Longfellow’s idyllic forest primeval is far from today’s modern urban landscape. Urban landscapes face many threats to the health of trees. Shortage of organic matter in the soil, compaction, poor soil drainage, diseased soils, erosion, unstable pH, and temperature extremes are definitely not the conditions that trees faced in the forest primeval (see table 1).How do trees in the forest primeval attain great ages, heights and diameters without irrigation, fertilizers and pesticides? The answer is that soils in the forest primeval contain a wide range of beneficial organisms that soils in the urban landscape lack. Probably the most important of these, and the most studied group of beneficial soil organisms, are the mycorrhizal fungi.