Two possibilities I can see. First, and most likely is that, much like many varieties of peat moss, compost that has been allowed to get very dry is well known to develop a hydrophobic surface. The other possibility is that it was contaminated with an oil or something similar. If it was the latter, you would probably be able to detect it by odor, but not necessarily.

If it developed the hydrophobicity because it had at some point become dry then with a bit of persistence it can be rewetted. You can probably speed up the rewetting by using an agricultural surfactant (i.e., a spreader). Ordinary dishwashing detergent will work, but it can cause damage to plants and wipe out all kinds of desirable microorganisms at the same time. Turing the compost into soil would also help.

If you're using it as a top dressing or mulch, just be sure to check that indeed water is infiltrating the soil beneath the compost and it's not developing a hydrophobic interface between the two.

The drying is new to me but your mention of peat seems to remind me of once seeing a similar thing with a bale of peat. Somewhat reasuring that it might be the result of getting too dry(can't emagine how that happened in Texas)rather than containing used tractor engine oil.
I used some in large containers over 3 months ago which continue to drain then dry out quicker than i am acustom to. Which makes me ask once again about the water that drains from the containers and will likewise drain and be reused if I try wetting the compost in barrels. Early on when I was seening a lot of my rain water wasted through drainage from containers,I asked opinions on throwing mollasses in the water then airating 12 to 24 hours before reuseing it to water plants. I was lead to believe the "leachate"is toxic wherther reused as is or airated. I'm back to a similar situation with this compost. What if I put the compost in a barrel and water it as if it were a container plant,recycling the water/leachate through the compost? I am curious ;
If the compost will rewet and act differently if the problem is indeed hydrophobic but continue repeling water if it's contaminated

Will the drained liquid become unfit if recirculated through the compost 2 to 4 times over a period of 4 or 5 days. My supply of rain water is runnig low contending with triple digits so I need to water something or use it for soil sterilizer in a fence line.

I am torn between nameing this stuff "Box Of Chocolate" or "Mad Dog".

I've never head of recycling compost leachate back into the compost, but that's because if it is kept adequately moist it usually doesn't drain much until it's saturated. However, I don't see any problem with it. If it came out of the compost/soil, why can't it go right back in?

I think a more expedient approach would be to contain it, then periodically moisten and turn it, as if it were a somewhat dry pile, sneaking up on an evenly moist but not wet compost. The issue is, if it drains really well, it will run off to the bottom, so you need to be able to stir/toss from the bottom.

For what you already spread as mulch, you might try watering with an agricultural spreading agent added (surfactant safe for plants, etc). That should help get the wetting process going sooner rather than later, then try to keep it somewhat moist afterwards.

Not only does it occur with peat moss, but it is a common problem with many mulches that are allowed to dry out if they are too dense or finely ground.

This post was edited by TXEB on Fri, Aug 2, 13 at 11:53

I've had this happen with potting mixes too, especially if stored in a bin over winter in the garage where it could dry out completely. Potting mix is often just peat moss and compost. It's just how organic matter acts when it's very dry. I don't think there's anything wrong with your compost.

Thanks for the good advice. I just love it when there's a "two birds with one stone"outcome. I posted earlier this week seeking best way to store compost I produce so I can take it to a dear container gardening friend who can't undertake composting due to HOA rules. I have always used compost as soon as it's ready,some even sooner i I need mulch. I now know that material destined for my friend is better left in a bin and moistened rather than bagged up. I always suspected store bought material was only better than nothing,and all this reinforces that feeling.

Just like Peat Moss, or any other form of organic matter that is allowed to get quite dry, compost that has been allowed to dry out can become hydrophobic, water repelling. All that is needed is patience and a place that the compost can soak in the water that is slowly applied.
Even soil that has been allowed to become quite dry can be hydrophobic.

I believe I heard that somewhere. Thanks for reminding me Kimmsr

Sometime when I want some compost the stuff in the bin is rather clumpy. I take out some with my compost fork and pitch it out onto the grass. Then I start the push mower with bagger attached, and run it over. The result is a fine material, quite fluffy.

All you have to do is put 1 teaspoonful of dishwashing liquid in a gallon of water and sprinkle it over the compost.

That breaks the surface tension - it's a wetting agent - and then water can soak in.