I have experienced and read, that some varieties of Pennisetum alopecuroides, in particular one called 'Moudry', can be vicious self-sowers, particularly in warmer climates.

As for Miscanthus, I have never experienced them self-sowing, although it also may be possible in warmer regions.

Make sure you get a clumping Miscanthus sinensis cultivar, not an invasive one that spreads by runners. M 'Adagio' or 'Little Kitten' should not spread by runners. I have grown Miscanthus sinensis 'Morning Light' for 10 years, and it has not run or set seed. The clumps just get larger, and then tend to die out in the center of the clump.

john, I'm curious, which Miscanthus spreads by runners?

The only one that I've ever had a problem with in terms of the clump getting too big after several years, is M. giganteus.

I should have mentioned it's Pennisetum (fountain grass).

Miscanthus sacchariflorus spreads by invasive rhizomes. The ornamental cultivars of Miscanthus sinensis are not the same as the wild type of M. sinensis or M. sacchariflorus. They may also by spread by reseeding, however.

check out: http://www.horticulture.umn.edu/miscanthus/ornamental%20uses.html

Here is a link that might be useful: Miscanthus sacchariflorus info

It's because of the zone. I've had this discussion with people from a local nursery. Around here, pennisetum isn't a problem since they set seed so late, and the seedlings have hardiness issues. However, further south, they are officially invasive. So that particular nursery doesn't want to sell them since a lot of their clientele are weekenders who are very likely to be bringing plants south.

I've heard panicums were terribly invasive by seeds, so have always avoided them. Is that not true?

I have Panicum 'Heavy metal' and I have never had any problems here in Zone 5.

A local expert said that Panicums do not reseed here in zone 7.

Oat Grass has reseeded for me -- I have one extra clump after 2-3 years, so it has not been terrible -- yet!

Hubby and I created a grasses garden as part of our side boundary out of various kinds, including miscanthus. I discovered I'm very allergic to a substance in the leaves, especially on a hot day when I'm sweating. Terrible rash that lasted a long time. When we wanted to reduce the clump of miscanthus giganteus (it truly is enormous), my husband had to use a chain saw to cut through the root system. However, it doesn't seed itself around.

Miscanthus 'Little Zebra' and 'Cosmopolitan' are very well-behaved in zone 7. They have never appeared anywhere else, the clumps just get larger until they need dividing.

I am in the process of pulling all of the Love Grass (eragrostis) from my garden as it is a TERRIBLE seeder -- the seedlings show up in the gravel driveway, between pavers and in my garden soil.

Cameron

My panicum Prairie Sky hasn't seeded in four years--clumps just get larger, need dividing, that's it. This is my first year planting miscanthus (Adagio, Morning Light, Variegated, Little Zebra--I sorta went nuts this spring) and pennisetum (Hameln, the purple annual Rubrum, and an unidentified variety)--will keep an eye out for problems, but I don't think I'll have any in my zone.

Some grasses will reseed (sometimes prolifically) if they are sited next to a gravel drive or a porous patio, but otherwise don't. The great drainage must be the perfect medium for seed starting these grasses (Eragrostis, Muhlenbergia capillaris, some Panicums, blue fescues). I've never had a single seedling from any of the Miscanthus, Pennisetum 'Karley Rose', and most Panicums. My favorite smaller grasses are: Miscanthus 'Little Zebra', Muhlenbergia capillaris, Stipa gigantea (a see-through plant), and Panicum 'Heavy Metal'.

Muhlenbergia capillaris looks really intersting!

invasives can spread without your noticing. The seed is carried away by wind or birds and appears elsewhere. A lot of miscanthus is invasive. Miscanthus sinensis is illegal to plant in NY.

Miscanthus does not spread by runners. But it can self-seed in specific locations with the right conditions. btw, Miscanthus sinensis is regulated but not prohibited to buy or plant in NY.

it seems a temperature thing

they need a warm long season to start flowering at all, and more warmth to have ripe seeds

in Germany and Switzerland Miscanthus starts to get problematic, or rather

the first findings of seedlings occur. the recommendation ist to use only cultivars (as seedlings are more prolific) and if you fear that yours could develop seeds, the suggestion is to "Chelsea-chop" them: take about a third of around May/June which will just delay them enough that it is too little time for rie seeds.

the location of your garden within the landscape is an important factor, if you are close to the country side, you should be extra carefull.

and if they produce runners, it`s a different species/ wrong labeled stuff.