The secret to this mystery seems to be that the non-blooming hydrangeas have much lighter green leaves. This indicates a lack of nitrogen and other nutrients. Poor drainage or compacted soil means not enough oxygen in the soil for microbe activity. Another guess is that the two weak hydrangeas had some damage to their roots when you planted them into the ground. Did you just recently add all four plants to the garden within the last two years? Sometimes a potted plant with crowded roots will not adjust and spread their roots outward into the soil to find nutrients. I suggest giving a tug on the non bloomers and see it they have a compacted root system. You can dig up the entire rootball and tear it apart a bit to tease the roots outward. At this time you can also loosen the soil in the planting area and check to see if there is clay or poor drainage. Spread Osmocote over the topsoil near the roots so that the leaves will green up with the addition of the nitrogen in the Osmocote. Water the plants well after you dig them up and keep the soil moist all summer while new roots are made. I predict all four plants will be in flower next summer. Keep growing, Marianne Binetti