In the Heroes of Might and Magic series, a creature's growth is the number of units of it's type that are produced weekly in a recruiting center (usually a town). Depending on the game, the growth can be influenced by several factors.
Heroes of Might and Magic I[]
In Heroes of Might and Magic I, the growth is not proportional with the creatures' relative strength, and contributes to the game's lack of balance. The stronger a creature is, the lower its growth is expected to be, but this happens in Heroes I to an insufficient extent. The Well makes matters worse, because it increases all the growths in a town by +2 (indiscriminately of creatures' relative powers).
Weeks and months can randomly influence creature growth. The week of a particular creature causes that creature's dwellings to increase its growth by +5 for the week, while the month of a particular creature causes that creature's dwellings to double its growth for the week. Additionally, all unrecruited creatures of this type will see their number doubled, and wandering monsters of this type will be added on the map.
The infamous Week of the Plague causes dwellings to cease producing creatures for the entire week. Additionally, all unrecruited creatures have their numbers reduced by half.
Heroes of Might and Magic II[]
Creature growth in Heroes II works very similarly to the growth in Heroes I, even including the well which increases the growth of all creatures by two, regardless of their strength.
Heroes of Might and Magic III[]
Flagging external dwellings in Heroes III has an extra effect – these structures not only offer creatures for recruitment on the spot, but boost the in-town growth of their creature type by +1 (this effect stacks with bonuses granted by all flagged external dwelling).
The Well has been eliminated, and as a substitute, the Fort has been introduced – a purely military building, the Fort is required for the building of every single dwelling in the game. The Fort can be upgraded twice (first to Citadel, second to Castle). Each of these upgrades increases creature production in the town, the Citadel boosting all base growths by 50%, and the Castle doubling base growths. These boosts exclude flagged structures or other like bonuses.
The Grail increases all the base growths of its host town by 50%. The Statue of Legion (introduced in Heroes III: Shadow of Death) does an even better job by increasing growth by 50% in all the player's towns. Again, flagged structures or other like bonuses are not considered when calculating the new growth rates.
Horde buildings are present, like in Heroes II.
Heroes of Might and Magic IV[]
In Heroes IV, the Fort/Citadel/Castle buildings do not modify the number of creatures generated. External dwellings also do not increase in-town growth, though they can be accessed via the caravan system as a way to generate additional units in a town. Additionally, the "month of" creature events do not grant extra creatures, though the named creatures will spawn on the map as neutral armies.
The Nobility skill affects growth, adding 10% extra creatures growth per skill level. To get this benefit, you must install a character with this skill as the governor in the town to be modified. Finally, in the Stronghold, the buildings Festival of Life (Grail required) and Breeding Pens influence creature growth. For the Festival of Life building, it increases the growth of all towns by 25% and the town in which it is installed by 100%. The Breeding Pens provide 50% growth in the town where it is built. Note that these features stack, so it is possible to have very high growth with both buildings and a grandmaster of Nobility installed as the governor.
Heroes of Might and Magic V[]
There aren't many features changed, as most features have been added from Heroes III.
Might and Magic Heroes VI[]
In Heroes VI, growth depends on buildings – Fortifications grant +1 growth to all creatures; building all three provides a total of +3 growth to all creatures. Also, if a creature dwelling has been built, it grants extra growth points as well. When external dwellings are flagged, they add extra growth points to the owner's town(s). Finally, each town can access the recruitment pools of all towns and external dwellings at once, eliminating the need to recruit from each town and dwelling individually.