Boxwood is nice but very slow growing. Nandina (heavenly bamboo) works well and has good winter interest with berries and orangey new foliage. Nandina domestica is too tall for your requirements. N. domestica 'Compacta' may be too tall as well (about 4-5'). N. domestica 'Gulf Stream' is about 3-3.5' and very tidy. Do you really mean giant arborvitae? That is a monster - probably grows 3' per year, not 3' total. There are other evergreen shrubs that you might consider, but first determine if you want solid green or the more multi-colored foliage of the Nandina. There are dwarf Pittosporums, Rhaphiolepis umbellata 'Minor', and probably some others as well. I'd not hesitate to get the smaller plants. If they are planted in appropriate soil and given adequate irrigation until the rainy season (and you have to keep checking them if we have dry spells during the winter - you cannot let the root balls dry out and those root balls will be fairly small) they should do just fine and yes, will catch up within a relatively short time.

My backyard abuts a main road. Several times in the last few years, cars drove into my fence causing major damage to it. I asked the town to if I could install a guard rail, or place boulders in front of my fence for protection, they of course disallowed it, however, they suggested that I plant a row of trees to act as a natural guard rail. I need something fast growing that will grow to have a single straight thick trunk like Maple, Oak, Sycamore, etc, etc., but can be planted closely. I would consider planting thuja Green Giants, or other conifer, but I believe that they would have several trunks. I don't care if they are deciduous or coniferous evergreens. I checked several nurseries for Hybrid Poplar, but none sell them. In fact one nurseryman told me what a disaster Poplars can be. The reason I want to plant the trees is to act as a "natural guard rail"

Pierce, just be aware that you will need a male holly for every 5-7 female plants to get berries. Because you will be planting tightly, you might be able to stretch it to one per 10 females. Most of the male forms I know of are shorter growing than the females, in general. You could get around this by using 1-gallon males and planting in the same hole as the females/'Nellie R.Stevens' as you space them out - they can grow up and be available, but are 'hidden' among the mass of the females. I know 15 gal. 'Nellie R. Stevens' are available, but can't speak as to price. While the 'Nellie R. Stevens' are a good hedge plant, if you wanted to mix in another type of tree, the Thuja 'Emerald Green' (a.k.a. 'Emerald Beauty' or 'Smaragd') is another good hedging plant, growing fairly fast to 12-15', and about 3-5' wide. You can fairly easily find 5 gallon plants, at about 4-6' tall - and pay more for them than 1 gal. - so they might be good where you want immediate height. While running bamboos will provide a solid screen once they are established, they will also RUN!! I have pulled out runners that are up to 8' long, and about 6" deep, in the spring. As long as you mow faithfully, you can keep them in check. However, even asphalt won't stop them from coming up - cement MIGHT! You can buy barriers, but you need to make a 3' deep trench for the barrier to be effective, and even then, you will probably have to watch for escapees over the top. Clumping bamboos are much better behaved, and will expand, but stay where you plant them.

You can grow about any hydrangea you want in your zone. For lacecaps, you can try Lady In Red, Kardinal, Blue Wave, or Lanarth White. Those are about the extent of the lacecap macrophylla color spectrum and some of the easiest ones to find. There are some double-flowering ones too but don't get quite as large. Especially, try Wilkerson Mill gardens at hydrangea.com - theyre in GA and would probably be worth the trip to one of their open house sales.