How to standardize different batches of a plant extract for long term work?

I have been planning to work on a plant, but I am not getting a lot of sample at a time since its been cultivated in a short place. Every 3 months I used to get sample and then after oven drying I grinded it to powder and keep it in 4 degree. Then I go for soxhlet extraction, I have been collecting plants from the same place, same land. What else should be considered during these procedure to make all my batches of sample standardized? I have to do RRLC, GC-MS, animal study with this plant.