Every crop you plant will double its yield upon harvest — one unit of corn planted in your field yields two corn units in your silo. As tempted as you may be to use up all the seeds in your silo to fill a lucrative order, don't. Plant those seeds and make sure to keep enough on hand to create the products you're going to need later. If you do, you'll have no choice but to use diamonds to buy more seeds.
Especially as your farm grows, you're going to need to constantly supply your livestock with feed — to that end, you should always have a good stock of wheat, corn, soybeans and other feed in your silo at all times.