g'day jim,

top it up, the rain has hastened the settling process.

len

Here is a link that might be useful: lens garden page

Yepper, gardenlen is correnct. All that happened is that the dirt settled. Add more dirt. But do not add any more sand. It is also important to understand that there are no regulations on what a soil company can call top soil. Everytime they scrape two inches of topsoil off they now have a new layer to call top soil. So if you think you are getting the top two inches of top soil you might be right, or you might be getting the top two inches of top soil that was 12 inches down six months ago. I would dismiss any advertisements the seller might make as to additives they put into the soil. I will bet you that if they do add anything it is a little fertilizer and not good organic matter. If they do add organic matter to the soil it will be a lot more expensive than just "top soil" you would normally get. The point to all this is that when you buy dirt from a nursery be sure to realize it is just filler dirt. You need to add your own amendments in order to create the kind of soil you want.

People say that you cannot add too much compost to the garden bed. Well, yes you can. If you add too much then you will begin to get a spongy soil and you actually begin to go back to a soil that will not drain well. Organic material content of the soil should not exceed 10% of the overall volume in the bed. I cannot tell you what 10% looks like, but you can have your soil tested to find out how much organic material you have in the bed as compared to clay material.

Tom

I can see that too much compost would not be good. On the other hand I don't see why adding sand to a clay soil would be a no-no. As it would coarsen the texture. Which leads me to wonder if something like bark would bulk up the soil.

I would not necessarily limit the compost to 10%. That's certainly a rich soil, but you'll notice that commercial potting mixes are almost all organic matter, and stuff can grow like crazy in that.

Adding sand to a clay soil is a potentially rewarding and potentially dangerous practice. The right mix of clay and sand behaves much like concrete when it dries. They say a clay soil would need on the order of 40% sand to get beyond the concrete range. Or, if you keep it very low (I dunno, less than 10%) there isn't enough sand to see the effect. I've seen it go wrong and it's not pretty. Lots of organic matter can mitigate the effects.

Bark is a strong brown which would deplete the soil of nitrogen. I wouldn't mix in any uncomposted woody stuff.

SHRINK .... is what soils with a high organic component do. It's their nature, and the higher the organic component, the greater the shrinkage will be. You CAN slow the rate of shrinkage and help reduce the N immobilization you would experience with other organic materials that break down more quickly by using a material like conifer bark, which is structurally superior to most other organic amendments you're likely to add to a raised bed soil, especially peat.

Here is a picture of the soil in my raised beds at 5 years old:
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It has excellent tilth, it's rich & dark, teaming with soil life, drains and holds water well, and it's very productive.

The soil is comprised (originally) of approx
5 parts partially composted pine bark fines
2 parts sphagnum peat (could also use 1-2 additional part Michigan or reed/sedge peat)
1-3 parts Turface or NAPA floor-dry
1-2 parts builders sand or native topsoil
dolomitic lime
but I could easily have used more sand in this soil.

The soil has around a 70% organic component, and I'm very pleased with it. I did have to compensate for the N immobilization the first year by incorporating 27-3-3 into the top inch, but since then, I haven't had to do much in the way of fertilizer.

Al

When you move any soil and put it someplace else you entrain air in that soil that will, eventually settle out. Same thing happens when you till a soil and the level of that soil is higher than the surrounding area. Then water is added, and water displaces air, and the soil settles, just how much depends on how much air is entrained.
toxcrusadr said "they say" and the they refered to are soil scientists that will tell you that you need to add somewhere between 45 and 70 percent sand to clay to make enough of a difference to be worthwhile, and considerably less organic matter will get the same results. Potting soils are a different substance and are much more that 70 percent organic matter since most are more like 99 percent OM with about 1 percent perlite or vermiculite added for drainage. Keep in mind that amending garden soil with enough organic matter to get that soil over around 10 percent can be very costly since it does take a very large quantity of material to get there. A Lasagna bed can have the same amount of OM as a garden bed and be very close to 100 percent OM while that same material mixed into soil may only be 10 percent of the mix.

Al

Your soil looks great. Compared to my slumped box soil. Looks like mud. And the few plants there, are just sitting. The opposite of healthy. Looking at it the first thought I had is it needs some bulk. Which is why your stuff looks good.

So how long and how do you compost pine bark fines? From the look of the soil it appears to be still somewhat coarse. Which seems to be good. And what is Turface or NAPA floor dry??

Pondering the subject of soil. When looking at dirt and hefting it it is really heavy. Very fine. Odd that water can get through it at all. It seems that capillary action must have a great deal to do with it. I guess that is why containers are so notoriously bad at drainage.

Now my box sits on the ground so it is not really a container. Therefore maybe it doesn't need a coarse soil? As I said pondering.

Technically, it's not that water displaces air in soil that makes it compact. Water evaporates, yet the soil remains compacted. We see water displacing air in sponges every time we wet them, yet they don't compact. The water acts as a lubricant, reducing friction at soil particle contact points. The movement of the water also allows/causes the soil particles to jostle against one another as they change position. The combination of the lubricating quality of the water, and the downward force of gravity allows/causes the soil particles to settle more tightly against one another. This decreases the number of macro-pores large enough to be able to hold water and increases the micro-porosity, which of course increases o/a water retention and how tightly the soil holds water.

Thanks for the kind words, Jim. I'm able to buy partially composted (aged) pine bark from several suppliers within a short radius (15 miles) from my home in a small town, so I don't have to compost them myself. You could actually use an uncomposted bark if it was fine enough. By this, I would say the pieces should be no larger than a dime.

I know some will grouse that the large bark component is certain to cause some degree of N immobilization, and it does, particularly in the first year. As noted, I compensated by adding a high-N fertilizer. 46-0-0 urea might be the way to go, but do your homework & don't over-apply.

Turface is a calcined (baked at high temps) clay with a very irregular shape and very good internal porosity. According to Profile Corp, pound of Turface has about 14 acres of surface area. That is a lot of surface to hold water and lots of ionic attachment sites (for holding nutrients). The floor-dry is a similar product, except that is calcined DE (diatomaceous earth) and it has even greater porosity and a slightly better CEC.

Water movement in raised beds is quite different than in containers. Water is not as apt to perch in raised beds, and surprisingly, water is more apt to ACTUALLY perch in a raised bed above a sandy soil than above a clay soil. Before I catch hang for saying that, let me explain that clay has greater capillary attraction than sand, but it has a slow percolation rate. Water movement downward from raised beds above clay is impeded by the percolation rate, but it isn't technically perched.

You don't need a soil as coarse as an ideal soil would be in a container, but you DO need a soil that doesn't hold water so tightly the soil is anaerobic. If you're thoughtful about how you combine available ingredients, you can come up with a blend that both holds water and drains well. Soo often it's been pointed out to me that you can't have it both ways ..... but you CAN. Using large particles that hold large volumes of water internally provides very good macro-porosity while still ensuring good drainage. The pine bark, Turface, and floor-dry are 3 possible ingredients that will help in the water retention + porosity department. The sand or topsoil + the other organic ingredients provide the additional bulk needed to fill the beds. If you have it, compost is good with the sand/topsoil, or a combination of reed/sedge peat + sphagnum peat.

You'll need to lime this soil, and a single application of a micro-nutrient supplement like Micro-Max for the first year would also be helpful, but regular applications of something like MG 30-10-10 should help to keep the N where it should be and supply any other elements likely to be inadequately present.

Al

Typo correction - first paragraph:

This decreases the number of macro-pores large enough to be able to hold air and increases the micro-porosity, which of course increases o/a water retention and how tightly the soil holds water.

Sorry.

Al