Watering the surrounding area is a good idea in general to promote root development —depending on the soil cucumbers can spread roots either wide or deep, so this shouldn't be the peimary issue here.

Best guess for slow initial growth would be a combination of temperature and overwatering, the latter beinh indicated by the pale leaves. Test the soil moisture a few inches deep with your finger.

Once they start developing better, start adding a source of nitrogen to the water every other day, which will help their growth.