The Coastal Gardener:

April 23, I was looking at the displays at the big garden show at South Coast Plaza. As I rounded the corner I saw a booth with a nice collection of shrubs, perennials, vines and grasses.

I stepped closer. At the front of the display I quickly noticed a large table of plants, separated from the rest of the display. On the table was a prominent sign that read, “California Natives.” Terrific; I was pleased to see many familiar native plants on the table. These native plants were clearly popular, attracting a lot of attention.

However, at the very front row of the table I was shocked to see two very “un-native” ornamental grasses. Surely, this was a mistake.

One was a familiar grass known to most gardeners simply as green fountain grass (Pennisetum setaceum). The other was Mexican feather grass (Nasella tenuissima or sometimes Stipa tenuissima).

In the friendliest voice I could muster, I anonymously mentioned to the two proprietors, “Nice plants, but these two grasses are actually not native plants.” Giving them every benefit of the doubt, I figured that maybe this was just a mistake. Maybe they didn’t know that these two plants were not native.

I went on to point out, “Fountain grass is from Africa and Southeast Asia, and feather grass is primarily from South America through Mexico.”

They clearly didn’t want my assistance, nor did they appreciate my correction.

Hmmm.

Still, staying in my good-neighbor mode, I explained that these two ornamental grasses were in fact enemies of native California plants.

To that comment, the owner had just about enough. The response was clear and firm, “We get a lot of requests for those and they sell really well.”

“Yes, but ... ” I gave up.

Green fountain grass first became popular in local gardens 20 years ago. Gardeners found that it was trouble-free and easy to grow. Tens of thousands were planted in the ensuing years.

Unfortunately, green fountain grass liked California too much and began seeding where it didn’t belong. Today, green fountain grass (not the red-leafed forms) is a serious invasive plant, seeding into our wild areas.

Out-of-control armies of green fountain grass have been pushing native plants aside in a relentless expansion into our natural areas.

A drive through Newport Back Bay, a walk along the bluffs of Crystal Cove or a drive up the Ortega Highway will attest to this plant’s aggressiveness and damage.

Five or 10 years ago, Mexican feather grass became the new darling of the ornamental grasses. Its soft, fine-textured leaves and supple flower heads bend and blow in the slightest breeze, a somewhat romantic site. Like green fountain grass, its drought tolerance is superb. But, it too seems to like California just a bit too much. These same breezes also disperse tiny airborne seeds to places they don’t belong. It appears that Mexican feather grass may also be establishing itself in our native areas.

Gardeners should avoid these two ornamental grasses when buying plants for their gardens. If they’re already in your garden, you’re forgiven; you probably didn’t know. However attractive they may be, these are ecological thugs. It’s not worth the consequences. I urge you to replace them with plants that are less threatening to our environment.

And if you see green fountain grass or Mexican feather grass for sale in local garden centers you might also pass along your concerns to the proprietors. But please use a friendly voice.

Ask Ron

Question: Do hydrangeas need an acid fertilizer? I keep hearing different stories on this and now I’m confused.

Tina

Newport Coast

Answer: This myth won’t seem to go away. Hydrangeas will do just fine with an all-purpose fertilizer; it does not need to be acidic. Organic fertilizers labeled for roses are often a good choice. With that said, because our Orange County soils are naturally somewhat alkaline it’s a good idea to periodically alternate your fertilizing regimen by using an acid-based fertilizer, such as cottonseed meal. If you fertilize regularly, every fourth or fifth application might be with an acid based fertilizer. This will lower the pH of your soil slightly, rendering it a bit less alkaline. But my suggestion isn’t unique to hydrangea culture, it’s is a good idea in most Southern California gardens.

ASK RON your toughest gardening questions, and the expert nursery staff at Roger’s Gardens will come up with an answer. Please include your name, phone number and city, and limit queries to 30 words or fewer. E-mail stumpthegardener@rogersgardens.com, or write to Plant Talk at Roger’s Gardens, 2301 San Joaquin Hills Road, Corona del Mar, CA 92625.

RON VANDERHOFF is the Nursery Manager at Roger’s Gardens, Corona del Mar.