Do not use landscape fabric or black plastic in a garden. It's evil stuff. Tree roots and other roots go right through it and create a mess that will take months of work to correct later on. If you are going to use a barrier use newspaper (5 or 6 layers thick) or cardboard. Those materials will eventually break down, but it will give your hostas a head start.

There are plenty of threads here on tree root invasion. Some trees (maples) are more invasive than others. If you are planting beneath invasive trees like maples you should consider planting in pots in the ground or in spin out bags. If you are using Oaks for shade then you can go ahead and plant underneath them. Don't pile up soil around a tree trunk, it will eventually kill a tree, any tree, some just faster than others.

I would give the tree some breathing room and then layer a newspaper barrier under about 8 inches of compost and that should give your hostas a good start. As for watering, you have to understand that Hostas come from areas where they get 60 inches of water a year. Generally speaking, Hostas that receive supplementary water will grow faster and larger than those that don't. That doesn't mean you can't grow without supplementary water, many on this forum do that, and their hostas are beautiful. But they do better with more water.

Remember they're Hostas and will grow in many different conditions (including on Ken's driveway), so just go ahead and plant them where you want. Just don't use the evil landscape fabric and plastic.

Steve

Hosta roots don't really go that deep.

12 inches is probably going to be enough. However, you want something more substantial than just compost. As compost breaks down further, your soil level is going to shrink.

Also, be concerned about whether you might smother the tree. Most tree experts would suggest you do not pile a bunch of soil on top of established tree roots. You might have seen that you should actually plant a tree a few inches above ground (at the trunk... so that the first root flare is exposed). By piling soil on top of the roots, you're basically burying it deeper than it should be in the first place.

There will be others here who will say, "it's not an issue, I planted a raised bed around my ______ tree". I'm not disputing that it can be done.... I'm only offering that many experts suggest it should not be done.

Also consider this. You like this tree, right? By using landscape fabric and/or plastic, you're preventing some/all water from reaching the tree roots in that area. No matter how "permeable" the stuff claims to be, it's still not going to allow all the water to reach the roots.

Now, all that said, this assumes you still WANT to do this project. As was said above, most of us who've been there done that will BEG you to not use landscape fabric. It's AWFUL. WHEN you want to remove it, and trust me, you WILL want to remove it cuz it is really a gardener's nightmare, you will spout ALL KINDS of profanities. Just search this forum. You'll have a hard time finding anyone who likes it.

thanks for your heartfelt advice!- I dislike plastic fabric too- but I was looking at this thing
http://www.texel.ca/html/en/horticulture/products/controle_racinaire/texr_propagation.php

So let me explain how the area looks -
area1:
its a rectangle about 80 feet x 50 feet or so with 2 big pine trees at 20 feet and 60 feet on one edge. The trees are big and their drip line is about 10-15 feet or so (my numbers ...need to verify) My plan was to do something like this

[IMG]http://i54.tinypic.com/1971gn.jpg[/IMG]

maybe a better idea ?

Here is a link that might be useful: my plan

Give me a second to pass on 2 horror stories about plastic as ground cover. I won't go into individual details because they both came out the same. I had been asked to help with two garden beds where nothing planted survived more than a couple of weeks. The soil was covered as you have described with the bed built up on top of the plastic. The plastic was not visible until I took a shovel and dug a test hole. As soon as I penetrated the plastic I knew the problem and tore the bed up and ripped out the plastic.

The soil under it was so rancid I almost couldn't take it. The problem was no oxygen in the soil and all of the organic was being consumed by the bad bacteria that survive without oxygen. This was worse than the worse sour drain I have ever had to clean. The odor was largely from methane and hydrogen sulfide gases, both of which are toxic to plant life. I neutralized the soil and turned it to get oxygen into it and it still took weeks before it would support desireable life.

In new fish tanks it takes about 6 weeks to establish a good culture of nitrifying bacteria. If you load fish into the tanks before this the waste is not consumed and the fish die from ammonia poisoning: a byproduct of incomplete decomposition. I guess the same is true in dirt. Our plants need these around their roots to be able to use the nutrients available in the soil.

Les

Ani,

The spin out fabric that you linked to will work fine. I've used it in the bag format under maple trees and had success. But it's very expensive, especially the amount you would need to cover the size beds you are thinking of. If you use newspaper or cardboard, that will give your Hosta a head start on those roots and allow them to compete. Just don't pile up the soil next to the trunks of your Pines. Give them some breathing room and then start creating your beds. Your plan looks great.

Steve

it wont.. do not burying impervious plastic.. or you might kill the trees above..

tree roots need oxygen as much as water.. and once you cut that off.. things below.. like roots.. die ...

ken

ok- wont go with plastiic- I found some organic ground cover thingie made of corn or some such- what about that ?

I dont hve acess to that much cardboard! and my compost is here!!! looks beautifyl
Steve thanks for the encouragement :)

The spin out fabric I found also has spin out paint. that I read about is not aht expensive less that a 100 bucks for a gallon. I can get by with that much I think... I just cant afford to have the fabric shipped- heavy

Which forum here would know more about spin out ? I can post there...
thanks much everybody!

search found this......

Paul

Here is a link that might be useful: Search : spin out