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Rhody cultivars that are more adaptable to slightly alkaline soil

Posted by whaas 5a SE WI (My Page) on
Mon, Jun 17, 13 at 22:39

Probably a long shot but curious if there are any cultivars that may perform better in alkaline soils than others.

Suggestions sure would be appreciated!

I have an area that is somewhat protected, shaded, very well drained sand.

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RE: Rhody cultivars that are more adaptable to slightly alkaline

A great deal depends on how alkaline the soil is. If it's significantly above 6.0, raised beds with acid soil would probably be necessary. 'Cunningham's White' is one cultivar that reportedly does quite well in soil in the 6.5 to 7.5 range. For this reason, it's widely used for grafting understock in Europe.

It might also be worth trying some of the tough, ultra hardy and very adaptable varieties such as PJM, the U of Minnesota azaleas, David Leach hybrids, etc. Sandy soil, as long as it has some water holding capacity - this is one time the addition of peat to the soil may be advisable - works well for many rhododendrons.

RE: Rhody cultivars that are more adaptable to slightly alkaline

  • Posted by whaas 5a SE WI (My Page) on
    Tue, Jun 18, 13 at 22:44

'Cunningham's White' is the only cutlivar I have right now, lol.

The new growth looks good but it might be getting too much afternoon sun while it continues to get established.

The UW soil lab told me 6.5 to 7.5 is technically the neutral zone. Anything above 7.5 and the plant must be alkaline adaptable. I'm at 7.4.

A neighbor down the road has a PJM and the foilage color looks good but its quite thin even with several hours of morning sun. Problem with this plant is that I don't really like the color for some reason.

I read up on some of the Leach selections, so thanks for the recommendation.

RE: Rhody cultivars that are more adaptable to slightly alkaline

  • Posted by ericwi Dane County WI (My Page) on
    Mon, Jun 24, 13 at 17:07

Agricultural sulfur works for growing blueberries, here in Madison, WI. I'm sure it would work with rhodies, as well. You can find it at farmers co-ops where they sell fertilizer and seed. A typical amendment for Wisconsin soil would be one cup, scattered around the shrub, on the surface, but under the mulch. No additional sulfur should be added, until a soil pH test is done.

RE: Rhody cultivars that are more adaptable to slightly alkaline

In Germany, they graft many varieties on alkali tolerant root stocks which are usually 'Cunningham's White' or a relatively new series of root stocks called 'Inkahro'. They are typically good down to a pH of 7.5. A friend of mine in the Philadelphia is doing grafting of hard to root varieties for the Philadelphia Chapter of the ARS, but I am not aware of any grafted rhododendrons in the trade.

Here are some 'high' pH tolerant rhododendron varieties:

Rcv. 'Cunningham's White',
Rcv. 'Dora Amateis',
Rcv. 'Myrtifolium',
Rcv. 'PJM' and other PJM type rhododendrons.

Here are some alkali tolerant deciduous azaleas:

R. atlanticum,
R. arborescens,
R. prinophyllum,
R. periclymenoides,
R. viscosum 'Watergirl'
Rcv. 'Irene Koster
Rcv. ‘Lemon Drop',
Rcv. 'Rosata',

You can also use a raised bed and acidify the soil in the raised bed. Beware, if you have alkaline soil, you may also have alkaline water. Rain water is nearly always acidic and an excellent option for rhododendrons.

Here is a link that might be useful: Raised Beds

RE: Rhody cultivars that are more adaptable to slightly alkaline

If you don't care for the flower color of PJM, there are other plants from the same breeder that have slightly different shades of red and pink with less purple. Ones I have seen in person are Olga Mezitt, sometimes sold as just Olga, which is more pink and has more olive foliage, and Landmark, which flowers a deep reddish pink and has red tints to the foliage. Aglo is supposed to be more pink as well, though I haven't seen that one in person.

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