Get Out the Chainsaw
To rejuvenate, some plants must have their stems pruned near the ground. The plants I’m describing each have a large root system, so the crowns will send up numerous new stems.
The butterfly bush (buddleia), for example, should have all its branches cut down to within inches of the ground every year in early spring. Severe spring pruning encourages the development of strong stems that will flower more profusely. I use a chainsaw to prune my buddleia at the beginning of March, which encourages the plant to flower sooner.
Forsythia needs proper annual pruning. I make it a habit to prune one-third of the branches on my forsythia plants every year as soon as the petals fall. I start by removing the older stems with gray bark. I then remove all branches originating from the base that are smaller than a pencil in diameter as well as branches that are arching toward the ground. If you allow arching branches to touch the ground, they will root, and before you know it your mother plant will have produced daughter plants, and soon you will have more forsythia plants than you know what to do with. Forsythia grown without pruning will often die because of over-crowding of the branches.
If you’ve fallen behind on the job, prune both species close to the ground as soon as most of the flower petals have fallen. If you prune now, new vigorous stems will emerge from the roots within a few weeks. Allow these stems to grow all summer long without further pruning. If the plants are in good condition, the new stems will grow to a height of five to six feet by mid July, and their bark will be brownish-yellow.
Weigela also blooms better if one-third of old branches are cut out each year. Use the same approach as described for forsythia, removing the biggest woody branches. Shaped forsythia plants look awful, but weigela can be pruned for size, branch by branch as far back as one-third. Cut them back to a point where two branches meet. Untended weigela can take hacking, cutting all branches back to about four inches above ground level.
Privet hedges that are old or have not been properly shaped often lose their bottom branches and leaves, making them appear top-heavy. Such hedges can be rejuvenated by simply cutting all of the stems very close to the ground and allowing new young stems to grow. The earlier in spring you prune them the better.
The training of a new hedge begins as soon as the majority of the stems have grown 12 to 16 inches. To build a uniform hedge, pull a string the length of the hedge 10 inches above the ground, and prune away all stems that are above the string. Repeat after the new stems have grown another 12 to 16 inches, this time cutting them back to 20 inches above the ground. Continue until the hedge has achieved the desired height.
To retain foliage from top to bottom, always shape the hedge so that the top is narrower than the bottom. If you allow the top of the hedge to grow wider than the bottom, the top will shade the lower branches, which will lose their leaves.