Nearly all shrubs and trees and quite a few perennial plants have associations with mycorrhizal fungi. These relationships make plants more efficient at absorbing water and minerals from the soil. High phosphorus fertilizers including bonemeal inhibit the growth of these beneficial fungi. Root growth will increase, but it will be at the expense of other functions the plant needs to perform.
Lack of phosphorus is usually not a limiting factor of plant growth in urban soils. The only way to be sure is to get a complete soil test. Otherwise, look to other possible factors in determining why growth appears to be slow: available nitrogen, ph levels, temperatures.These are complex relationships and rushing to apply a commercial product could lead to other imbalances. I look for the quality of plant growth as an indicator of plant health, not the speed of growth. If the colors are true (not faded or unusually tinted for that variety) and the complexion is clear (not showing the ravages of insect or disease) then the plant is doing fine.
So how can we help plants struggling to overcome pest and disease pressure and be resilient in times of changing climate? Dr. Chalker-Scott is a big fan of mulch ( I am too!). My mulching guidelines are to match the type of mulch to the plants you are growing. While woody plants have their partnership with fungi, many annuals and vegetables thrive in soils where bacteria life is favored. Manure based compost works best in the veggie and flower garden and a mulch of leaves and wood chips will best nourish the soils around shrubs and trees. This is a grand paradigm shift: feed the soils, not the plants!
Some cautions about mulching from Dr. Chalker-Scott's presentation:
Sheet mulch (laying sheets of cardboard to smother weeds after mowing) may cut off the soil life from moisture and inhibit gas exchange. In my experience, watering the soil deeply and applying smaller pieces of overlapping cardboard seems to work well. Don't use this method where burrowing rodents are a problem and expect a temporary increase in the slug population.
Lasagna gardening may overload a bed with high nitrogen materials that leach nutrients. My advice is to keep the moisture content at a moderate level, as with any compost pile, by protecting it from heavy rain. Gardeners in our area have had great success creating fertile beds with a little initial effort and then have patience while the worms do the hard work.