Saturday, July 30, 2011

What Does Grow Under Pine Trees? By Nancy Szilagyi

Everyone has seen those bare spots under pine trees.  Do you wonder why?  Perhaps you have heard that nothing likes to grow in such acidic soil.  The needles are thick under these trees. They must just make the soil too acidic for anything to want to live there. That’s what I thought.

Recently, I took an on-line class given by Dr. Tony Koski, professor at CSU and Extension Turfgrass Specialist.  I learned that our soil here in Colorado is very high pH--free lime.  Although pine needles fall in abundance, there could never be enough pine needles to lower the pH. Fallen needles may SLOWLY make the soil more acidic, but more likely for the better since it neutralizes the lime. It takes decades to change pH and will not decrease by more than .5 units. There goes that myth!

Following are the some of the real reasons many things, especially turf, don’t want to grow under these trees:

The turf tends to be smothered by a thick mat of pine needles.

Dense, year round growth leaves little light.  The only thing that will get through is ‘left over light’, according to Dr. Koski.  This light lacks     intensity and quality. This ‘left over light’ is what the tree does not use     for photosynthesis.

Any other plant will struggle with below ground competition—tree roots     competing for water and nutrients.  Our tree roots here in     Colorado tend to be fairly shallow.

Evergreens, with their dense growth, shed rain to the outside of the tree     line, so it’s dry under the tree. Without adequate water and nutrients,     most plants will suffer in this setting.

But, what does grow under pine trees?

 I have found a few things that for whatever reason, seem to work well under them.  The first is Brunnera macrophylla.  It has a couple of common names; False-forget-me-not, Siberian Bugloss and Heartleaf Brunnera. This one, my favorite, is ‘Jack Frost’.  It doesn’t mind the dense shade.  It doesn’t seem to mind the thick layer of pine needles around it, and the lacy blue flowers are dainty and beautiful.  After flowering is over, the stems can be cut back all of the way and you are left with the lovely heart shaped leaves for the rest of the season.

  The second, which I have come to count on, is Ceratostigma plumbaginoides, common name, Blue Leadwort. It, too, has dainty, pretty blue flowers, but it blooms later in the season than Brunnera. The flowers are followed by seed pods that look like little red tufts and are quite attractive.  The foliage is semi-evergreen and turns red in the fall. This plant is able to tolerate full sun to full shade!

  The third is Kinnikinnick.  This is a native plant in Colorado.  You’ll find it in the mountains growing quite happily along with all of the evergreens around it.  Kinnikinnick is more of a ground cover with evergreen, glossy, rounded, small leaves.  It blooms with tiny white and pink bells and shows off with pretty red berries in the fall.

All three of these plants will need additional irrigation, however, since lawn sprinklers and rain can’t reach them well, but it’s worth the extra time.

So, at least we know there are choices.  The easiest one would be to allow a natural mulch of needles to occupy that space, and that is just fine.  In fact, I find pine needle mulch quite attractive!  The other choice is to try one or more of the above plants, especially if you must have flowers in as many places as possible!