How do druids keep other druids from using Transport via Plants to show up uninvited?

Question

What options do druids have to keep other druids out of their sacred groves?

Some contrasting examples:

• Wizards like to Teleport. To keep out other wizards, a wizard can use Dimensional Lock (on an admittedly tiny area).
• Clerics don't have a lot of teleportation spells. To keep out those clerics with access to the Travel domain, other clerics could cast Dimensional Lock or Forbiddance.

Druids probably have a tree or eighty nearby. If a druid wants to go somewhere using Transport via Plants, I imagine having any "normal plant (equal to the druid's size or larger)" around would be both convenient and thematic.

What problem am I trying to solve? Two problems:

1. As best as I can tell, Druids do not have an equivalent spell on their list the way Wizards and Clerics have Dimensional Lock and the like. Perhaps I've missed a Druid spell from a supplement that fits the bill. If the spell exists and I've missed it, I hope to learn of it.(1) This is the main point of my question.
2. Assuming that there is no "Lock Tree from Transport" type spell, I'm trying to find RAW ways to prevent druids of opposing clans from getting into each others' personal groves. My campaign posits different druidic clans, similar to how there are different deities for clerics and different schools for wizards. For purposes of this question, assume one clan favours roasted beans from Coffea arabica while the opposing clan praises the leaves of Camellia sinensis. There's a rivalry for good land that threatens to become a Range War.

The options I have found so far to prevent uninvited druids from showing up via either Transport via Plants or Tree Stride:

1. The druids kill all the vegetation nearby. This seems kinda.... anti-druidic.
2. Create a House Rule that druids can cast Forbiddance on one grove, and one druid may have only one Forbiddance spell in effect at one time. I'm probably going to do this, but not sure what else it will break.

I am assuming the other druids know where the opposing clan's grove is, because I am assuming the druids have access to Commune with Nature and thus can easily deduce the locations of the biggest coffee trees.

(1) "Casting Lock Tree from Transport Layer Attacks, the Druid uses the power of Almighty Root to walk the entire tree and encrypt each leaf with an asymmetric public key. Only those with the corresponding private key may unlock the tree for transport."

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Answer 1

Use the limitations of Travel via Plants to your advantage.

Secrecy is the first and best line of defense.

The rules for Transport via Plants suggest that you can only select a specific destination plant if it is familiar to you. Otherwise, you must specify desired distance and direction and the spell will transport you to the nearest plant of the same type as the origin plant to the location you specify.

If you are uncertain of the location of a particular kind of destination plant, you need merely designate direction and distance and the transport via plants spell moves you as close as possible to the desired location.

So the invading druid would need one of two pieces of information. First they would need to be familiar with a specific plant inside the target grove. Failing that, they would have to have enough of an idea where the target grove is that they could specify distance and direction and jump to the nearest similar plant. With this in mind, the best way to keep other druids out is to prevent them from becoming familiar with the plants there or prevent them from knowing the location. So: operational security; keep a tight hold on information.

Populate your grove entirely with plants that are tiny in size or smaller.

Transport vis Plants states that "You can enter any normal plant (equal to your size or larger)" (emphasis added). If all the plants in your grove are tiny or smaller in size, then no Small or Medium (or larger) druids can transport there. A tiny druid could still pull it off, but this guards against the main character races if they don't use magical size reduction.

Populate your grove entirely with plant creatures instead of normal plants.

This rather extreme option takes advantage of the fact that "You can't use [Transport via Plants] to travel through plant creatures."

If possible, populate your grove only with unique or extremely rare plants.

If you can have a grove with unique plants that don't exist elsewhere, or a type of plant that is prohibitively difficult to find, you can preclude another druid from getting there with Transport via Plants since they need a plant of the same type to travel.

Answer 2

Just Hire A Cleric

If this world has eleventh-level druids, presumably it also has eleventh-level clerics. Find a friendly one and pay them to cast forbiddance.

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If the druids are absolutely against hiring a cleric, a second option would be casting awaken on all their trees, making the trees invalid targets. This would be expensive.

A third option might be to wrap ropes around the trees, possibly preventing people from exiting them. It's not clear how well this would work.

Note that hostile druids can still enter the grove, for example using wild shape into an innocuous animal. I don't think it's possible to have a druid grove that is open to nature and yet closed to druids.

Answer 3

The important part isn't going to be blocking teleportation. The important part is stopping people from just walking/flying (if they have access to a 6th level spell, they probably have access to flight) in. If you ward your area against teleportation and don't deal with this, people will just teleport right next to the warded area and walk forward. Sure, you could block high-speed transport in a sufficiently large area around your grove that it would be impractical to walk, but presumably you would like to move in and out of the grove as well. Once your grove is properly fortified, including the roof, you can limit the types (Transport via Plants requires the same kind of plant for entry and exit) or sizes (such as by using Plant Growth to "open" a plant and Diminish Plants to "close" it) of plants within it.