Overwintering purple fountain grass

I love ornamental grasses, and one of my favorites is purple fountain grass (Pennisetum setaceum 'Rubrum'). I think I had six plantings of this last year, and this year I want to have more. The trouble is, this grass is not cold-hardy enough to survive our winters.

Fortunately I've discovered that it's not too hard to overwinter under lights, so each fall I take small divisions, pot them up, and bring them inside.


This year I waited much longer than usual to do this, and although I've been bringing a potted purple fountain grass into the garage whenever cold temps were expected, the plant is looking a little, well, brown.

It's all I have to work with though, so I'm going to forge ahead. It still has some green in it, but that doesn't necessarily mean it's still alive.

Step one is to remove it from the pot, cut the plant back to about 6-8", and assess:

There are some good roots but it's not too rootbound, so this won't be too difficult!

I'll remove as much of the soil as possible from the roots. Since I'm doing this in the garage and don't want to make a big mess, I won't whack it on the ground like I usually would outside. Instead I'll put it into a bucket and quickly and forcefully hit the rootball against all of the sides of the bucket. I'll do this for a minute or so until all of the soil is gone.

Again, I can see what looks like fresh growth, so I think the plant is still alive:

I now use the loppers to cut the rootball in half:

If this were a larger plant I'd cut it into quarters -- the goal is to get a chunk that's easy to work with for the next step, which is to start pulling the clump into smaller clumps:

You might need to cut some roots, but you can wiggle these apart with some effort. The connections between some of these stalks are not too strong, so it seems like there are a bunch of smaller clumps all growing next to each other -- they really were connected into a single plant though.

I want small divisions, just a few stalks each. I've learned that too large a division makes for a rootbound plant by the end of the winter, and even a single rooted stalk will form a good plant over the next few months.

So now I have all of my divisions:

I'm even going to do a more extreme test, and see if this tiny piece that broke off will live and grow:

I like to experiment when I have plenty of plant material like this. It helps me learn how careful (or careless) I can be when I do this again next year.

So now I just need to pot these up. Since they're grasses, it's pretty foolproof. I'm using "quart" sized nursery pots which I've saved from all of my plant purchases over the years, filled half or slightly less with some potting mix, and added some time-released fertilizer.

Plant goes in...

More soil, and done!

You have to pack the soil in pretty well, and although the depth at which it's planted is not too critical, you don't want to test the limits of the plant too much. I've found it's better to plant a little deeper than it seems like you should, then you can pull the plant out a little bit if needed. It's not really possible to force the plant deeper if you didn't plant it deep enough, and you can only add so much extra soil until you've got too much in the pot.

After repeating for each plant, I've got them under my grow lights now:

I like putting my indoor plants into these flat storage containers:

These containers allow me to water the plants without fear of runoff going everywhere, allow me to really deep water the plants if needed (by putting an inch or so of water in the tray) -- really handy if you need to leave the plants unattended for a few days or longer, or to rehydrate very dry soils, and also let me easily move all of the plants at once. If you can find a style that has straight walls and a flat bottom, those are perfect!

I'll know in a couple of days if I was successful with these divisions, as these cut ends will start elongating:

That's where the new grass blades will emerge first. Then new shoots will start forming from the base of the plant, sometimes emerging from the soil:

Once I see those new shoots on each division, I can relax, knowing that I have my purple fountain grass plants for next year.

As the plants grow I will probably give them a "haircut" a couple of times during the winter. I'm not concerned about the top growth too much, but I do want good masses of stalks and roots. I may divide these again in a couple of months if they're doing well so I can get even more plants, as I'm thinking of planting larger masses of these next year, something like this:

(Those were taken in Marina del Rey, California) I think the masses of the dark grasses are really impressive, and I'm hoping I can pull off something that looks this good in my yard next year.

But first things first: mass plantings require masses of plants, and I hope that's what I've got started today.

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Gerhard Bock (Succulents and More)  – (December 4, 2010 at 11:44 AM)  

Like you, I love purple fountain grass, and many other pennisetums. We have three in pots and they overwinter fine in our climate but this year they're completely root-bound. Would you suggest dividing them now (and replanting them outside in pots) or wait until late winter (which is February here)? Since they're not really doing much growing right now, I'm tempted to wait until February.

Alan  – (December 4, 2010 at 7:29 PM)  

If they're really not growing, then I don't think it makes any difference. Since you've got three though, you might want to divide one of them now and see if it makes any difference. That's what I would probably do (I like experimenting).

GrowingHabit –   – (December 5, 2010 at 2:39 PM)  

Hello Alan

Frequent visitor to your blog (as in, its been added to my bookmark menu, and I visit daily) but slow to speak up. Had to finally, because I really wanted to share a website, if you all haven't found it on your own, yet. Its my favorite, for ornamental grasses. Check out the grass-scapes gallery. On dividing: http://www.bluestem.ca/dividing-grasses.htm

Alan  – (December 6, 2010 at 7:09 AM)  

Thanks for the link! Bluestem is a great source for info on grasses it looks like. I wish the gallery images were larger though.

Sue L'Hommedieu –   – (October 31, 2013 at 9:57 AM)  

Alan, I'm reading your posts from the past. How did this work out? . I tried pulling a big pot of Purple Fountain Grass into the garage for the winter , but it didn't make it.I've been buying new plants every spring. Luckily, they are now available that the big box stores for about $5.

Alan  – (October 31, 2013 at 11:09 AM)  

Sue -- this works great! I did several follow-up posts. The key is to keep these small divisions warm with plenty of light and water. Overwintering in a cool, dimly-lit garage didn't work for me.

Unknown  – (May 23, 2016 at 12:38 AM)  

I bought a couple of these, potted, at a nursery. My hope was to divide them, but they are really root bound. Can they still be divided and re-potted do you think? I'm only able to do container gardening where I'm at. Thanks in advance for an advice.

Alan  – (May 23, 2016 at 9:26 AM)  

Nicole: I think they should be fine if you divide them -- grasses are so tough! Just make sure that the roots on the outside are still white and healthy. If they're brown and rotten then remove as much of those as you can.

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