Q.Can I Cut Back Overgrown Hydrangeas In Fall, They Are Mophead Variety? And When Can I Cut Milkweed To The Ground
The hydrangeas are getting too big, they are the older type, mopheads and I want to trim before the winter snow to get them under control. I also have limelight hydrangeas which also need to be reduced in size. I think I can cut them in the fall, I think they bloom on new growth. My milkweed needs to be cut back to the ground but I’m trying to figure out when the monarchs have left as I did have several leaves eaten almost bare, so I’m hoping there were caterpillars dining on them. I live in Massachusetts. any suggestions would be appreciated. Thank you, Jan Barris
While panicle hydrangeas can be pruned in the fall 2024 or as late as the end of winter 2024-2025 or early spring 2025, the mopheads may have already developed 2025 flower buds inside the stem endings so it is difficult to predict if you should. Depends on whether you do not mind zero or diminished blooms on 2025.
Another alternative regarding pruning the mopheads if you would like to preserve some 2025 blooms is to do rejuvenation pruning. To control the size of an unkempt or overgrown mophead shrub, you can begin a 3-year long rejuvenation pruning program that prunes the shrub while the plant is fully dormant and leafless (usually in winter). This allows you to see the stems' skeleton clearly without the foliage still attached. First, begin by visually dividing and then tagging the stems into 3 groups as you wish, and on each winter, prune all the way down the stems belonging to a single one of those groups and leave the other two groups of stems unpruned. Ensure that the unpruned groups include stems with visible 2025 flower buds at the ends of the stems. These buds are found immediately above each pair of leaves.
For example, on the first winter of a mophead hydrangea that is being rejuvenated, you could group the stems according to stem length. Group 1 could consist of the longest stems. Group 2 would consist of the mid-sized stems. And group 3 would consist of the smallest stems. Next, make sure that the groups that will remain unpruned always have stems with visible flower buds; if they have few stems with buds, swap out stems between the groups. Decide in what order to prune, such as prune group 1 only in winter one, prune group 2 only in winter two and prune group 3 only in winter three. To wit: in winter one, cut down all of the stems in group 1 and leave the other two groups of stems untrimmed; in winter two, cut down all of the stems in group 2 and leave the other two groups unpruned; and in winter three, cut down all of the stems in group 3. Resume normal pruning from this point forward. The stems could also be grouped in other ways such as by their location: front, middle, back; left, middle, right; etc.
Since pruning is an activity that can trigger leaf out and new stem growth, this type of pruning is best done when the shrub is fully dormant in winter. If you rejuvenate a hydrangea that blooms on old wood or that blooms on both old and new wood, this type of pruning can reduce blooms in spring but, since you only cut 1/3 of the total number of stems each winter and since you always aim to keep some stems with flower buds amongst the unpruned groups, rejuvenation pruning should not entirely eliminate flower buds for a complete year.
In Massachusetts, monarch butterflies typically begin their migration south in late August/September, with the majority leaving by mid-October. To avoid cutting back your milkweed while caterpillars might still be feeding or while monarchs may be laying eggs, it is best to wait until much later while also ensuring you do not still see any remaining caterpillars (so wait until November may be safer). By that time, most of the monarchs will have left for their migration.
