Sentence:  Some do also plant oziers in their eights, like quick-sets, thick, and (near the water) keep them not more than half a foot above ground; but then they must be diligently cleansed from moss, <WSD>slab</WSD>, and ouze, and frequently prun'd (especially the smaller spires) to form single shoots;.... 
Meaning of the word marked with <WSD> tags:  Mud, sludge.