Fresh, timely updates about what is going on at the farm are important and compelling for customers, but extremely hard to maintain in the busiest part of the harvest season. There are a number of strategies to make this happen including blocking time out of your schedule or writing content ahead of time.
However, I think one of the most important things to realize is that short is okay for your blog updates. A timely photo and a few lines of text may be more interesting to a customer than a 1000 word essay on integrated pest management. I think there is a place for longer form copy on, for example, growing practices, but that is in the "static" part of your website that does not change all of the time.
People are in a rush to read your updates most of the time, so the extra effort to write a long essay each week may be wasted. Keep it brief and compelling.