I bought three different lilac varietals (French Red, deep purple and a variegated variety) in the spring of 2016 - they arrived as small suckers. I kept them in pots for a couple of years, and finally put them in the ground in the fall of 2019. Since then, they have gone NUTS putting on size, but have yet to set buds. Conversely, the sucker I planted from a neighbor's well-established classic purple lilac has not put on much size, but it has set buds faithfully each year. They are planted together so conditions are more or less the same for all three. Is there anything I can do to encourage blooms? Or do I just need to be patient?