No. They are not.
There are chemicals in them that discourage other plants.

Jeri

Ingrid........

This is only a guess on my part, but pepper trees are allelopathic. I don't know if the tree releases its toxins only through the root system or through all parts of the plant.

I know that pine needles from some pines are allelopthatic and if used as mulch could harm your plants.

A quick look at Google led me to this site.

Smiles,
Lyn

Here is a link that might be useful: Allelopathic plants: nature�s weedkillers

Which species of pepper tree, Ingrid, Schinus terebinthifolius or S. molle? S. terebinthifolius seems like it might be the more allelopathic species, according to a quick Google search. My personal experience is that my largest Mme. Alfred Carriere, Celine Forestier, an known 12'+ everblooming pink china climber, Francesca, and a Vitex agnus-castus are all growing under or into the canopy of a heritage S. molle in the corner of my yard and all are doing beautifully (the only problem being having to give a little extra water because the pepper tree hogs it).

In previous message, that should be "UNKNOWN 12'+ everblooming pink china climber" -- if only I knew who it is -- 8 years of pondering that, so far!

There are both types of pepper trees on this hill. For what it's worth, not even the prickly cucumber will grow under or even near the drip zone of either. They're well established, mature trees and there is a sizable layer of their litter under them. The usual weeds germinate after the rains, but NOTHING germinates in their litter, nor even where there was litter which has been removed after one of the California peppers was removed. I would say, based upon how they appear to have poisoned the soil around and under them, I wouldn't use it. Kim

Thank you all. The trees we have don't have any vegetation growing under them so I'll take that as a sign that this would not be a beneficial mulch.

Ingrid

These trees grow fast and well here on winter rain alone, implying particularly efficient root systems that suck the soil bone dry. No water + allelopathy = no weeds

It would be nice if we could harness this quality in some way to kill weeds wherever we don't want them without having to resort to toxic chemicals. I wonder if anyone has ever done research along those lines.

There are already pre emergence herbicides made from both corn and broccoli. I understand if you're sensitive to either vegetable, the herbicides made from them can trigger your sensitivities. Kim

Kim.

What would the broccoli work against?

Ingrid.........

A friend and I are actually testing some information I found out about our local pine trees, which we call "digger pines". The research said that only the pine needles were alleopathic. My friend knew where we could get some bags of pulverized pine needles ... an entry to a park where cars have driven over them and crushed them ... and we gathered several bags. Supposedly, the alleopathic toxins in the pine needles inhibit the uptake of nitrogen in other plants.

She cut back some poison oak on her property and dumped several bags of pine needle dust on them.

I cut back all of the plants behind my propane tank, including blackberries, and dumped several bags on top of the stubs. We'll see if it works.

But, my research also showed me that there are other issues to consider when mulching other than alleopathic properties. Even using the right mulch can cause problems. If the mulch layer is too thick, the bottom layer of the mulch can "sour", which is not good for the soil. Also, if it is too thick, it can block oxygen needed in the soil to break down the mulch and other nutrients which can impact the vigor of the plants we are mulching.

In nature, mulch is applied a little at time, so it makes sense not to use a very heavy layer of mulch. I don't think this rule of thumb applies during a drought period. As your pepper trees have shown, they drop more leaves during periods of high heat which naturally creates a denser layer of mulch.

Smiles,
Lyn

Kippy, they're pre emergents so they block seeds from germinating. Most of that type do it by creating a layer on the surface of the soil which permits air and water through, but keeps seeds from penetrating. One of their major drawbacks are if you disturb the soil in any way after application (and before they finally break down) it exposes untreated soil and anything there and ready, germinates. So, you do everything necessary before applying it so you don't have to walk on the area. If you walk on it, you get weeds where your foot steps broke the barrier. I found the information some years ago while researching herbicides before purchasing them for work. I wanted to make sure the things I sold were things I wouldn't mind putting in my own environment. And, I wanted to know as much as possible about them to be able to possibly steer customers to more organic mulches instead. I don't remember the specific brand names of the broccoli one. Kim

Kim,

I tried googling Broccoli as a herbicide and have not found much info. Do they make a tea with the leaves/stems etc? Wonder if kale works similarly?

Reason for my curiosity, in our winter veggie garden, I want to plant the four corners and center of the long side with a couple of different Austin red's (Munstead Wood and one other TBD-sons fiances pick for their wedding colors) But, this is a winter veggie garden, so the companion plants will be cabbage, kale, broccoli, chard, beets, peas and garlic. They are all in slightly raised beds that I am working on. And we are pulling or harvesting the last of this winters crops. Curious how the broccoli might effect the balance of the plantings.

Kippy....

I have been reading more from the the link that I posted in response to Ingrid's initial post. There is a message board with the link and some of the posts are very, very interesting about the alleopathic properties of various plants, including vegetables. Neat stuff.

I haven't studied the whole site, but it is on my to-do list when I have a working brain again. (I just came in from outside from several hours of work.)

Smiles,
Lyn

I don't think the roots of the veggies in the raised beds will have a lot of effect on the roses, Kippy. Chemicals derived from plants are usually highly concentrated solutions of particular components they contain. Like worrying about corn causing problems because it contains oil. How many tons does it take to provide enough of whatever to cause the issue? I don't think a normal garden yield would prove any issue. I'd be more worried about the potential of some day having something I wouldn't want to eat possibly used on the roses. As long as you're doing everything, that's probably not an issue, but who knows what someone "helping you" might do? I've encountered one too many stories of the strawberries used under the roses as groundcover with the gardener using systemics for aphids. I'm probably more neurotic about such things than many. I am more comfortable keeping the roses and any food as far apart as possible. What others choose to do is their business. Kim

What would the broccoli work against?

Scalia tried it with Roberts. Didn't work.