If you've never constructed a retaining wall of any kind before, then it might be best to deal with materials that are easy to work with. As a poster above noted, flatter stones, rather than rounded stones, would be relatively easy to deal with, but even there you might want to consult with the folks you buy them from. Look around your area at the various nurseries and stone yards where stone is available. Usually its sold on pallets and can be delivered (for an additional fee, of course). As another poster indicated, type of stone is a choice you'll have to make on your own with regard to look and color. The right or wrong type of stone is difficult to specify on an internet setting, not knowing where you live or what types of stone might be available in your area. Stone type should be based on look you want, color you like, relative ease to work with, and weight of the individual stones (remember you have to pick these things up and place them and turn them and move them around until they fit just where you want them. With regard to the weeps, you really only need weeps in a stone wall if you're going to mortar the stones together. If the wall will be dry set, then the spaces between the stone will be sufficient to allow ground water to drain through the wall. If you are going to set the stones in mortar, then you will have to set weeps between the stones. But on a 15 foot wall, you should need no more than 2, spaced as equally as you can make them, about 4-6 inches above the grade on the low side of the wall. The gravel behind the wall is very important, as well as under the first layer of stones. Six inch minimum (compacted) under the first layer, and 6 inch minimum behind the wall. A full foot of gravel behind the wall would be better, and carry that gravel up to about 6 inches below the final grade behind the wall. As for the existing wall, if you're going to go to the effort to replace it, then remove it completely. You might even be able to salvage some of the old blocks for reuse elsewhere.

Thanks all. Note that in addition to being a gardener, I love birds and in fact try to attract them to my yard via feeders, birdbaths etc. So I would never want to wantonly remove a haven for birds. However, I also understand the value of trees, which are unfortunately grossly under-appreciated, and their contributions grossly misunderstood, by most people in NYC. So this is why if I think a tree is at risk, that I should do what I can to save it. I also read a terrific book recently, "Bringing Nature Home: How Native Plants Sustain Wildlife in our Gardens", and it talked about this very thing...how non-native plants (such as English Ivy) can dessimate native plants/trees. As for those who mentioned that sometimes the ivy itself helps to anchor a tree, well I'd imagine that if a tree needs that kind of help in keeping upright, chances are it wasn't much longer for this world to begin with. But I'd suspect that in many instances, it's a case of ivy simply growing up and eventually masking an entirely healthy tree, and that eventually the ivy will block out its ability to take in sun. So at this point I still plan to cut as much of the ivy as I can without damaging the tree bark itself. Tx!

Asiatics will probably grow as long as they get sun, hybrid lilies are pretty tough. But they will grow better if you amend the soil when you plant them. Since they should be planted deep (8"-10") this is a good time to throw in a bag(s) of leaf mold, top soil, compost, etc., to help them out. Mulch a lot also. That will help keep the soil cool and moist, and would be especially helpful in dry hot conditions. At least rot won't be a worry!! -Helen

The Spanman Calculator has me confused with 1 or 2 row/s bridging? My assumption is that load is always shared across 2 Purlin's. The load should be the same for every Purlin in System. Given the weight is kg/m2 and divided equally with each Purlin, 1 or 2 row bridging should not make any difference, should be the same thing?