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To determine whether juniper mastication favors annual- or perennial-grass establishment, we compared seedling emergence, tillers, and aboveground biomass of cheatgrass and Anatone bluebunch wheatgrass. Comparisons were made among hand-planted rows between and under juniper canopies of masticated and adjacent untreated control areas at three locations in Utah. Bluebunch wheatgrass had 16% (95% CI: 11–21) and cheatgrass had 10% (95% CI: 5–15) fewer seedlings emerge per row in masticated than untreated areas (P < 0.001). However, bluebunch wheatgrass had 3.2 (95% CI: 2.0–5.2) times more tillers and 1.9 (95% CI: 1.6–2.2) times more aboveground biomass per row in masticated than untreated areas (P < 0.001). Similarly, cheatgrass had 2.3 (95% CI: 1.5–3.8) times more tillers, 2.0 (95% CI: 1.7–2.4) times more aboveground biomass, and 11.4 (95% CI: 6.3–20.7) times more spikelets per row in masticated than untreated areas (P < 0.001). This increased seedling growth in masticated areas was associated with increased inorganic nitrogen and soil water compared to untreated areas. Because mastication improves the growth of both cheatgrass and bluebunch wheatgrass seedlings, it could support dominance by either annual- or perennial-life forms. To avoid cheatgrass dominance where perennial understory cover is limited and cheatgrass propagule pressure is high, mastication should be accompanied by seeding desirable perennial species such as Anatone bluebunch wheatgrass.