Build a healthy garden over your lawn without breaking your back

After years of trial and error, I've finally developed a method for turning lawn into a lush garden with minimal effort. I only exert calories when it will truly benefit my plants. And I'm willing to wait an extra season for the soil to mature, rather than doing something radical like replacing all the dirt. But at the same time, I'm not willing to compromise the health of my soil. My methods are developed for the Pacific Northwest. In other areas, your soil type or climate might require some variations on this method. But if I moved somewhere else, I'd try this first, then tweak it as required.

1. Build a border. Do it right on top of your lawn, using galvanized Simpson framing straps to tie the corners together. I recommend using untreated 2x6 (or 4x6) lumber and just replacing it every decade or so. 2x8 is even better, as it allows you to add more topsoil. In a later post I'll explain the drawbacks associated with different kinds of treated lumber. You can, of course, garden without a wood border. But if you do, you need to scrape up the grass along the outer 12 inches of the perimeter. Bury the removed grass upside down under your newspaper - it's valuable organic material.
2. Apply a double helping of complete organic fertilizer. That's right - apply it at 2x the rate recommended on package. This is an expensive and important item. If you live in a rainy area, add agricultural lime too (from a garden store, not a construction center).
3. Lay down a couple layers of newspaper or cardboard. This step is optional but helps kill the grass more quickly.
4. Add at least four inches of a good topsoil mix. Never accept free soil - unless you know it's rich loamy stuff scraped off the few inches of a beautiful prairie right before the cul-de-sac went in. I always use my garden center's "premium three-way topsoil mix," a mixture of sand, compost, and loam. Sand contributes drainage, compost binds and slowly releases nutrients, and loam contributes minerals and sometimes drought tolerance, depending on content.
5. Grow a full season of cover crop. I include a variety of seeds in the mix. I like using alfalfa, some kind of vetch, fava beans, and fodder radish (fodder as in food for livestock). Vetches and fava beans are legumes, so they "fix" nitrogen in the soil. Books have been written on this process. But basically symbiotic bacteria living in colonies on legume roots pull nitrogen out of the air and bind it up in the plant. What the bacteria get out of the deal I don't know. Fodder radishes - big daikon radishes will work too - are quick to germinate and grow a huge taproot. Later, you chop them off at the top, allowing the taproots to remain in place. Alfalfa produces tons of green matter.
6. Harvest your crop, and return it to the soil. After the radishes have grown say three feet high, you're ready for your first harvest. But this time around, all your harvest goes back into the garden. If you don't have a compost bin, bury the green material in ditches in the garden, letting the roots rot in place. Some will resprout. The more you chop them up the less resprouting later.
7. Two weeks later, you're ready to plant. Letting the bed lie fallow for two weeks gives the greens time to decompose a little.

A new garden populated with cover crops and a few ornamental shrubs.

Here's the science behind the method:

• Other layered garden systems (such as the "lasagna method") typically suffer the first few years before the different layers have "mixed." Roots from tomato plants, for example, thrive in the fluffy stuff on top but can't penetrate the harder soil below your old lawn. Therefore, these gardens suffer from the slightest drought during the first year or two. That problem is reduced using my method. Cover crops send roots deep into the subsoil, breaking down the barriers between layers. Fibrous roots rich in nitrogen from the legumes, fleshy taproots from the radishes. When the roots rot, they form food sources and transportation corridors for worms. After the worms digest them, your tomatoes will send their own roots down these rich veins of worm doo-doo and on into the subsoil, where water hides during summer droughts. The taproots also pull up deep minerals from your subsoil, bringing them to the surface.
• Nitrogen-rich leaves buried in garden ditches will give their accumulated nitrogen back to the soil - and to your future garden plants.
• The fertilizer not only enriches the subsoil with minerals; it also provides fuel for microbes that help break down the grass and newspaper.

One of the biggest drawbacks of this method is that not everyone thinks cover crops are beautiful. If your intended product is a flower garden, many people will think they look weedy during the cover crop phase. But these crops have their own beauty when you look closely:

A blooming fodder radish.

Is your climate different? Here are some ways my climate impacts this process: Frequent spring rain speeds decomposition of buried greens, clay subsoil binds and keeps nutrients nearby when rain leaches them from the topsoil. If your soil is very sandy, you need to be extra careful never to leave your garden uncovered - beds should have garden plants, cover crops, mulch, or synthetic row cover at all times - or the nutrients will just wash down the drain.

Using this method, you'll find your soil rich with worms and the biological activity necessary for your plants to thrive. Other methods will allow you to garden immediately, but you'll do more work and your plants will need more frequent attention. I sneak cover crops in the bare nooks and crannies in my garden because I've come to love their inconspicuous flowers, disease resistance, and biological value.

Happy gardening!