Can plants encourage each other?

[NYCorchidman]

As Dante points out, certain plants communicate and one good example is the emission of warning chemicals in the air that other plants of the same species pick up and ready themselves for the coming danger.

I was watching this documentary about a particular species of acasia tree in Africa. Many herbivores that feed on this acasia were found dead over relatively short period of time. Scientist went out to investigate the cause of this sudden mass death of the animals.
They looked and looked, but could not figure out what. Eventually, and very surprisingly, they found out that the cause was the asacia itself.
What happened was that there had been a drought in the region and animals in the number that was more than usual were feeding on the acasia. Acaisa is used to being eaten to some degree, but when it was being eaten too much, it started to produce toxins to kill off whatever was eating it too much. The trees then produced warning chemicals that was released in the air and travelled to other acasia trees. When animals came to eat the leaves of other acasia trees, the trees were already loaded with toxins.
All the animals that had bites died.
Amazing, isn't it?

Another example, also something I watched on TV, scientists studied one forest that is mainly populated by hundreds (or thousands even) coniferous trees. Some are very very old and some are very young. The root systems are quite extensive and many of the trees have their roots intertwined with one anothers.
They found that younger trees get the benefit of shared nutrients and other phytochemicals necessary for proper growths. So certain coniferous trees (at least the one that was studied in this program) enjoy living in one big family.

There are many other plants that are territorial, though. Their roots release toxins that will kill off others that are nearby, thus ensure water and nutrients all to themselves.

So, one cannot say plants in general benefit from being grouped. I'm not sure about orchids, but some will benefit and some may not.

Grouping may help with humidity but not too much. It will have to be quite a few plants to have any benefit regarding raised humidity.
Two, in case of pest infestation, grouping plants too close together can be bad.

[Leafmite]

I have the Yarrow growing wild in my lawn, now. Just moved a bit to the herb/flower garden to give it a chance to bloom. We'll see if the plants around it are happier.

---------- Post added at 11:32 PM ---------- Previous post was at 11:29 PM ----------

It depends on what you are grouping. Wormwood is a nice one to group with your other plants. The insects really avoid it....

[Fairorchids]

Grouping plants helps. The more pots (with moist potting medium) you have, the better the overall humidity.

I saw the study about seedlings inhibiting/encouraging each other depending upon shared parents or not. I think it was in either Smithsonian, or Discovery, probably 6+ months ago.

[Dante1709]

I've also heard of companion planting ; usually it's done with herbs, fragrant flowers or vegetables. Certain plants are said to attract beneficial predators or repel pests that attack the other plant. I doubt this is true for orchids, but it's possible.

Multiple plants can ensure that a lot of a water is absorbed through the roots, and that it drains better than just a single plant. Maybe this is beneficial for the plants that like quick draining media?

[silken]

I have also heard that seedlings do better in a compot. Whether that is just because the pot is larger and holds moisture better or what but I have read that more than once.

[NYCorchidman]

Originally Posted by silken

I have also heard that seedlings do better in a compot. Whether that is just because the pot is larger and holds moisture better or what but I have read that more than once.

I've read about it too as I was (and still am) interested in getting flasks.
There seem to be two main ways to go.
Separate them or keep them together.

I believe the benefit of keeping them together might come from no root disturbance.

---------- Post added at 11:45 AM ---------- Previous post was at 11:39 AM ----------

Originally Posted by Dante1709

I've also heard of companion planting ; usually it's done with herbs, fragrant flowers or vegetables. Certain plants are said to attract beneficial predators or repel pests that attack the other plant. I doubt this is true for orchids, but it's possible.

Multiple plants can ensure that a lot of a water is absorbed through the roots, and that it drains better than just a single plant. Maybe this is beneficial for the plants that like quick draining media?

I also have heard about it. However, companion planting usually means planting (or arranging) plants in ways that make the garden presentation the most beautiful and efficient using color scheme, different height, different growing habits and seasons...

Regarding the use of certain plants that help repel pest, I think it is rather overly "advertised" as I find it only minimally effective if at all.

For example, marigold, not the recent hybrid with large flowers, but the more "conventional" types, is known to repel certain bugs due to the chemical compounds these plants release. Hence, they were heavily and widely spread as "pest repellent". Well, the truth is far from this.
To get any said benefit from having marigold around, other plants will have to be literally right next to marigold touching them!

Try a row of marigold and plant some veggies or flowers in between. and do not spray. You will see pests.
That is how effective it is.

[Leafmite]

With Pleiones, they recommend putting the small bulbs in with the large bulbs to prevent rotting as the little bulbs cannot use water fast enough and will rot otherwise. I think that that is also the theory behind a compot. There isn't much root or need of water for those little seedlings yet they need to stay moist...putting more together helps to dry things out faster.

---------- Post added at 11:56 AM ---------- Previous post was at 11:49 AM ----------

I have tried various plants to repel insects and the only one that I have found that works is one type of wormwood that I grow...and...it really works. They have done studies to see why this is so and it contains a few types of compounds frequently used in pesticides. (Hint: Don't drink the real absinth.)