many weed seeds, and zillions of oxalis bulbs. We can build up these beds with our compost." Because they were in the one small area where, 10 years ago, we had improved the soil and that infamous clay had been broken apart for good. Shallow planting soil, gradually built up, would be fine.
Thus it came to pass that, on the day I knew that we needed to turn the compost to get something into those beds, I looked at them and they were full?!
was weird. This was at the depth of my under/unemployment saga, and I knew that we didn't have $ for anything but the basics. That's fine; I can manage. It's how I grew up, anyway (and we didn't have great stuff like FreeCycle then!). But I wondered--did he go out and BUY all this potting soil???
Then I walked over to the two new beds (Beds #2 and #3) and stuck my hand into the soil to check it out.
...native soil! Absolutely FULL of oxalis bulbs!
And they are still a nightmare, even though the potato tower pretty much discouraged most of the oxalis in Bed #2. It's been over a year since we harvested the famous potatoes. We grew some leafy greens and some root veggies in Bed #2 last year, which means...the oxalis bulbs got sunlight.
And I've been pulling them out. Again.
The only thing that saves the situation is that, when you pull oxalis out of a raised bed, you get the WHOLE root. I've gotten some that are 9 or so inches long below the soil surface, which makes for a pretty l-o-n-g plant.
Bed #3 has had sunlight all along. You know what that means.
But I'm making progress.
By the time we made Bed #4 (I made sure to hold the Makita part of the time on Bed #4
), I had an anti-oxalis/weed plan. Part of my plan worked.
Close planting of leafy greens deprived the oxalis of sunlight. So, in half of the bed, oxalis was severely set back. But, in the other half, I wanted to try tomatoes and a couple of other veggies that come up out of the soil rather than staying so close to it.
On the other hand, be happy you're not dealing with the ones I've already removed (by hand) because they generate spines, thorns, burrs, etc. or are otherwise harmful/toxic to neighborhood cats or my dogs:
--yellow star thistle
Oxalis isn't harmful to dogs, should they take an interest in it. Mine seem to prefer young foxtail grass, but they never eat enough of it to prevent later foxtails. I've been fighting that one for years....
Let me know your plans for filling your raised beds. If you'll be using your own compost, etc. *and* 10" or so of depth, you'll be seeing very few oxalis in those beds.
But if you use native soil...
is how you'll feel. Just so ya know...
Welcome to The Helpful Gardener, and happy gardening. Where in Zone 17 are you? It's a pretty long, skinny zone on the coast.
Sunset Zone 17, USDA Zone 9