Plants of Rosa hybrida L. cv. ‘Samantha’, grown with high or low phosphorus (P) fertilization, were inoculated with Glomus intraradices Schenck & Smith, G. deserticola Trappe, Bloss & Menge, or left non-mycorrhizal. All plants except the low-P non-mycorrhizal group had similar tissue dry weights, leaf and root surface areas, growth ratios, stomatal characteristics and P contents. The higher rate of P fertilization increased plant dry weight three-fold and leaf area four-fold in non-mycorrhizal plants, but had no effect on growth characteristics of mycorrhizal plants except for a depression of colonization levels. Under well-watered conditions (75–90% and 45–50% relative soil water content, θ), low-P mycorrhizal plants displayed greater leaf conductance (g) than both high-P mycorrhizal and non-mycorrhizal plants. Leaf water potential (Ψ) was similar in colonized and uncolonized roses. Fungal species did not differ significantly in their influence on Ψ or g.