Nevada Public Radio Listen Live

"BBC World Service"
Facebook Twitter Follow Nevada Public Radio

Support Nevada Public Radio
January 10, 2006

DESERT BLOOM: Cooperative Plants


Angela O'Callaghan explains why some plants play nicer than others.

When we're planning a garden for the spring (or any season, for that matter), one of the things we really should consider, but seldom do, is how well plants do with each other. We're pretty familiar with the concept that plants have evolved resistance to certain diseases or insect predation, but this is a little different.

Now, I'm not talking about how you place them in your planting beds. You definitely have to make sure that one's not crowding out another, or shading out another. You know you don't want to put a pumpkin plant, with its huge leaves, next to something that'd be overwhelmed, like basil. No, this is still another thing.

Several years ago, there was a series of gardening books with titles such as 'Roses love garlic' or 'Tomatoes love carrots' (or something to that effect). I didn't read the books, but they certainly point out a scientifically proven fact - some plants produce chemicals that have genuine effects on other plants.

In the case of those books, the effects were positive. The benefits can be the result of lots of different factors - sometimes the roots of one plant will secrete a chemical, which could be a hormone, or a sugar, or heaven only knows what) - that stimulates a neighbor to grow. Some of them can give seeds a push to germinate, and others might promote flowering. That's the background of the practice known as 'companion planting'. But not all of these interactions are positive. In fact, when people first started looking closely at them, they were noticing some very negative events.

The name of this phenomenon, for those of us who must know such things, is 'allelopathy'. Most of the plants that are allelopathic seem to produce something in the soil. I started looking up references on it, and found many more than I'd expected. Apparently it's been one of the hot topics in horticulture for the past few years.

Now, people have been growing plants for, oh, about 10,000 years. Wouldn't you think that somebody, way back when, would have noticed these kinds of interactions? Well the fact is that people did notice them, and describe them. Like the classic Black Walnut- there are many plants that cannot grow well if they're at all close to this tree. The roots secrete a chemical that's toxic to other plants. The ancient Greeks knew about this one. But for a long time, scientists were dubious about the whole concept of allelopathy. It's no wonder, really. It's often not just a case of one root, one chemical, one effect. Nothing's usually as simple as the black walnut.

Everything's more complicated than I'd like. What are some of these interesting plants? Well, they're certainly not all that uncommon. Eucalyptus, which I love, might have some toxicity to certain members of the grass family. Then again, some grasses are toxic to certain trees.

For instance, I found a scientific paper that was published last February. Researchers reported that fresh needles from Aleppo pine can interfere with the growth of Bermuda grass. At last, maybe there's a chance I can get rid of the Bermuda that insists on poking its runners through my rock mulch! But even more bizarre, I found another article from a few years ago, where researchers in Oklahoma found that Bermuda might limit the growth of pecan trees!

There're a couple of common weeds called 'knapweeds' that are major problems in the wild parts of Nevada. These plants not only out-compete our native plants for nutrients and water, but it turns out they produce chemicals that affect native plant root growth! Talk about adding insult to injury. But then again, there's some evidence that this plant might inhibit the growth of its own seedlings, the same way that creosote does. Now, there's a real effort to determine how the compound in knapweed could be used to limit other weeds.

There's lots of research going on. After all, if one plant can keep another one from growing, wouldn't that be a terrific alternative to commercial herbicides? In fact, that's one of the driving forces in the research. Trying to get the plants we want to crowd out, or even kill, the plants we don't. Gotta love it.

Quite a bit of the research is still in the 'Well it seems' category. In a publication I got from Florida Cooperative Extension, there's a statement that lantana can suppress milkweed, and even chaste tree can retard the growth of certain grasses.

Well, I think that's enough complication for now. The point is that some plants produce chemicals that interact with other plants. We usually only notice when they interfere with each other. And sometimes we don't even notice, then.

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

See discussion rules.


AngelaFeb 19, 2015 | Tricky Spring
If you're thinking that our warm weather means your plants are safe from a late frost, you're probably right. But then again, you never know. It only seems that Jack Frost has skipped a visit to Southern Nevada this year. Here's Angela O'Callaghan with Desert Bloom.

NormFeb 14, 2015 | Selective Pruning
Norm Schilling guides gardeners to keep up as Spring approaches. Selective pruning will keep things on track in the yard.

NormJan 21, 2015 | Prepare for Spring Now
Don't look at the calendar. Look at your plants to tell you what do to in the yard right now. Your plants think Spring is near, so use this time to transplant and prune. Desert Gardener Norm Schilling tells us what to look for.

NormDec 30, 2014 | Winter and Citrus
Citrus can thrive in Southern Nevada - even in our cold - when you choose the right varieties. Norm Schilling tells us how.

AngelaDec 13, 2014 | To Prune or Not to Prune
As winter draws near, leaves begin to fall. And the bare view may prompt some excessive pruning. It's tempting, but your plants may appreciate a little restraint. Here's Angela O'Callaghan with Desert Bloom.

NormDec 6, 2014 | Prepare Your Plants for Cold Weather
It's not cold . . . yet, but Norm says be ready and your yard will appreciate it. Don't let a cold snap cost you your investment in plants in your yard. Norm Schilling has some ideas to get ready.

AngelaNov 25, 2014 | Evergreens
As we head into the holiday season, more attention is given to 'evergreens.' Too many cones on a pine tree might be a sign of weakness. Angela O'Callaghan tells us all about evergreens on Desert Bloom.

NormNov 14, 2014 | Fall Colors
Even in the desert, Fall colors can brighten your landscape. Here's Norm Schilling with Desert Bloom.

NormOct 28, 2014 | Fall Colors - Web Only Edition
With glorious weather for our yards to fall back into bloom, Norm has some additional suggestions for color to add to the profusion of blooms for this time of year. (Web-only content)

NormOct 7, 2014 | Second Spring
The call it a "second spring" Norm Schilling has some plan ideas to make Fall colorful in your yard. He has a checklist of plants looking their best, because now is the time to plant in Southern Nevada.

AngelaSep 30, 2014 | Fountain Grass
A weed by any other name is still a weed even if it doesn't look like one. If only everything in our gardens thrived as well as weeds. Here is Angela O'Callaghan.

NormSep 15, 2014 | Desert Heat
Norm describes a significant casualty of the desert heat. There's going to be a big gap in Norm's Yard and a lesson on the reality of our desert landscape.

AngelaAug 12, 2014 | Organic Pesticides
Choosing a method for ridding your garden of an unwanted guest, be it bug or weed, is not always a simple choice. But the more you know, the better it goes. Here's Angela O'Callaghan

NormJul 28, 2014 | Lose that Lawn
We know, it's a desert out there including every place there's a lawn. Norm Schilling reminds us all the ways he wants you to consider losing the lawn... permanently.

AngelaJul 14, 2014 | Protect Fruit Trees from Birds
If you put a good deal of care into growing fruit trees, there are likely some birds who will take advantage of your effort. Here's Angela O'Callaghan.

NormJul 10, 2014 | Palm Care, Part 2
To keep, or not to keep. Norm Schilling ponders his palm trees, on this edition of Desert Bloom.

NormJun 10, 2014 | Palm Care
Norm Schilling has mixed feelings about how we use Palms in our yards. Full grown palm trees transplanted into the entry way of a mall is a common sight that tells Southern Nevadan's "something" is nearly open for business. He reminds us that those palms come with challenges.

AngelaJun 3, 2014 | Hot Weather Plants
As temperatures across the Valley begin to climb, you might be wondering what will survive in your garden in the months ahead and what probably won't. There are some 'sweet' options. Here's Angela O'Callaghan

NormMay 20, 2014 | Desert Color
Norm Schilling just got back from Belize and has some ideas for lush leaves in your desert yard. He reflects on some well suited plants to provide color and variety in this edition of Desert Bloom.

AngelaMay 6, 2014 | Emerald Ash Borer
Raising a healthy shade tree in the Mojave is not always easy. And if one particular insect makes its way here, it could get even harder. Here's Angela O'Callaghan with Desert Bloom.

Web hosting facilities provided by Switch.