Without knowing your zone, it's very difficult tp answer. Fall planting has the advantages of warm soil, usually frequent rains, and far less heat and water stress. In colder zones - 6 and lower, I'd say - the soil may freeze too early for there to be any chance for the roots to establish themselves. Especially In pot grown rhododendrons this is an important issue. Even in warmer zones I'd definitely provide wind protection. Rhodendrons have been known to be blown over, their roots tipped out of the soil bfore they've become established.

Spring planting, once the soil has warmed up, has the advantage of a much longer period during which the plant may establish its roots and become acclaimated to a new environment. Will require more attention to watering, however.

Sorry, I wrote this message twice and forgot to mention my location the 2nd time:

Zone 7 : Long Island, NY

Thank you.

I think a lot would depend on the plant you are installing as well. IMO if you bought a Rhody in the fall that's been sitting out all summer at the mercy of the nursery selling it, you could have problems. FWIW, I would only buy from fresh spring stock and plant there after.

The professionals I know always prefer fall planting since it is more fool-proof because:
There is no stress from top growth
There is little or no concern about watering
In the following spring when there is top growth the roots will be established
There is no heat stress
There is less chance of root disease

But not all is good. In climates with freezing and thawing, root heave is a real problem. One must mulch well and stay vigilant. Desiccation after the ground freezes must be prevented by antidessicant sprays, wind breaks, sun shades, etc.

But spring is even worse. Plants are in active growth and place a lot of demands on the roots when they are the most compromised. Watering is critical, too little causes drought damage and too much can lead to root disease. Too much sun stresses the new leaves. Heat raises the threat of root diseases.

Good luck!

This post was edited by rhodyman on Mon, Nov 4, 13 at 22:41

Propagation and planting methods expert Carl E Whitcomb said in one of his books that the fall planting area was Zone 6 and higher. So that still puts Zone 6 as the borderline area.

For fall planting of hardy kinds.

Since you are in Zone 7, you should be good.

As always with fall planting, if a killer Arctic front blows in right after, you may have to take steps to protect plants just set out - the main idea behind fall planting being advantageous is that the plants take root well planted then. If they are sitting there with no rooting out having taken place yet they won't be able to take the cold as well as if they were connected to the ground.

Planting early enough in the fall that rooting out occurs then is important, there is often little root activity during the winter in cold climates. If you plant something out after the fall root flush is over for that year then most of the advantage of fall planting will have not been captured. With hardy trees and shrubs in general when each specimen pushes out new roots is determined by what the terminal stems buds are doing. The development and maturing of these in fall prompts existing roots to elongate; production of new roots in spring is triggered by the opening of the overwintering terminal stems buds in spring.

I often plant Rhododendrons and other plants in the fall, even though I am colder than the recommended zones. I have very good success with this. Evergreens (conifers and broad-leafed) I plant until mid-October, and deciduous plants I add until mid- or late November. My beds are well-mulched so that they tend not to freeze as early as bare ground, and I live in a river valley, so the water tends to delay fall frosts, so I think my plants have time to get established. Once winter arrives we have good snow cover and not much in the way of freeze-thaw cycles, even in spring. We tend to go from snow to hot in about 6 weeks, so spring planting can be quite stressful on plants here.