Expert: Long Island Gardener - 8/31/2011

Question
I have purple fountan grass in urns on either side of my steps. I planted them about two months ago, a little later than ususal. Hoewver, they are not thriving. I see fountain grasses in gardens all over my city that look gorgeous, full and flowing. Mine have  more brownish dry stalks than green or purple. It is August, but still very hot here. They get plenty of water. I even checked the root systems to see if they were root bound. They are not. I moved them to full sun. It didn't seem to help. I realize they are annuals, and won't outlast the fall/winter. What can you suggest that I may have done wrong, or could do to perk them up? Even though they don't have flowers, I think putple fountain grass is one of the pretties plants in the world! Help if you can.

Answer
I'm going to be honest, here: This is going to be tough.  Without knowing (you leave really no clue other than that you are north of the Equator) where you garden, and then without knowing what you growing medium you chose for your plants or even how large the urns you are using are, I can only take educated guesses at what the problem(s) might be.  Failure to thrive is a broad question at best; adding these unknown variables makes this a question I should reject with an explanation.  But I hate doing that.  Let's discuss this plant.

First, yes, you can easily divide this plant.  But in the shape it's in, I would figure out what the problem is first.

Oh, yes, the problem.

Let's start with the obvious, your dubious watering program.  Transplants always struggle when their roots are disturbed.  In the case of a plant from Lowe's, you're looking at a lot of pain and suffering, which translates into root damage.  Although this beautiful grass is tough, drought tolerant and easy to grow, remember, it is only human.

But the words 'plenty of water' always make me nervous.  You probably would have discovered root damage when you checked the plant for pot-boundedness.  Still, if the roots are already damaged from summering at Lowe's on those racks no one waters when it's 102 degrees in the shade, you may not have realized the severity of the damage.  It doesn't matter how much you water if the roots are badly damaged and can't take up water correctly.  Watering daily can do more harm than good.  I understand that in desperation, you may have given this plant too much of a good thing.  Consider that carefully when you try to diagnose what's wrong with your Pennisetum.

Look at it this way.  Just because it looked good when you bought it didn't mean this plant was not ready to kick the bucket.  This is a tough plant.  That means it has nerves of steel.  It doesn't mean its kidneys aren't failing, or its leg isn't broken and gangrene is setting in.  It's just really good at looking beautiful even when it fails to thrive.

So we have here potential WATERING issues and potential ROOT damage and possible PTSD.

Let's continue.

Container growing is not the piece of cake it appears to be.  Sure, many people do it well, people who can barely read or boil an egg can be good at it and you may be looking at those people thinking, I know I can do this.  And you can.  Just don't assume it's a piece of cake.  There are people out there with driver's licenses who should never be let out of the house.  They stay home and do container gardening.  They get lucky.  Good for them.

When plants grow in a closed container, like an urn, they are deprived of one of the most magical experiences in Nature: An alliance with underground Vesicular arbuscular mycorrhizae.

These are the invisible friendly Fungi that seek out compatible plant roots and bond with them.  This friendship can go on for years, growing stronger each season.  Let's get this straight: Something like around 80 percent of all plants are estimated to establish alliances with these amazing microbes.  And to think that few people had ever heard of them 10 years ago.

Cut off from the earth, however, your potted plants pass their days in solitary confinement, often thriving, but never with the vigor of a ground-grown specimen.  It's those VAMs that make your Purple Fountain Grass so adaptable.  They pour nutrients and moisture straight into the roots, until, under the right conditions, life is just a bowl of cherries for everyone involved.

Finally, it is possible that under the care of the brown thumbed Lowe's truck drivers and clerks (well meaning they may be, but look, there's just so much they can do with all those gazillion pots that get delivered by the boatload and always on days where it's 110 degrees in the shade), the potted plants you purchased were so beaten up by weather and neglect in the Lowe's "greenhouse" that not even triage could have saved them.  Are these hanging onto life by a slender thread?  Truthfully, at this point in the season, even that is a miracle.  That does not mean however that you cannot save them.  It just means they failed to thrive because they were, more or less, in a coma, and are improving slowly (and imperceptibly) under your loving care.  And now you ask: What am I doing wrong?

Enough.  What can you do about this plant?  What would I do?

First, re-pot.  Give this plant half sharp sand and half a good dark humus and loam mixture, to discount any possibility that overloads of fertilizer salts are singing the roots as we speak.  Oh - rinse those roots well, in lukewarm water.  And if you really want to do this right, add a few scoops of American Soil (or French Soil if you are in Gaul, Italian Soil if you are in Rome, Russian Soil if you are in Russia, etc.).  Those scoops will hold cultures of helpful microbes that may just save these specimens.

Next, give the plants shade for a week or two.  Then get it out in the open to promote photosynthesis and give it extra energy.  These are naturally full sun plants.  The deep purple pigments you see are the evidence of anthocyanins, and it takes a lot of energy to make them.

Because of this, in fact, when this plant is grown without enough light, they make less purple.  Take a look at the pigment production and get back to me.  We'll read together one of my favorite studies, titled 'Relationship of light quantity and anthocyanin production in Pennisetum setaceum', published in the Journal of Agricultural and Food Chemistry.

Cease watering except to provide a guzzle of the hose when the soil is fairly dry.  Of course you may be doing this just fine, I just have to mention it, because it's the biggest single mistake in the gardening world.

Happy Labor Day, my friend.

THE LONG ISLAND GARDENER