1) True cedars (Cedrus species) are not considered allelopathic. 2) as far away from the dripline of the tree as you can tolerate......even then you will be trying to outcompete tree roots and guess who will win? 3) Yes there are but they constitute a rather short list. Look for plants for dry shade or just very drought tolerant plants if the tree is limbed up high. DT groundcovers are your best choice - they tend to be surface rooted so can subsist on minimal soil and often compete well with big conifers. Plant any larger shrubs - and again, these should be very drought tolerant species - away from the base of the tree. And be sure to provide extra water and TLC for the first few growing seasons - drought tolerance is by no means immediate!! 4) You cannot plant much of anything within the root spread of a large conifer without disturbing roots. Make it easier on yourself and the new plants by starting small....like 4" pots for GC's and 1G for any shrubs. Easier to dig holes for, easier to get established, more likely to complete well with the tree. Be patient - plants grow. Here is a link that might be useful: DT groundcovers

I have seen curled branches many times on deodaras when they come out of the nurseries. A lot of times it was because they were grown in a confined space so the branches curl around the tree. If this is the case the branches may or may not return to their full outward hang depending on how long it has been confined and how thick the branch has become. What I have done in a few of these cases is similar to what guys do when they are working on a bonsai tree.....I get heavy guage wire from Home Depot and cut it in pieces about 1 1/2 times the length of the branch. Then I wrap it loosley around the branch starting from the inside near the trunk and working outward. When you get out to any where near the end of the branch snip the remaining wire off. Now you can bend the branch into whatever shape you like and the heavy guage copper will be stiff enough wrapped around the branch, to hold it in the shape you bend it. You may have to leave it for a year or two to re-train it and make sure it will hold that new form, but it's worth it. And you cannot do this on mature thick branches.....only younger ones say smaller than an inch caliper. The thicker and older they are the greater the chance you will split the branch. mark

It is raining right now, but when it stops, I will take a pic so you can see what kind of cedar it is. It does not seem to have much sap at all, I do not know if it is because of its type or not. I have actually had large potted above ground hostas under this tree for several years. They do not even get winter protection, and they have survived with no loses. But I have always had not too special types there. If I make the bed, I want to put some nice ones there. Like I said, they would be in their own large pots in the ground, so I think it would be hard for the tree roots to disturb the hostas. Since it is a raised bed, I was also going to lay down that black garden cloth (forget the real name of it) for added protection from root intrusion. So between them being in pots and the cloth under the bed, I think it should be ok. I am just at a loss for shade now and have many homeless hostas. And my addiction will not allow me to stop buying so I am desparate to find more shaded places! LOL! I live on a lake, and where it is not bulk-headed, is nice shade with trees that go up to the water line. I would LOVE to put hostas all through there,it would look so natural and beautiful. However, the ground there is too rocky and hard to dig through because of the waterline. So I cannot even really dig down enough to put pots in the ground. I could just put them in pots above ground and have them like that, but when it comes winter, I do not know how they would handle being in pots above ground. However, I have many hostas in pots that stay above ground all year long, and come back every year. Out of all of these years, I think I have only lost 1 or 2 in pots above ground. SO it probably can work. I have lost so much shade over the years here. Not only to storms, but for some reason, when trees here get to a certain age, they start to rot from the middle out, I assume because they are taking in too much water from the lake. I learned this the hard way when a 75 foot pine fell out of nowhere! It missed the house by a foot! I also just recently had to cut a nice huge Oak for the same reason. It was actually leaning towards the house, and the middle was rotting. Lost 3 oaks that way. Well, enough rambling. I will take pics when it stops raining so you can see the cedar. Thanks!

hairmetal: I wouldn't rule out "decline or removal due to non-hardiness related factors" as the reason for so few large cedars in the DC area. For example I remember a big one on Trap Rd. or thereabouts in Vienna, VA. At some point in the mid to late 00s, the last time I drove through that part of Fairfax County, I noticed it had been cut down. It was along the road, by a house that was close to the road, and I suspect either the utility or the owner decided it was just dominating the lot and the power lines too much. As I've noted about hollies, large, dark trees for some reason scare some homeowners. Elsewhere there was a huge Cedar of the Atlas or Lebanon pursuasion...I could not be sure. It's the one I posted a picture of a while ago. It seems ot have some kind of foliar disease or decline. Maybe caused by soil compaction, herbicide damage or whatnot. I was aware of that tree and it was definitely not damaged in 1994, cause I did landscaping the following summer and I remember seeing it. But yes, the winters of the late 70s, mid 80s and 1994 could have weeded some more tender strains of deodara out.