Hello! Happy Spring! My forsythia has bloomed, but it is really sparse. (See photo) I pruned heavily after they bloomed last year, and thought it would be more full this spring (Trying to prune into cascading shape, not just haphazard all over the place) Why doesn't mine look like all the gorgeous bushes I've seen around, full and waterfalling with flowers? Do I need to cut off the thick old growth in the middle? If so all at once or over the course of seasons? Thanks!!
Baltimore County Maryland
If the thick part in the middle is dead and does not sprout, go ahead and take it and any dead material out.
Did you prune just after bloom last year or later in the season? Pruning late can take the next years flower buds off.
We would guess that the plant may not be getting enough light, which can cause stretching and scant bloom.
I pruned right after blooming last year, so that's not it. It actually gets a fair amount of sunshine. These forsythia could be as old as the house - 25 years. Or at least 10-15. (We've been here six and they were big and overgrown when we moved in.)
The very thick (maybe 4-5 inches around?) trunk parts in the middle are not dead, but they are bare until waaaaaay up toward the top of the plant, where the flowers and leaves are coming in. The trunk itself doesn't have any growth. Another friend suggested I take 1-2 of those trunks out near the ground this year and the same next year and the next, to foster fresh growth deep down in the center of the plant. Does that sound right?
Yes, the technique your friend suggests is called renewal pruning, which can help to rejuvenate old shrubs. You should cut back no more than 1/3 of the plant in one year, and then do the same in the next. Remove the oldest branches just above ground level, leaving only the younger, more vigorous branches. Read more about renewal pruning in the following publication.
Another possibility for sparse blooming could be cold damage to the buds. In some areas of Maryland, forsythias started to initiate bloom last fall when we had a very warm spell and then a quick cold snap. Even if you didn't see this off-season flowering in your shrub, it is a possibility that there could be some cold damage to the bud tissue from extreme temperature fluctuations -- and this can vary in different microclimates.
In any case, the renewal pruning should help to stimulate new growth in the shrub for future years.