Establishing New Garden Beds

ETA: Sorry, this was somehow mistakenly published in the Jan 2011 posts!

Establishing a new garden is hard work, and I seem to convince myself to do it in at least one spot every year.  Here's what I've learned so far.


Gardening books often suggest double-digging to establish new garden beds, but I have found this to be a terrible idea around here.  The topsoil here is really only about 6-9 inches deep, with the subsoil consisting of extremely fine clay with large rocks buried in it.  Theoretically, when you double-dig you lift the top foot of soil up, loosen the underlying layer of soil with a large garden fork, and then put the top layer of soil back in place, adding soil amendments and air in the process.  The trouble is, if you try to do that in a location with less than a foot of topsoil, you end up mixing subsoil into your topsoil: in my case large, rock-like clumps of clay.  Also, after the first good rain the soil surface settles down into a cement-like, impermeable layer that just can't be good for plants.  There is a spot in our front flower bed where I double-dug my very first garden, mixing in compost and bagged garden soil; I only grew vegetables in this spot for one year, but four years later the soil in that section is still noticeably poorer (and lower, from me subsequently picking out those clay rocks) than in the rest of the bed. 

I also tried the lasagna garden method with the big backyard garden bed I added in 2010 (see Not Breaking Ground on the New Garden), laying down cardboard and covering it with 6-8 inches of compost I got from the city.  This worked extremely well for keeping the weeds down, but the soil and compost layers were still not well-mixed a year later when I dug a soil sample.  Proponents of the lasagna method claim that worms will slowly incorporate the new materials into the soil beneath.  I did find evidence of lots of worm activity below the cardboard (see Happy Pooping Wormies), but none above during that entire first year.  Maybe I messed it up by using finished compost instead of things like grass clippings and shredded leaves, but I was sufficiently discouraged by the results that I decided to just go back to single-digging.  Also, lasagna gardening is supposed to be less physically demanding than methods that require digging into the soil, but by the time I moved and spread and leveled all that compost I really didn't find this claim to be true, either.

My current preferred method for establishing a new garden bed is to add bagged soil, fertilizer, and vermiculite to the top of the bed, then mix it into the top layer of soil with a shovel, and level it and break up any clumps with a metal rake.  Then, before I plant it, I try to firm it down a bit.  Most books I've ever read say you shouldn't walk on the soil or press on it at all, but I do it anyway because I think it helps prevent that cement I was talking about earlier.  (When the soil is too loose the top layer gets dried out much faster, then the clay particles get stuck together, making the surface very impermeable and difficult to re-wet.  That's my theory, anyway.)  Last spring I also used garden sulfur in my community garden plot beds, which many sources suggest helps break up clay soils, though I can't tell if it did any good or not. I'll probably use it again.

Hmmm, I wonder what I'll think of this method in a couple years?