Top Dressing: When and How

Question

I recently started composting, and I was reading about top-dressing. Two questions I have about top-dressing are:

• Is there a maximum to it? Most of my reading suggests up to once a year max.
• Do I really need to rake it under the grass? Some sites suggest leaving it on your grass (it'll disappear by itself), some suggest raking it until it goes under the soil.

If you're wondering, my backyard area has quite a few weeds (hoping to eliminate most of them), a few small bare patches, and a few areas of yellow/dead grass. I'm aiming to eliminate most of the weeds and get a consistent, thicker grass for this year; maybe some vegetables next year.

Edit: I live in a place where we get cold winters (-20C and under) and hot summers (up to 30C or so).

Answer 1

• When: twice a year, spring and fall for areas where there is a cold winter
• how much: you should be able to still see the grass. complete coverage could be counter productive if the grass cannot grow fast enough to reach the light. Whether it will or not depends on your zone and health of grass and soil
• raking helps but is not necessary unless you put a lot on
• the first part of top dressing is adding more grass seed. By seeding twice a year the lawn can stay thick with less room for weeds. Fall seeding works well as the seed will not germinate till spring when there should be more moisture.

Answer 2

I don't know the "right" answer, but I'll tell you what I've done.

The Lawn

I'm in a similar climate, temperature-wise. My lawn is pretty pathetic; I don't put much effort into it.

I top dress around my apple trees in the spring and fall with about 1" of composted horse manure. I don't bother to rake it in -- some mulch on the surface is nice to have there. This spring I had some compost left over in the wheelbarrow so I spread it around on a nearby patch of lawn -- I did rake that in.

The grass in that ring around the trees is thick and green. The grass where I raked the extra compost is greener than the rest of the lawn, but less so than where I piled it thick around the trees. Actually, there's a strip of lawn "downstream" from one tree where the rain runs off that seems to be benefiting from the runoff from that inch of compost.

The Vegetable Garden

Last year I had two patches of corn in my garden. I fed the first patch every couple of weeks with liquid fish fertilizer. I gave the second patch a top dressing of 1-2" of composted horse manure when it was maybe 2' tall. The first patch did ok; the plants struggled a little bit but I got a decent yield. The second patch did well; the plants were strong and had nice green leaves, though I'm not sure the yield was any higher.

Part of the veg garden was new, and the soil wasn't built-up yet. I had squash planted there that weren't thriving. I tried top dressing with about 2" of manure on half the plants and dried blood on the others. The plants treated with blood responded much faster. Unfortunately I can't say much about yield, which was poor. An infestation of squash beetles and powdery mildew didn't help. Part of the lesson learned is that "fixing" with top dressing doesn't always work: weak plants invite pests and disease. (The volunteer pumpkins 30' away growing out of the compost pile -- very well fed from the start! -- were relatively unaffected by the beetles and powdery mildew.)

The Horse Pasture

I'm building soil in a sloping area of would-be horse pasture that's got very poor soil. Think of it as a large lawn. As an experiment last fall, I dumped several 1' high by 2-3' wide windrows of compost along contour lines on the slope. Not surprisingly, the grass below those piles grows better than anywhere else -- the nutrients flowing out of the windrows when it rains feeds everything downhill. Obviously, though, nothing grows directly under those piles -- not necessarily what you want to have on your lawn, though I'm tempted to do this and plant some flowers into the pile.