Rhododendrons/azaleas and hydrangeas require somewhat similar things. They both like moist soil, not wet. In the South, they have to have part shade but some can grow in full sun on the Northeast. Some can grow well in shaded areas. However, more sun stimulates more flowering, which is a good thing (unfortunately, it may also trigger lacebug infestations in rhododendrons).
Both do not require fertilizers in large amounts like roses do. Established rhodies require no fertilizer at all; they feed off the decomposing mulch. If your soil is defficient in minerals, apply a 6-10-4 fertilizer like Holly-tone to the soil after blooming but before July. Hydrangeas require a fertilizer application once a year in the northern half of the country (June) and twice in the lower half of the country (May and July). Nothing complicated mind you. Say 1/2 cup to 1 cup of manure or cottonseed meal. One important fertilizer difference: rhodies should not be fed aluminum phosphate as it can be fatal to rhosides/azaleas in large quantities. A/S does not cause problems for hydrangeas; this amendment is used by some to make colored hydrangea blooms turn from pink to purple or blue.
They both require acidic soil and will tolerate some alkalinity but not that much. Best acidic soil for rhodies is around the range of 4.5 to 6 in the pH Scale. Some hydrangeas will not react much to alkaline soils until they hit values well above neutral (7). Colored blooms in hydrangeas will change along with the soil pH but rhodies' blooms do not. Rhodie blooms last about 2 weeks (approx) while hydrangea blooms stay on thru Fall or even repeat on some varieties.
They both also require well-draining soil but here is where hydrangeas (Oakleafs excluded) will outperform. Rhodies will develop root rot if left in standing water for long periods of time while hydrangeas (Oakleafs excluded) can tolerate clayish soil some more. This is due to the types of roots. Rhodies have very tiny fibrous roots that only grow in the top 4" mostly while hydrangeas develop more extensive root systems. But do not misunderstand me, hydrangeas are not impervious to root rot.
Use the finger method if you are uncertain as to when to water. Insert a finger into the soil to a depth of 4" and see how it feels. If it feels dry or almost dry then water 1 gallon of water and record this in a wall calendar. If it feels moist, do nothing. If it feels wet, determine if any action is needed to correct this. After using the finger method for 2 weeks or so, observe how many days apart you watered. Set the sprinkler or drip irrigation to water 1 gallon of water on the same frequency. If the temperatures change 10-15 degrees up or down, re-check using the finger method again. Note: if the plant is in sandy soil, you will need about 50% more water than otherwise.
Rhodies may need a little bit more pruning once they are done flowering because the stems sometimes tend to cross. While hydrangea stems all grow from a crown instead, you have to deadhead dried-out hydrangea flowers that are still clinging to stems or prune some hydrangea stems that do not leaf out because of harsh winters.
Both plants should enjoy lots of mulch, about 3-4" inches up to the drip line. With hydrangeas, you can use either regular or acidic mulch but with rhodies, I recommend acidic mulch only.
Rolling and drooping of leaves is very common amongst rhododendrons that suffer from:
* lack of water, too much heat or extreme cold. That is how your plant prevents loosing yet more moisture. By doing this, less of the leaf surface is in contact with the sun and thus, less moisture is lost. To correct this, tale appropriate action. Provide adequate moisture or just wait until temperatures return to normal.
* damage from applications of insecticides (done to nearby plants)
Luis
This message was edited Mar 15, 2009 2:21 AM
