Some efforts made yet this fall in the garden can help save you time next spring. Although we have had some hard frosts already, there are some plants out there that should be cut back and/or entirely removed this time of year as they will be nothing but problems for you next year. Many of our garden weeds are still green and easily identifiable out in the gardens. The invasive garlic mustard (Alliara petiolata) is still very green and can be targeted right now. Much of the garlic mustard you see now will be the "blooming wave" next year as this plant is a biennial and blooms (thereby dropping oodles of seed) the second year from germination. We'll hand dig it when we see it and if we get another warm day above 50 degrees F, I'll spray a bit of Round-Up on these target plants as it will still have time to kill off these plants before snowfall (hopefully). As you're cutting back your garden, anything that elicits a "Hey, I didn't plant this" should be followed by the action of immediate removal, saving you time and headaches when diverse spring duties might be more of a distraction. The top image is the fall appearance of garlic chives (Allium tuberosum) which were blooming in August and September with beautiful umbels (rounded flower clusters) of white. However, these culinary chives should be deadheaded before they go to seed as seen above and more specifically to the right. Look at all those seeds ready to fall and germinate next spring. With these potential seed clusters not removed in a timely fashion and left to drop seed, the end result next spring is a solid mass of grassy babies throughout the garden that will need to be culled, thinned and dealt with immediately. There are many other plants/perennials with similar challenges. While they have beauty and/or function in the garden, those rampant re-seeders should have flowers removed prior to seed set/seed drop to keep control of unwanted spread.
Now is the also the perfect time to target the notorious European buckthorn (Rhamnus cathartica) which has invaded a good portion of the Midwest and Eastern United States, particularly woodlands. We have some around the periphery of RBG and will find invaders that have disguised themselves well in the gardens proper. The woodlands around our area are thick with this non-native woody plant that has a competitive advantage in our woodlands in that it leafs out earlier and is tolerant of full sun to full shade. When I worked in MI, I observed woodlands that were so thick with European buckthorn, you couldn't walk thru them. The floor of those forests, instead of having native perennials, ferns, etc, were barren as there was almost no light due to the understory of buckthorns, This solid mass also outcompetes a native understory of trees which is what will replace our larger desireable trees as they die and leave an opening in the woodland canopy. There are lots of articles on this notorious tree but suffice it to say that it is a Thug with capital 'T'. However, this time of year, buckthorn becomes very conspicuous as it retains green leaves well in to December so as I type, you could walk thru a woodland (or your garden) where most deciduous trees and shrubs have dropped leaves or are in the last stages of fall color and note those specimens with green, glossy leaves. See the picture below which was taken at RBG yesterday. The desireable shrub, an arrowwood viburnum (Viburnum dentatum) has lost most of its leaves although you still see some yellow ones to the left. The stems (marked with blue tape) that have green leaves are from a buckthorn that has "hidden" in the midst of this shrub for years as it blends in well during the summer. That buckthorn was planted by a bird that ate the black fruits (drupes) of a female buckthorn and pooped them out while hanging out in that shrub. Bird dispersal, far and wide, of this non-native is what has given it such a wide range of invaded territory. Now, this multi-stemmed shrub is so entwined with the viburnum that digging it out is not a real option. By the way, hand digging out buckthorn is a monumental effort and the wood is extremely hard and difficult to cut. The branches also have terminal spurs which for all intents and purposes, can be considered "pseudo thorns" as you try to remove and dispose of the wood. Be careful and wear gloves and eye protection. Steel toe boots would not be overkill either.
This is how we deal with a situation like that below and anywhere we target the conspicuously "green-leaved" and easily located European buckthorn this time of year. Cut the primary stem/trunk as low as you can and immediately paint on full strength, concentrated Round-Up, right on that fresh cut. Be very specific with painting on the Round-Up as you don't want to damage surrounding plants. Let it soak in that fresh cut, then paint it again. We have had a high percentage of success with killing off the entire plant with this fall approach. In the situation pictured below, this approach is warranted so as not to harm the "sheltering plant". However, we also do it in all removal situations (even for larger buckthorn specimens) as we don't have the time to hand dig the roots. Smaller buckthorn seedlings can frequently still be pulled out if the ground is damp enought. Otherwise, cut and paint. Cut and paint. Processing the above ground remnants is challenging too and be wary of the females which are still showing fruits (drupes) that hungry birds will continue to nibble and "poop disperse". Good luck.