|About 5 years ago we planted a row of 8 Northern Sun Forsythia shrubs along our southern properety line. 7 of the 8 have grown well, though they have seldom bloomed well. We never trim them until after the blooms are done. We planted this variety because of their reported hardiness in our Northern Illinois zone 5 conditions. We wonder why the blooms have been so disappointing. The other problem we have is with that 8th bush, which is in the middle of the row. We have replaced it every spring because it does not survive. It grows well at first, and they we notice it begin to die branch by branch. The area is well drained and we water sufficiently to keep it mist enough. The soil is sandy/gravely with supplements added to enrich the soil. We do not fertilize them. Any suggestios or ideas are appreciated.|
|There are only a few reasons for non-blooming in forsythia. The first is pruning; forsythia blooms on wood produced the previous season so your practice of pruning after bloom is finished is the right approach. This gives the plant all summer to produce flowering wood for the following year. The second common cause for non-blooming is inadequate sunlight exposure. Make sure your forsythia receives all day sunshine during the summer months. Finally, over-fertilization will cause lots of green growth at the expense of blooms so don't fertilize your shrubs.|
If you've repeatedly replaced a shrub, I'd suspect a problem with the soil. Since you're sure the soil drains well, you might want to have the soil tested for residual chemicals. Aside from the above, I can only encourage you to keep trying. Forsythia is such a beautiful plant that its worth the extra effort.
Best wishes with your landscape!