Vrftjkry

Thoughts:

• Magma, lots of Magma. In essence the "surface" is very thin, perhaps 2-3 metres. There isn't soil, just basalt's and other igneous rocks. The rocks are warm to hot all the time.




• The planet is solid, no liquid iron belt protecting the planet from radiation. Sure as anything this will kill a planet. Just look at mars.

As title, what condition could prevent plant growth from below a planet surface?

Classically plants thrive on a process known as photosynthesis - they use energy from the sun's light in order to convert carbon and water into carbohydrates, and from there they get their energy.

Also classically the underground is a dark place that gets no sunlight^{[citation needed]}. That should be enough to keep plants from growin in there.

A simple solution would be to make the soil uninhabitable to organics due to some chemical. If this was intentional, by some advanced species, they could simply place a strong acid or poison in the ground. If this was part of the planet's nature, it could happen by the soil being incredibly acidic, dissolving most organisms before they can develop.

Perhaps there isn't enough topsoil to support the growth of new plant life. This was an issue on our own planet after the end of the ice age, as moving glaciers scoured large areas as they melted in areas such as northern Canada, removing the topsoil that had existed there previously. Other examples of topsoil-removing events include high winds, abnormally heavy rainfall, and exposure to intense heat and/or radiation. So long as an event such as this occurs at a regular interval, substantial plant life should be unable to grow.

If the soil contains (for whatever reason) no magnesium, then any life that existed couldn't make chlorophyll as we know it, which means no plants.

You could also try some kind of other organism that out-competes the plants, like a soil microbe that uses up resources instead of making them available.

An occasional catastrophic rad-blast would also do the trick.

A combination of a couple of other answers: A toxin that actually binds the nutrients required, preventing any plant from taking them up and using them. (This is how some herbicides work today.)

This would likely affect certain non-plants, as well (microbes, fungus, etc.).
Or, perhaps a microbe secretes the toxin so it can monopolize the nutrients. You could develop a nasty "invasive species" story from that.

Soil Depletion¹

Soil fertility depends on several factors. Changing one or more of these can inhibit that fertility:

• Sufficient soil depth for root growth and water retention.


• Good drainage


• Topsoil with proper organic matter


• Soil pH between 5.5 and 7.0


• Adequate concentrations of essential plant nutrients


• Presence of a range of microorganisms.

Disrupt any one or more variables in the above balance and your soil won't support life. For example, if some event (chemical warfare, etc.) destroys all the microbial life, then your soil won't support plants. Or make the soil acidic or basic and plants cannot grow.

Robert Heinlein touches on this briefly in "Farmer in the Sky". As part of their efforts to terraform Ganymede involves bringing microbial life to the moon to support plant growth (it's a minor point and not one of the major plot points at all, but the narrator talks to one of the older colonists who mentions that he has the best microbes).