Some species are difficult to root from cuttings, because a conventional cutting cannot stay alive long enough for rooting to occur. Such "cuttings" may be grafted to a piece of root to keep them alive long enough for them to become self-rooted. This is called nurse-root grafting. The graft union is planted below the soil line (unlike most grafting), and eventually the scion becomes self rooted. Afterwards, the rootstock can either be deliberately removed or it will die off, especially in cases where the scion and rootstock are not closely related, resulting in a delayed graft incompatibility.