Although most investigations of clonal plants have focused on negative aspects of interactions with neighbors, some studies have shown positive effects of clonal plants on other species, especially clonal plants with a compact, or phalanx, growth habit. For example, several plant species have been observed to grow directly upon tussocks of the freshwater rush Juncus effusus L., and the phenology of those species appeared to correlate with seasonal dynamics of the Juncus canopy. The present experimental study was conducted to enable distinction among four aspects of the Juncus tussock microhabitat: 1) collapse of the Juncus canopy, typical of summer conditions, 2) springtime pre-collapse erect architecture of the Juncus canopy, 3) availability of a living tussock platform in the absence of a canopy, and 4) simple physical provision of an elevated, organic surface for colonization in the form of artificial rooting platforms. Several species responded to particular features of the Juncus effusus canopy; three of those species, Boehmeria cylindrica, Leersia oryzoides, and Lonicera japonica, were identified as facilitated species in previous research on facilitation by Juncus. Particular features of the Juncus tussocks that appeared to correlate with increased cover of colonizing species were Juncus canopy height, tussock basal diameter, and relative water depth atop the tussock. Thus, results of this experimental study support conclusions from prior work on facilitation by Juncus effusus and other tussock-forming species regarding the importance of tussock physical structure in providing sites for plant colonization in freshwater wetlands.