Vinca

[descodave]

I planted quite a few bright pink vincas in holes in my pahoehoe lava; they did well for quite a while, but now a lot of them have yellowed leaves. Anyone have any ideas what the problem might be & the solution? Thanks!

[kaialoha]

First thought is that you haven't cut them back. Are the leaves closer to the roots turning yellow while the tip growth is staying green? That would indicate 'leginess' and thinning growth which is what Vinca will do if not cut way back. If you thin them and cut them back the new growth will be more robust and will fill in fairly quickly.

Reasons to Prune: Since creeping vinca grows so rapidly, it can quickly grow beyond the areas where you want it to remain. Watch the progress of creeping vinca and trim it back when it threatens to spill over the confines you've chosen for it. Pruning minor periwinkle also helps to thicken it and prevent it from becoming sparse or thin in spots. Thinning creeping vinca increases the vigor of the ground cover, encouraging it to grow back robustly. Excessive mounding and uneven growth are other reasons to prune creeping vinca from time to time. Plants that have been planted too closely together also require more frequent cutting back.

When to Prune: Prune creeping vinca in the winter or very early spring for the best results. Avoid pruning vinca minor during May and June while it's in bloom to keep from losing the colorful blossoms before they die a natural death. Perform a hard prune every two to three years to control growth, rejuvenate vinca minor and encourage its best performance. A straggly appearance indicates that it's time to prune vinca minor and restore it to a bushy state.

How to Prune: Wipe down a pair of pruning shears with a soft cloth moistened with rubbing alcohol to destroy any remnants that can spread disease from one plant to another. Use a light touch on the sharp edge of the blade to avoid dulling it. Remove dead, damaged and dying branches from the plant first. Always cut back to the node just before the damaged area. To perform a hard prune on vinca minor, cut all growth back to 4 to 6 inches from the ground by hand or use a lawnmower with a newly sharpened blade set on the highest setting.

After the Prune: Water vinca minor after cutting to restore lost moisture. Dispose of the cuttings in a garbage bag tied securely shut. Stray vinca minor stems left on the lawn or in beds may take root and begin growing. To create additional plants, place nodes of non-flowering stems in potting soil. Mist the cuttings well with water and place them in a sunny location to allow them to take root. Plant the new plants outdoors in the spring.

Another problem may be the pH of the soil in which you are growing them. Most soils in Hawai'i ne'i tend to be acidic, so your issue MAY BE TOO MUCH acidity and can be treated with agricultural gypsum. I VERY HIGHLY recommend a pH testing kit, which is fairly inexpensive, so that you can monitor your soils conditions for all your plants. If they are too alkaline, you can lower your soil's pH making them more acidic, by using any number of products, ie, sphagnum peat, elemental sulfur, aluminum sulfate, iron sulfate, acidifying nitrogen, and organic mulches, applying them as instructed on the package. The soil pH change will NOT happen quickly but once the balance is achieved, you'll see a remarkable difference in the health and vigor of your plants.

So, the symptom of the 'yellowing leaves' issues can be described and addressed/treated as follows:

1. Soil pH too LOW (TOO MUCH acidity): RAISE pH to between 5.4 and 5.8
2. Soil pH too HIGH (TOO MUCH alkalinity): LOWER pH to between 5.4 and 5.8
3. Legginess due to lack of annual pruning: Cut canes way back and allow to fill in as mentioned above.

In short:

HIGHER pH means MORE alkaline, ABOVE 7.0.
LOWER pH means MORE acidic, BELOW 7.0
NEUTRAL pH is 7.0

But to confuse the matter a pH of 7.9 is 'acidic' compared to a pH of 8.0 or above and a pH of 6.0 is alkaline compared to a pH of 5.9 and lower.
Generally though ABOVE 7.0 is ALKALINE and BELOW 7.0 is ACIDIC

Hope this helps

Punanny

[descodave]

Thanks, Kaialoha - very informative post! I think it could be soil condition or moisture content. Thanks, again!

[kaialoha]

A'ole pilikia a he mea iki ~ ~ ~

Punanny