I wait with interest to read replies on this. There are already concrete post holes in place here, and I'm wondering how close to them I can plant. And if concrete's not toxic, am thinking of building a hypertufa brick retaining wall.

yes it's fine - other than gradual leaching of small amounts of lime, concrete is really quite inert - just limestone, sand and gravel after all - if concrete weren't acceptable in "organic" gardening, then rock powders and even soil wouldn't be either!

Bill

Here is a link that might be useful: about cement

My home sits on the solid limestone dome of a defunct cement quarry/factory. I hope it's organic.

If you're into hypertufa, you can try making soilcrete instead of concrete. Instead of mixing sand to make the concrete, use soil. Use the same cement/rock/sand/water ratio but substitute the native soil you dug out of the hole for the sand. Instead of being white, it will be soil colored.

I did the same with locust and concrete for my grape trellis. When you set the posts, put 2 or 3 inches of crushed stone or gravel in the bottom of the hole, set the post on it then plumb it by filling around it with concrete. The gravel provides an outlet for moisture "draining" from the post. If you encapsulate the entire post bottom with concrete, moisture (precipitation that the post receives) will puddle in the "concrete cup" and accelerate rotting. An old trick from my days as a commercial fence installer.

Setting fence posts in concrete is permitted and really is often needed. The concrete will aid in stabilizing the fence post and will help distribute the weight that post carries somewhat better than just soil will. As jumla stated put stone, for drainage, in the hole first and then fill around the post with the concrete. At any home inprovement center there will be information, most often good, reliable information will be in brochures not from the sales people of the big box chains.

Although concrete will help stabilize the fence, when the post rots, and it will eventually, it is far more difficult to replace a post embedded in concrete because you have to dig out the huge chunk of concrete too. For this reason, don't use concrete to set posts.

This has turned more into a construction post than an organic post, but althea is correct, all posts will rot. You can take steps to slow the weathering and thus the rot and extend the life of the post. Locust, cedar or chestnut are good choices for posts if you can afford/find them. If you use concrete, finish it so that it slopes away from post to ensure runoff. Puddling were the wood and concrete meet is a sure way to accelerate rot. Cap the post with a piece of wood or metal flashing to eliminate moisture from penetrating the end grain of the post. If you feel ambitious, you can treat the wood every few years with lindseed oil or the like. This would be a lot of extra work for a rancher or farmer with a lot of fencing or corral to maintain but for a few kiwi or grape trellis posts, this should last longer than I will.

grandad could tell you the way to make a post last longest, is to 'plant it' so the part that was the top of the tree is in the ground, butt up :)

Bill

Concrete will actually make wooden posts rot more quickly than posts without concrete. Water gets trapped inside the concrete between the wood and the concrete (or inside the wood), and rots out. The water doesn't drain away. The best method I have seen (and use) to extend the life of wooden posts, is to set them in crushed rock, with no dirt against the posts. That helps the water to drain away, keeping the wood about as dry as you can keep it.

How fast wood will rot when in contact with soil depends on which species it is. Pine will rot fairly quickly while some cedars, redwood, and locust will not. If the concrete is properly used it will help extend the life of even pine.

we have a few hundred posts about 30-y/o set in concrete. many are rotted now & you just put new post between to avoid digging out old concrete. the ground is so soft though that I mix some dry post concrete with the dirt to tamp in. the old 30-Y/O posts were treated, though, not natural wood. What about using pipe?

That's why I use metal posts. They will outperform any wooden post, set in concrete or not.