In the medium saucepan, add the 10 sliced strawberries, lavender buds, 2 cups of water, and the sugar. Bring to a boil over medium heat and stir to dissolve the sugar. Reduce heat to medium-low and simmer for 5 minutes. Remove from heat, cover, and allow to steep for 10 minutes. Remove the lid and cool to room temperature.
Place the wire mesh strainer over the top of the glass pitcher and pour the strawberry mixture through it. Set aside the leftover strawberries and lavender, they are good over ice cream. Stir in the remaining 2-1/2 cups water and the lemon juice. Cover the pitcher with plastic wrap and chill in the refrigerator until very cold, at least 2 hours. Serve over ice with strawberry slices for garnish.