Mountain sage grows up to 4 m and is either a multi-stemmed, densely bushy shrub or small tree. It has a pale brown bark and its branchlets are sometimes covered in rusty hairs. The wrinkly, narrow leaves are stalked, opposite and simple; medium to dark green above, much paler below, with rusty hairs, a raised midrib and side veins.

It is sometimes confused with Buddleja salviifolia, but B. loricata leaves have a more rounded base and have no stipules, just a ridge between the leaves. They are also identified by their rusty hairs. The plant is also usually a shrub, smaller than B. salviifolia and the flowers are also different.

The small flowers are in dense terminal spikes or cymes with hairy stalks and calyx. They are sweetly scented, creamy-white or yellow, sometimes with orange centres and occur in summer between October to December.

The fruit is a small capsule covered with fine, creamy-grey hairs that form dense woolly heads. The fruits split (January to March) along the flat surface when mature to release very fine, dust-like seeds.