Here is a basic guide to how greenhouses currently work on BatMUD. So, greenhouses are a pcity module that can be built by city administrators. When they are first built, they have only 2 tiers, but can be upgraded by a merchant to a maximum of 6 tiers. Each tier can hold 1 plant, and each plant can be picked 6 times before it has to be replanted. Besides this maximum number of picks, each herb also has a generation number. Wild-picked herbs are generation 3, herbs created with the 'create herb' spell are generation 1. Any herb that is stored in a chest or herb jar, or goes through reboot in your inventory becomes generation 0. These generations are not important for useage, but they are important for greenhouse management.

To get the most effective use from your greenhouses and herbs planted there will take several tiers. This example takes 7 tiers, which will take at least 2 greenhouses to accomplish. Also this example assumes 100% plant lore skill. Your plant lore skill will determine how many herbs you will be able to pick from any given tier per day. Your guilds matter in this as well, as druids and folklorists are more in-tune with their leafy sides, so they are able to pick more than other guilds. With 100% plant lore you can pick 2 herbs per tier per day. If you are druid or folk you can pick 3 herbs per tier per day. This example though, just assumes 100% plant lore and non-druid/non-folk.

Lets say you need barberries for some use. You wander the wilderness during the correct season and pick a barberry. You then take this barberry back to your greenhouse and plant it in your first tier, use "greenhouse help" to see a list of commands. If you now do "greenhouse view" you will see a barberry listed at "generation 3" in the tier. Now you'll want to do "greenhouse nurture <tier number>" to try to increase the maximum yield. Once you've done this, you'll have to wait for reboot, because each time you plant something in a tier, you'll have to wait until reboot to be able to start picking that tier. The next day you visit your greenhouse, you can now pick 2 of those barberries and after doing that you'll notice in "greenhouse view" that it shows (2/6) total picked. If you look at one of the barberries that you've picked, you'll see that it is now "of the second generation". Lets now plant these generation 2 barberries in your next 2 tiers and nurture them. The next day we visit our greenhouses again and we now have 1 tier with "generation 3" barberries showing (2/6) for "total picked" and 2 tiers showing (0/6) at "generation 2". Now we want to pick the generation 2 plants, all 4 of them. If we look at these barberries it informs us they are of "the first generation". Now we can plant these 4 generation 1 barberries in our remaining 4 tiers.

The next day we return to our greenhouse and can actually start harvesting! You'll be able to pick 8 barberries, 2 from each generation 1 tier, to use as you see fit. If you look at them, they do not have any generation message, meaning they are generation 0 and cannot be replanted, so use 'em up! For the following 2 days we'll be able to come in and pick 2 barberries from each "generation 1" tier. On that 3rd day, after you harvest the last of the generation 1 barberries, lets pick 4 more generation 2 barberries to replant in our generation 1 tiers. You'll have to use the following syntax to replant where it shows something already planted there (even if all herbs have been picked):
greenhouse cultivate <tier number> with barberry replace
Don't forget to nurture these newly planted barberries, otherwise you'll only be able to pick 1 after reboot. Now when we come back tomorrow, we'll have 8 more barberries to pick and use as we see fit. Keep repeating this cycle until you've used all of your generation 2 barberries, then replant your generation 2 tiers from the generation 3 tier. Once you have exhausted the generation 3 tier, you'll need to replant it from another wild-picked barberry.

Now, theres nothing preventing you from using those higher generation herbs as you would use the generation 0 ones, however unless you are just in a real pinch, and need them immediately, you are better served by planting them in a greenhouse tier and waiting to use the generation 0 herbs that you pick. Now, all that being said, from each wild-picked herb that you plant in your greenhouse, you'll end up (eventually) with 216 generation 0 herbs to use. 1 wild-picked herb yields 6 generation 2 herbs, which yield 6 generation 1 herbs, which yield 6 generation 0 herbs. So 6 * 6 * 6 = 216.

Now, lets expand this practice to be "greenhouses" instead of "tiers". It does get more expensive and requires alot of work to set up initially, but the payoff is pretty massive at the end. To do this as cheaply and as compactly as possible, you'll want to start by building a greenhouse at the ground level of a pcity street, then add exits etc to the greenhouse you just built. Head into the greenhouse and build the next 3 greenhouses upward until you are at the +3 level in the city, then head back to the ground floor and build downward until you are at the -3 level. These new greenhouses only start with 2 tiers, so to get full benefit from this you will need to have your greenhouses upgraded to 6 tiers each (see below for the requirements for this). The cost to build these 7 greenhouses in this fashion is 2,109,994 and if you aren't a merchant, you'll need to pay one to upgrade to do so, and this will likely cost somewhere around 1M per greenhouse, so another 7M on top of the 2.1M you're spending, if you go for the full 6 tiers. This system works equally well with fewer tiers, just so long as all your greenhouses have the same number of tiers.

Once you've had all your greenhouses upgraded to whatever level you want, just apply the same logic as outlined above. My method is to use the top level greenhouse (+3) for the generation 3 herbs, the next 2 levels down (+2 and +1) for the generation 2 herbs, and the lowest 4 levels (ground floor, -1, -2, and -3) for the generation 1 herbs. To use the example from above, this would take 6 wild-picked barberries and eventually turn them into 48 generation 0 herbs each day. This gives you a total of 1296 generation 0 herbs from 6 wild-picked ones.
As you can see, this method does take alot of work, and you have to stay on top of the upkeep by making sure you replant from wild herbs as necessary, but you get a great benefit from it.

Hopefully your head isn't spinning too much after reading all this and that it makes at least a modicum of sense to you. Good luck and happy farming.

Here is a list of the requirements for upgrading greenhouse tiers. Upgrades have to be done by a merchant:

Requirements to add more Greenhouse Tiers
Tier 3: -- four 5kg pieces of refined wood
        -- 25kg earth
        -- a filled jug
        -- 10kg mulch
        -- A minimum level of 25
Tier 4: -- four 10kg pieces of refined oak
        -- 50kg earth
        -- a filled cask
        -- 20kg mulch
        -- an illumium rod
        -- A minimum level of 50
Tier 5: -- four 15kg pieces of refined ebony
        -- 100kg earth
        -- a filled barrel
        -- 50kg mulch
        -- an illumium rod quality great or better
        -- two tubes
        -- a filled potion of rain
        -- A minimum level of 75
Tier 6: -- four 20kg pieces of refined mallorn
        -- 200kg earth
        -- a filled barrel of swamp water
        -- 100kg mulch
        -- an illumium rod of exceptional quality and enchanted
        -- four pipes (including blowpipe weapons)
        -- a filled potion of rain
        -- a filled potion of drying wind
        -- A minimum level of 100

The ingredients must be held or on the ground in any combination.
'mulch' is any combination of raw vegetation material or non-preserved
corpses. Both the mulch and earth can be in multiple pieces.
Rebirths count as 10 levels each for the level requirements.