Fair enough! We can compare end results.
For the spores, I think I'd look to the vrock for inspiration...
Spores (Ex): A vrock can release masses of spores from its body once every 3 rounds as a free action. The spores automatically deal 1d8 points of damage to all creatures adjacent to the vrock. They then penetrate the skin and grow, dealing an additional 1d4 points of damage each round for 10 rounds. At the end of this time, the victim is covered with a tangle of viny growths. (The vines are harmless and wither away in 1d4 days.) A delay poison spell stops the spores’ growth for its duration. Bless, neutralize poison, or remove disease kills the spores, as does sprinkling the victim with a vial of holy water.
*SNIP*
I think the vrock's model works fairly well, except I'd drop bless and holy water (as the plantman isn't inherently evil). I agree with adding a Heal check. I'm not fond of the limitations by creature types (other than for the "create spawn" portion).
Half of the plantmen in a group have 1 or 2 HD, while 25% have 3 or 4 HD. The rest are 5 or 6 HD (equal chances). For every 50 plantmen, there is a sub chief with 7 or 8 HD and 1d4+1 bodyguards of 5 HD each. Each tribe of plantmen is led by a chief with 10 HD and 2d4 bodyguards with 6 HD each.
Plantmen co-exist well with plant and fungus life. They often use shriekers to guard their lairs, and plant men native to the lair can pass by those shriekers unnoticed. Russet plant is usually found in the vicinity of a plantman lair as well.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.