When to Fertilize Shrubs | Gardening Advice
The flowering shrubs in our landscape don’t give us much bloom in our sandy soil, even though we maintain sufficient moisture. Should I use fertilizer? When is the best time to fertilize shrubs? — K.F., Manchester, NH
Early autumn in New England is generally considered an ideal time to apply fertilize shrubs and trees used in landscaping. This is the season when colder temperatures and shorter days slow top growth, but warm soil continues to enable roots to grow. Fertilizer taken up by active root systems builds strength to support next year’s flowers, fruit, and top growth.
It’s best to choose a high-organic fertilizer. Fertilizers with a strong organic content cost a bit more than inorganic types, but they produce superior results because their nutrients are absorbed by roots systems more gradually. During fall, it is best to use a lower nitrogen formulation with a higher middle number (like 5-10-5, which signifies five parts nitrogen, 10 parts phosphate, and five parts potash). Phosphorus encourages strong root growth, which helps improve flower bud set. A high-nitrogen type may encourage excessive top growth that could be damaged by upcoming colder temperatures. Consult with the experts at your local garden center for recommendations about the best formulations to suit your specific conditions.
I’ve heard that fertilizing shrubs and trees in the fall is a good idea. Doesn’t applying fertilizer this late in the season cause winter damage? P.T., Falmouth, ME
In New England, autumn is an ideal season to apply fertilizer to most hardy plants (this is when most nurseries do it). Cold temperatures have stopped the aboveground parts of most plants from growing, allowing nutrients to be readily taken up by roots and stored for stronger growth when spring arrives.
You can expect advice from experts at a local independent garden center to be very accurate — they have specific knowledge about your area, backed up by years of experience. Ask for fertilizer formulations that match the type of plant (evergreen, deciduous shrub, perennial, etc.) and apply it at the recommended rate. Bear in mind that your local conditions may require different approaches than the one-size-fits-all tips we see on TV gardening shows or read about in magazines.