A good ratio of clay soil to organic material is roughly 50/50%. You said you have organic fertilizer if this is composted materials from the garden, it is great. Peat moss…be careful and do not add too much. Put peat moss in a bucket and fill the bucket with water. Where does the peat moss go, to the top. It is hard to moisten clumps of peat moss. It is great if it is mixed well with the soil and compost and not added as layers. Do not make the soil so luxurious that the plant will not try to accumulate itself to its home. It will eventually have to grow in the soil around it as it gets larger and the roots expand. Do not go over the 50/50% and maybe even a little below if working with a Texas native.