You need to be near the stems so they can grow, and also be near them when you want to produce melons after fully grown.

 

Adding to what que said: There are chunks in minecraft, which are activated when you enter them. For the melons to grow you need to be in or near the chunk they are in.

 

There are certain mods you can download to help you find them. A good one is Reis' Minimap. Can be found here!

Spoiler

http://www.minecraftforum.net/topic/482147-147-jan10-reis-minimap-v32-06/
You can customize the settings from the mod itself.

 

You can divide the x and z coordinates by 16 and if the number divides evenly it's a chunk line.

 

Both

 

I believe its around a 120 block range to be in so your crops will grow. :) Not 100% sure about that though

 

as best as I can tell, ECC has a custom setting for this, which is 3 chunks. ive done some testing and believe this to be accurate. it is the same as the render difference.

What that means is, whatever 16x16 chunk you stand in, you will load a 5x5 chunk square with you in the center. For those not so good at math, that means you can load 80x80 blocks.

Simply put, these 200x200 block farms are more or less nonsense as far as I can tell. bragging rights perhaps, looks good in trade, but terribly inefficient. Unless of course you have a well populated town with people wandering around to keep more of it loaded.

Even so. chunks extend from bedrock to the sky, so you could build numerous floors of 80x80 and I suspect you would quickly possess more floors than you can harvest.


Going a step further however... you could argue that a 3x3 chunk farm is better... the justification being that with a 4 chunk farm, even when you are in a corner chunk, the entire farm is still loaded. But this is "only" 48x48 blocks, and some may find that to be too small, too much travel time between floors. YMMV of course.

I personally grow wheat, so I do 5x5 chunks. Because wheat is more of an all or nothing harvest, I stand in the center and let it mature. Pumpkins and melons might justify a different approach.


Oh yeah, if you press F3 you will see a number in parenthesis that runs from 0-15 and repeats by the X and Z cords, this is the chunk number (there is also a number for which chunk, which you'll find is just your absolute coordinate/16). You should strive to align your farm to the boundaries of chunks, ending your farm mid chunk is bad form.

 

bauerbach,

You are partially correct. 200 by 200 farms are a little silly, except that as you are harvesting them, they do grow 3 chunks away. You have the same problem with a 80 by 80 farm as you would with a 200 by 200. When you are in the corner of the farm, only 9 chunks will be updating. Only when you are in the middle of an 80 by 80 farm will all chunks update. But, with a 200 by 200 farm, you are in the middle of a 5 by 5 set of chunks more often. Melons and pumpkins grow really fast, so a 200 by 200 farm works pretty good. A multi-floor 200 by 200 farm works even better.

I do understand chunks, fairly well. The plots in my town are aligned on chunks so that you can have either 1 or 2 chunk farms AND have some space on the edge of the farm for a building/chests.