Saturday, March 7, 2009

The great Pennisetum debate

About a week ago Jenn, of Garden Djinn posted a question to me, “As a professional landscaper in the phoenix area, do you plant fountain grass, Pennisetum setaceum, and if you do, can we talk about it? It is considered an invasive plant.”

Here is the culprit above.
Pennisetum setaceum - 'Green' Fountain Grass

A native of South Africa, it seeds numerous times during the year and crowds out or own native species in sand washes and creek beds.

Well I recognized the name and I had planted some Pennisetum setaceum – Purple Fountain grass last year. What the heck? This had me worried. I got on the phone with a couple of the growers I buy from including Mountain States Wholesale Nursery, and this is what I’m told:

Above are three of the plants local growers are selling:
Pennisetum setaceum – 'Purple' Fountain Grass.

Yup. They are both called Pennisetum setaceum. But they are different cultivars. There are actually more then two, in fact Mountain States grows there own version called Pennisetum setaceum – ‘Eaton Canyon’, or ‘Red Dwarf’. The red and the purple don’t seed as prolifically as the green fountain grass and most of the seed produced is sterile. How do they know this? They tried it with a test group of 'Purple' and 'Eaton Canyon' before they ever sold a single plant. I did find out however, that if there are some green Fountain Grasses near by, the purple and the red can cross pollenate and make more green fountain grass.

I do have one more call to make, a guy from the Arizona Native Plant Society. I'm saving him for last. I wanted to hear what the local growers were saying before talking to anyone from AZNPS. If I find out anything new, I’ll post it. I the mean time, git yer hoes and dig up some Green Fountain Grasses. Thanks Jenn for your question.

Here is a closer look at a Pennisetum setaceum - Purple Fountain Grass.


  1. Thanks for the info. I have this grass, need to check the variety.

  2. Hi Tatyana,
    Be careful not to get a Muhlenbergia capillaris confused with the Green fountain grass. The difference is; the seed heads are much more dense on the Pennisetum then the Muhlenbergia.

    Check here:

  3. Purple Fountain Grass is a safe grass to plant here in AZ. We learned the difference in it and the green kind during my classes at DBG. I have several in my garden and never had a sprout from any of them. I love this grass, as it contrasts so nicely with all the yellow in my garden.

  4. Good to get the word out on the fountain grasses. I planted some red ones 10+ years ago and have encountered only one seedling in all these years--way less than self-seeding among all the other plants in my garden. However, our local canyons are full of the escaped green versions. I believe I've read that there are also some sterile green cultivars, but since they look like the fertile ones, the Southern California California Invasive Plant Council has put all "cultivars and varieties of this species" on the "don't plant" list. That sounds like they mean even the red versions. I'll be checking into that myself--I really like my red grasses and would hate the pull them out since there are no native grasses that look at all like them. But if you find out anything, I'll check back too. I think different agencies say somewhat different things since science is always an ongoing discussion.

  5. Thanks for posting the DBG position, Aiyana. I was looking for pictures of the green variety on the DBG site, but it was very easy to find some to photograph.

    With the Flower and Garden Show, sick wife and kids, I haven't called the AZNPS folks yet. I'll let you know what they tell me.

  6. Thanks so much for making this discussion public. I have some photos of the grass that has seeded in the preserve, and unless the green leans into purple, these plants have got at least one purple parent.

    I realize that the nurseries do come out with more cultivars all the time, and perhaps some of them are 'safe' to plant, but this is a grass to consider thoroughly before deciding to purchase. And I personally would advise you against the temptation.

    It *is* beautiful and it *is* hard to pass it by. It's just our luck that some of the worst invasives are the best looking - - check out purple loosestrife in the midwest for another prime example of a plant that got away from cultivation and has become a pest.

  7. Another "invasive" plant, actually a tree, that I would advise no one to plant within 30 feet of concrete patios, sidewalks, driveways and so on is called a sissoo. While Bill's opinion might be different, in my experience this tree is like an octopus on steroids, with hundreds of main roots that spread toward any source of wetness, whether water, bleach and/or chemicals designed to kill trees. The sissoo thrives on deadly chemicals and if one part of a root is dead merely begins growing another "tree" from another part of the root.

    I had never heard of such a tree before and had no idea what kind of damage it could do even as I looked right at it while asking my Realtor about it during a "walk-through" of a home I later bought. Apparently, my Realtor was lucky enough not to have experience with the sissoo either, because we both thought what we were looking at was a weed. In fact, at no more than 3 inches tall in the corner of the home's back yard, I could see why my Realtor said it was nothing to worry about.

    It became something to worry about, however, when three weeks later it was a full-grown, if skinny, tree!

    With sissoos of her own in her back yard, my now former next-door neighbor told me more about the tree, relating that years earlier a root from one of hers began to push up and out the block wall standing between her and the neighbor on the other side. The root of the tree was so invasive and forceful, it broke up the block wall between her back yard and her neighbor's, and she had to pay to have the entire wall replaced, along with the gates, etc., and of course to have the tree "killed" and its stump left behind with nails in it.

    This was the beautiful shade tree in my back yard, the one whose roots had already caused a vertical crack in the back yard concrete patio, whose saplings appeared daily from under the rock of the landscape (apparently attached to, beneath the rocks and/or plastic, long, tentacle-like roots, many very thick around, up to 10 inches), including adjacent to the foundation of the house and from the backyard to the front.

    While people who hadn't a clue insisted I keep pulling the saplings day after day after day, I knew what had to be done. I had to have the tree killed. To pull saplings daily and leave the tree's invasive roots to destroy the house, which had already begun, was insane, I thought. Yet many advised I do this.

    I hired a tree removal company that couldn't even kill it or remove and grind the stump. At the time this was done, I didn't realize that the tree wasn't really dead, so I had more landscaping rock put down in the front and back yards. For a few months, all was well. Then a sapling, followed by another, and another and another. I couldn't believe my eyes. So I started digging, and have been doing so a little every day since March or April, to find more roots and get rid of them for good. I also found that the neighbor located behind me must have a very powerful irrigation system because the water from the other side of the wall not only keeps the bottom portion of my side of the wall wet but also one of the tree roots. I have put the fat end of goof plugs in all the drip line's holes formerly occupied by "spaghetti" lines that seemed just a tad too narrow -- water was leaking out from around exactly where the spaghetti lines were inserted and met the main drip line -- and a friend of mine has cut off the water supply to to the back yard, but still I worry that this tree will consume my existence.

    My mother has sissoos in her back yard and several cracks in her patio and the concrete flooring under the tile, yet she isn't worried about her foundation at all. I don't understand why people recommend the sissoo tree. Nothing can kill it and it seems like the tree will not die.