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Rhododendron ABC's #7

At this stage in our rhododendron discourses, it may be time to change the title of the discussions to MNO's or perhaps even RST's, since we have learned quite a bit about our favorite genus of plants and are past the halfway point in what a person newly inoculated with Rhododendronitis should know in order to survive and prosper with the "ailment".

We come now to the situation where the basic item of selection of rhododendron plants with the proper hardiness for one's region has been made. What to do then? Of utmost importance for the future well-being of the plants, with accompanying satisfaction for caretaker, are planting site, selection, and preparation.

In this short discussion, it is not possible to list all the items that need to be considered, but there are certain very important things that must be understood. In this section of ABCs (or is it RST's), we will outline site selection and list several things that the novice enthusiast should take into account before actual planting. And next, we will discuss the actual planting.

As I have previously mentioned, rhododendrons are usually found in the wild in cool, well-watered regions that, as a result of rain water leaching, are on the acidic side of the pH scale (pH is mathematical function or number running from 0, very acidic, to 14, very alkaline, with 7 being neutral). It has been found that rhododendrons are most happy with pH's of from 5 to 6.5. So the first step is to ensure that the planting site is not alkaline. The correction of alkaline conditions can be accomplished in several ways.

Judicious use of elemental sulfur or ferrous sulfate is effective. The ferrous sulfate will also help green up the leaves of plants. Frequent checks of the pH should be made, either with the pH meter or more rapidly with pH papers. Organic matters such as peat moss or oak leaves can also be used. These help to control pH and are beneficial in other ways to the soil of the planting site.

If one is considering plantings near the foundations of newly constructed homes, be very alert for the presence in the soil of lime and cement. As favorite disposal practice for builders is to bury any excesses of these common building materials near the foundation walls of new buildings. A rhododendron encountering these buried materials will rapidly decline in vigor and will likely expire unless radical steps are taken to correct the alkaline environment.

There are a number of other things to consider while choosing sites for one's plants. One often hears that rhododendrons are shade-loving and many times they are planted in dark, wooded areas. This is simply a "bum" steer. It is true that many of the plants do not like to be exposed to full sunlight (especially from, say. Noon to four PM), it is also true that they require light to do well. Plants grown in deep shade are slow to flower, are susceptible to insects and disease, tend to be leggy and have a loose, scraggly appearance. A good correlation can be made between the size of leaves and tolerance of exposure to sunlight. The larger the leaves, the less sun tolerance and conversely, the smaller the leaves, the more sun tolerance. Indeed, any of the small-leaved, dwarf alpine varieties, thrive very well in full sun and will not do well at all in shaded areas.

In any case, the plants should have at least indirect light overhead. North and East sides of buildings are good (again, open overhead). Open glades in woods are also satisfactory but, remember, the plants should be able to see some open sky over their heads for a good part of the day. If the planting site is wooded, make sure that low branches of trees are removed so that the canopy is raised. Our favorite plants need light!

The matter of eventual size should be carefully considered. Many times the old humorist's adage, "kittens grow up to be cats" is ignored. Likewise, cute little rhody plants can expand to take up a lot of space. It is best to consider the estimated ten year size of the plants and make proper allowances -- don't put a potential ten-feet high shrub in front of your favorite picture window!

Try to choose a location that is sheltered from severe wind exposure. Especially in winter, leaves can be stripped from exposed plants by the force of winds. Also, severe winds can damage plants by excessive water evaporation from plants with broad, evergreen leaves. Also, in winter, even very hardy evergreen rhododendrons may suffer severe damage if leaves that are frozen on cold nights are exposed to bright sunshine the next day. Try to plant where they will not be quickly thawed by bright sunshine.

Lastly, take into consideration the types and shrubs that will be close neighbors of your rhododendrons. Some shallow rooted trees can be fierce competitors for water and nutrients. It is, for example, very difficult to keep rhododendrons in good condition if they are planted close to Western Red Cedars (Thuja plicata). You must choose companions for your rhododendrons, carefully!

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Dave Goheen