asparagus in raised beds. How deep?

[Rhiannon Feimorgan]

I have a big problem with mint and thistle in most of my yard. I've tried everything from direct applications of vinegar to smothering the whole garden area with black plastic for a year. For the most part I can keep on top of it by periodically turning over and digging through my garden beds and removing as much of the risomes as I can. This has been hard to do in perennial beds like my asparagus patch. My asparagus in particular seems to be really held back by this constant disturbance of it's root structure.

So my plan is to build raised beds with a barrier on the bottom that will let water through but not roots. Hopefully this will keep the mint and thistle out. I'm not sure how deep asparagus roots need to go. I'm thinking 2 feet of dirt in a 4ft by 12ft bed would be good enough if it's good soil with lot's of compost but I'm not sure. I'm doing the same with my strawberries but I'm not as worried with them as they are fairly shallow rooted. Eventually I want my whole garden in raised beds but I can't shell out for all the materials at once so I'm going to do a few at a time over several years.

Anyone growing asparagus in raised beds?

[insahmniak]

No, I am not growing asparagus in a box. But I hope you'll let me chime in...

I'm not familiar with mint and thistle rhizomes. Are they deep and long? Can you dig out and remove/screen the dirt that will sit under the box, maybe six or 8 inches or so? Replace with what you know is clean. Put your impermeable to roots material down and then then the box and then fill it? Then, in the very center of the box cut an x or hole in the fabric where the asparagus can dive. If you work hard to deplete the rhizomes of the plants surrounding the box they may not have a chance to migrate under the box all the way to the center, then back up to earth. That would be an amazing journey, though I'm sure there's some weed out there that is capable of it.

I share your pain. Ours is of the quackgrass variety. The guy who lived in the house before we bought it hauled in 40 bales of straw when he built it as a way to build soil, rather than sodding it. Commendable intent, but it spread quackgrass all over the backyard. We tried pulling it. Got worse. Then we tried solarizing it. Nice in theory but it didn't work out for us. I've recently tried straight vinegar and I did see damage, but know it's only surface damage. Our current approach is to whack the tops off down to the dirt, rake up the debris and spray all baby shoots with vinegar as soon as they come up until the rhizomes are depleted. Depletion: that's our latest plan.

We also really like working with raised beds but are fearful the little shoots will come up though the bottoms and we'll be growing quackgrass in our newly-purchased soil. That would throw me over the edge. The approach we decided on is to use the whack/vinegar/deplete method all around the boxes as long as necessary, and the boxes are getting lined underneath with very heavy duty cardboard which we were able to source from an appliance delivery place. I'm thinking of actually stapling them to the bottom to make sure they stay in place and make a fairly tight seal. Over time I'm hoping we win the quackgrass war, the cardboard breaks down, and we have wonderful soil layers in the boxes. I have an asparagus plant that was overtaken by the quackgrass and I tried to separate it but I'm actually just going to pitch it. I simply can't take a chance that there is some fraction of a rhizome in that huge root system.

[Rhiannon Feimorgan]

Well last year I dug out and screened a bed, covered the whole thing with black plastic and then cut holes in the plastic to plant tomatoes, peppers, broccoli, cauliflower and cabbage. The holes we all at least three feet from the edge of the bed and by the end of the season they all had mint growing up through them and a few had thistle. The thistle doesn't seem to grow as fast but the rysomes are so tough and wiry that they seem to be able to grow through almost anything. I've seen them poke up through landscaping cloth.

[insahmniak]

Just curious - has the mint gone to seed in the yard? Corn gluten is supposedly a good pre-emergent. You probably know that, though. Sounds like you've been at this for some time.

That's discouraging about the mint coming up even after you screened the soil and planted inside such a huge margin. What material are you considering using on the bottom of the boxes?

[Rhiannon Feimorgan]

I have some pieces of old wool carpet that I'm going to attach to the bottom of the box. I figure it will take some time for it to break down but it will be ultimately biodegradable. Hopefully by the time it broken down I'll have the situation under better control in the rest of the garden. I'm looking at a long term project of changing the nutrient profile of the soil so that it is no longer as hospitable to the weeds. I'm not sure how this will work with the mint but the thistle apparently doesn't like soil thats too rich. It's a "first invader" plant. From what I've read, if I can improve the soil enough the problem will take care of itself but it's going to take years.


Sigh, there is very little instant gratification in gardening.

[Literate]

Originally Posted by Rhiannon Feimorgan

Sigh, there is very little instant gratification in gardening.

Quoted for truth, man. Quoted for truth.

I have asparagus in a raised bed. Ours is 10x10 by 10 inches or so, but no barrier at the bottom. Only one row is asparagus. I think this is our third year, so I'm expecting a big harvest. Last year was pretty decent. Mmmm. Can't wait.

In summary, your plan sounds good!