With our challenging environment here in the desert, it's surprising to me that weeds would even get established here, but of course they do. When I was teaching a weeds class recently, someone asked me for a good definition.

My personal definition is "a weed's a plant that's growing where you want something else, and it's doing better than the things you did plant".

You could consider any plant to be a weed if it's growing where you don't want it. Or when. For instance, if you had carrots in your garden last year and they came up again where you now want your tomatoes, then those carrots are weeds.

Usually though, weeds are plants that appear and you never want them. Things like Russian thistle, tumbleweed. It's a seriously awful plant, and while there might be some creature somewhere that likes it, most of us find it a horrible, invasive and noxious weed.

I had a class describe how they'd build a perfect invasive weed. It could have many seeds, or reproduce through additional, asexual means. It'd be able to survive a range of environments, spread easily. It'd have minimal requirements. In some ways, that might sound like a plant we'd want to have in our own gardens.

But it brings us to the question, what is it about these plants that allows them to become weeds? There are several ways. A number of weeds got carried in as a contaminant in grain, or on an animal. Nobody ever said that weeds had to be ugly, and some of them started out as lovely ornamentals. For instance, salt cedar was brought into this country from Asia to help stop soil erosion and as a garden shrub. Now, it's a noxious threat that crowds out native plants all over the west, uses large amounts of water and turns our salty soils even saltier.

In general, these invaders have no natural enemies here, and they're quite happy with the environment we provide.

Invasive and noxious are serious problems, and they're different from plain old garden variety landscape weeds. An invasive plant is not only growing where we don't want it, but it can crowd out or inhibit the growth of other plants in the new territory where they've invaded. This is a serious problem in wild areas, where the delicate balance of soil, water, plants and animals gets thoroughly thrown off. A noxious weed is actually a legal concern. It's not a native plant, first of all. It's invasive, so if it were planted, it would spread out far beyond its original site, elbowing out any neighbors to seize water and nutrients. But most critically, a noxious weed causes serious harm possibly to animals, the environment, even the economy. Nevada, and every state, has its own noxious weed list. Some places list Norway maple trees, others lantana. You can easily find it by looking at the Nevada Department of Agriculture website.

Some of these plants can be bigger threats than others, depending on where they're growing and what's around them. I couldn't even say what the biggest problem is. I'd guess that it'd be the plant we haven't learned to address yet. My personal fear is that it's some lovely plant that we'd never expect to escape cultivation, but will, and it would be.

So what's being done? Here in the south we have the Nevada Naturalist program, where people are trained to work as volunteers with natural resource specialists at a number of locations around the valley. Northern Nevada has the Weed Warriors who deal with problems that are specific to that area.

This doesn't mean that you have to wait until a specialist comes around to take care of weeds. Start with your own garden. After all, we all know what some things are. It's easy to spot a Russian thistle or a salt cedar seedling and pull it up. Cooperative Extension's website has lots of fact sheets that're guides. Take a look!

For KNPR's Desert Bloom, this is Dr. Angela O'Callaghan of the University of Nevada Cooperative Extension.