Question about amending soil (probably a dumb one!)

[KT]

The soil here is hard-packed clay. I think I'd need dynamite to plant anything. I know that if I add organic material it will help a lot, but if I add inches of manure or compost, doesn't that change the grade? We had problems with water in our crawl space in the last house we had, and I don't want to raise the grade so that rain runs back into the foundation. If I add the organic material, does it break down over the summer so that the slope of my yard doesn't really change? I hope this makes sense - I don't know if I am making myself clear. I want better soil - but I don't want a wet crawl space.

[fran]

Where are you planning on putting the beds? I don't think you need to be concerned about the grade unless your lot slopes down into the house. If so, I'd look first into regrading the lot, then into any flower beds.

Just breaking up the soil to create a bed changes the grade as you are unpacking a tightly packed bundle. Think of it as opening up something fluffy that was vacuum-sealed - it occupies a lot more space once open! If left alone, it will slowly pack back down, but that may take a few years.

I started with hard-packed clay, too. What I found is that the best time to dig a new bed is in the spring - the ground is at it's softest from all the winter precip. This does require some long-range planning, but saves having to using a pick-ax to break open the soil (been there, done that).

I only amend the soil if planting tender annuals. Bulbs, day lilies, irises go straight into unamended soil that has been completely broken up down to 8" deep. If I need to amend the soil, I just use regular top soil purchased from Lowe's or Home Depot and mix it into the clay. I use a ratio of 1" top soil to 8" clay. The only place I used peat moss instead of top soil was in the rose beds.

HTH.

[David Ross]

My soil is adobe clay. To break it up, I scatter a generous amount of gypsum over it, enough to coat the soil solid white but only about 0.1 inch or less. Then, I lightly sprinkle with water to start dissolving the gypsum into the soil without washing it away. After that, I allow the garden sprinklers continue leaching the gypsum into the soil. After about 2-3 weeks, I can dig without having to scrape the sticky, pasty clay off the spade.

However you do it, once the soil is broken up and organic amendments turned in, water will soak into the soil rather than running off. Unless you get a downpour (or your soil freezes in winter), you should not have to worry about water flowing towards or under your house.

If you are still concerned, you might want to create low landscape berms near enough to the house to be partially under your eaves. Not only would these divert water, but they also are good for plants that are sensitive to poor drainage.

[Phisherman]

Hard-packed clay is actually a good thing next to the foundation, provided the grade slopes away from the house. Watch carefully after a rainstorm to see where the water puddles. I love gardening, but the house foundation has a high priority. You can leave a couple feet untouched next to the foundation and work your planting beds from there. I do not allow any plant to touch the house and the space against the foundation allows for a quick and easy monthly termite inspection by the home owner.

[simy1]

If you add three inches of manure, it will change the soil level by approximately half an inch after earthworms incorporate it into the soil. The other posters gave good advice, but one other thing you can do if you want to break the soil further in is to plant fava beans for the season (after having spread the compost). If they cannot break it, no plant can. There are other plants, all with strong taproots, that will do the same.

[David Bockman]

"KT" wrote in news: [e-mail]:

You can simply top-dress with any good organic material, and over time it will leach downwards and really improve the soil structure. Scratching the hardpan surface first will help start the process, as would doing something like core aeration (as is done with turf). In very compacted conditions, I suppose it would be possible for thickly laid top dressing to wash away in a hard rainstorm (as rainwater sheets across the hard surface), in which case you would need to rethink how you're going about soil improvement.

As to how quickly organic material is leached into and incorporated into soil structure, there are so many unknown factors it would be foolish to predict.

[David Ross]

The only substances that will leach into the soil are those that will dissolve. Organic materials containing any residue of cellulose will not dissolve or leach.

They will gradually be incorporated into the soil by earthworms and other non-microscopic fauna. They will also be incorporated by tilling and the digging done during planting.

If you merely top-dress with compost, manure, peat, or other organic matter without tilling, you will create a distinct layer. Water might have trouble penetrating the interface between the layers. The roots of small plants started in the organic layer might not grow past that interface, leaving them shallow-rooted (vulnerable to drying and even cooking in the summer). The result could be worse than not top-dressing at all.