bro, ill let someone else answer the fert question. if the strain is mostly sativa, ive noticed that the buds dont get that big, at least for me. my indica plant had huge buds. the trichs are the best bet to tell when they are done, most indica strains are around 7 to 9 weeks, sativia's can take 10 to 14 weeks. here a pic and a chart. you need to get a scope, they have them at radio shack for less than $15.
When to harvest
Trichomes are small appendages that look like hairs. They are produced by marijuana, and other plants. Female marijuana plants produce certain trichomes that are a rich source of THC. These trichomes can be found in their largest concentration on the buds. They start out clear, turn a milky color, then turn amber (light brown).
The trichomes in picture 1 are clear. After the plant has flowered for a few weeks, the trichomes start to turn a milky color (picture 2). After a few more weeks, they will be totally milky in color. In the later stages of flowering, trichomes will turn to a light brown color (picture 3). The amount of time required to get to this point depends on the marijuana strain and the growing conditions.
In picture 2 you can see the stems have started to turn from a clear color to a milky translucent color. For maximum THC content and a more cerebral and energetic high, harvest your plants when a majority of the trichomes on the plants in your garden are a fully milky translucent color.
You can wait until most of the trichomes have started to turn amber, but the resulting marijuana will produce more of a sleepy body stone than it would if plants were harvested earlier. The trichome in picture 3 is about 90% amber, with just a trace of the milky translucent color it previously possessed.
After the trichome is fully amber in color, the THC starts to degrade. This makes it very important to harvest marijuana at the time before a majority of the trichomes have attained a total amber color. If not, the marijuana will not be as potent as it could have been.
Based on that information once trichomes have turned milky white maximum THC levels have been reached and remain at that level until fully amber. So any time between filly milky white and fully amber is the peak THC level and when each person needs to decide when to harvest in that period of time is solely based on each individuals personal preference in high or stone of combination of each.
In short the prime time to harvest is variable based on personal preference as long as it is between when the trichomes have turned fully milky white and when they are fully amber.
　
Pure sativas and highly predominant sativas reach maximum THC potency when the trichomes are still clear. It will max out just before clouding occurs so it is best to harvest them at the first signs of clouding.
But many people call any cross that is over 50% sativa a sativa and unless a strain is upwards of 80% sativa or higher you would want to wait until you see mostly cloudy trichomes with some amber trichomes and possibly with a few clear trichomes left.
