Great question Mara. TUB does not directly specify how plants know to do what they do. What they do tell us is that plants are alive, they have “life”. As far as I can tell, life and mind go together like soup and sandwich. All life is directed, in some way or another, by mind. Evolution is mind-directed, and the adjutants, we are told, animate life and drive evolution.
If that is true, then plant life could be considered “mechanical mind”, which is primarily pre-adjutant and ministered to by the Physical Controllers, according to this quote:
42:10.3 1. Preadjutant-spirit minds. This level of mind is nonexperiencing and on the inhabited worlds is ministered by the Master Physical Controllers. This is mechanical mind, the nonteachable intellect of the most primitive forms of material life, but the nonteachable mind functions on many levels beside that of primitive planetary life.
However, we are also told that the first adjutant, the spirit of intuition, is the only adjutant that makes contact with “mechanical mind,” which is a little confusing.
36:5.6 1. The spirit of intuition – quick perception, the primitive physical and inherent reflex instincts, the directional and other self-preservative endowments of all mind creations; the only one of the adjutants to function so largely in the lower orders of animal life and the only one to make extensive functional contact with the nonteachable levels of mechanical mind.
I suppose the answer lies in how you interpret all these quotes. What is mechanical mind? Do plants have it, or are they subject to it? Or, are plants purely mechanical energy, without mind of any kind, yet responsive to the mind of the Physical Controllers, as the next quote suggests?
65:7.5 The seven adjutant spirits do not make contact with the purely mechanical orders of organismal environmental response. Such preintelligent responses of living organisms pertain purely to the energy domains of the power centers, the physical controllers, and their associates.
118:8.1 In the time-space creations, free will is hedged about with restraints, with limitations. Material-life evolution is first mechanical, then mind activated, and (after the bestowal of personality) it may become spirit directed. Organic evolution on the inhabited worlds is physically limited by the potentials of the original physical-life implantations of the Life Carriers.
I’m inclined to think that most plants respond to mind, but not to adjutant mind. Right now, and subject to change, I think the adjutants minister primarily to animal life and the Physical Controllers to plant life. There are primitive, non-teachable, mechanical levels of animal life, such as protozoa and my ex-husband. Bacteria and fungi, however, are plants. (Sometimes I think bacteria do have a mind of their own though . . . just sayin’ . . . they can be stubborn little critters. Then again, so can weeds.)