quoting post
1- Uproot synergizes with compost, and 1 point in compost has more damage potential than 1 point of uproot.
1 point in uproot = 500 damage over 10 seconds
compost 1 = 200-600 uproot damage over 10 seconds
Compost 2 = 400-800 uproot damage over 10 seconds
Compost 3 = 600-1000 uproot damage over 10 seconds
Sorry for necroing this.
Can LO explain this to me? The damage bonus per tick is 20 (I), 40 (II), 60 (III) per every 3 units composted, right? Which means, potentially we have, indeed, 20-60 per tick with Compost I (200-600), but 40-120 per tick with Compost II (400-1200) and 60-180 per tick with Compost III (600-1800). Am I reading it all wrong?
Also, what is the buff's duration? In other words, how long does it take the composted unit counter to decrement?
Sorry missed this because I was away for a bit. Plague did a good job explaining it, but here are some more details.
Compost actually has 6 effect levels in code, but it is badly broken without uberfix. Basically you cannot reach effect level VI in ODG, and there is a bug where scoring too many kills actually resets the effect level before the 7 second timer diminishes it. 
in ODG
Compost I = Effect level I,II,III
Compost II = Effect Level II,III,IV
Compost III = Effect Level III,IV,V but there is a problem, when you hit effect V and get 3 more kills, you drop back to IV. (oops) 
In UberFix it works more like Soul Power now
Compost I = Effect Level I,II,III,IV
Compost II = Effect Level II,III,IV,V
Compost III = Effect Level III,IV,V,VI
Damage for uproot is 20 per effect level
Damage for Shamblers starts at 4 and goes up 2 per effect level. So 4,6,8,10,12.14
In uberfix, 1 point in compost is not bad, as long as you have 4 shamblers.
That gives you 40 ranged area damage potential for 1 point invested (though only 20DPS because of the low ROF on shamblers)
Compared vs Morale which gives 4 damage to all your minions
So that brings up the question; is 1 point in uproot OK if you take 1 point in compost? I think so in uberfix anyways.
The 1st point in compost is OK for Shambler damage, and that can give you 1300 damage on uproot I for 425 mana. That's pretty fantastic to weaken towers safely before you push, and you can easily take out the center archer towers this way. (fire off an uproot when you are capping the centre flag)