There are a few things you could try if you want to produce thicker asparagus. First and foremost, give your asparagus lots of room to grow. Crowding can cause spears to become thinner. Also, make sure to keep the soil wet. Water is a favorite of asparagus! You may also try adding compost or other organic materials to the soil to help your asparagus grow. Finally, patience! Asparagus can take several years to mature, so do not be disheartened if you don't see thick spears straight away.