My experience with heather is that they don't root readily from cuttings that has 'old wood', to have that part to root successfully, it has to be still attached to the parent plant. I my work, which is in heathland, I tend to weigh down a branches with stones and make sure they are in contact with soil or partially buried...then later on, months later I check if the roots have formed and come late autumn-winter when the ground is constantly moist I dig the rooted branches up, cutting them off from parent plants and transplant it to new places.
And like already mentioned..it does help if the ground around planting hole Is cleared from competing growth.
Now green tip cuttings are much quicker to root but those need to be rooted in trays/pots and looked after a year before planting. If you treat them like 'commercial' cutting giving them gentle heat from propagator they will root in weeks and transplanted into individual pots to grow on larger.
Which ever way you go with heather...they are quite slow to root and to establish>to spread.
You could also try seed casting> clear some ground from grass...rip 'old'/faded flowers off from plants ..with hopefully some seeds still in..and sprinkle them about ..if you smoke the seeds before sowing (do not heat them!)...the chemicals in the wood smoke have properties that will enhance germination success rate. You kind of imitate what happens to heather seeds with wild fires in nature. Just collect loads of flowers/seeds...and place them in tray..bag..etc..nearby small smoking fire and let them 'choke'..that's all to it.