Container‐grownPinus sylvestrisseedlings fertilized at several different levels were inoculated with vegetative mycelium of twelve isolates representing nine different ectomycorrhizal fungi. Eight isolates formed mycorrhizae of whichPiloderma croceumandCenococ‐cum geophilumwere most promising. Mantle thickness and Hartig net/cortex ratio of colonized seedlings exhibited no differences. Although unfertilized seedlings were significantly smaller than those fertilized, they were significantly more colonized by ectomycorrhizal fungi. There were no size differences between low fertilized, standrad fertilized and high fertilized seedlings. A wide array of fungus ecotypes should be tested to find a ground fertilization level at which tolerant strains can produce seedlings of acceptable size for transplantation.