Hello~ my well established (15yrs+) wisteria has sustained root damage from a retaining wall that was installed very close to it this past spring. It bloomed, but after blooming it didn’t leaf out as proficiently as in past years. Clearly stressed. Best course of action? Fertilizer? We’ve been watering very regularly.
Thank you
Thanks for contacting Toronto Master Gardeners. I hope the following information and links will help reassure you that your Wisteria will likely recover and thrive again. However a concern is drainage. As pointed out in the first reference below, wisteria require good drainage. If there is blockage caused by the wall and water can’t drain away the new roots might not thrive. If the soil is wet for days after a rainfall, that might be a sign of future problems. However, poor drainage is unlikely if the wisteria is on a slope. Please do not water the plant too often in your desire to help restore it. Just keep the soil slightly moist. A good application of triple mix , manure or compost (or all mixed together) would encourage new root growth (apply four or five inches deep on surrounding soil; don’t mound around the trunk bare). Also, as roots may have been severely trimmed, a single application of a commercial soluble fertilizer high in phosphorus – sometimes called Superphosphate – might be useful as it is fast acting (ref 1). Apply now. Although nitrogen found in most fertilizes is good for leafy growth, at this point your emphasis should be on helping the plant grow strong healthy roots. Vigorous leafing will happen as a result.
Here are three articles TMG published earlier concerning wisteria which you might find reassuring.