In the heat of the summer, some yellowing due to all forms of heat stress is expected. Down here for example, we are still in summer mode; we just hit 95 degrees yesterday.

Buuuuuuuuuut in northern IL at this time of the year, I expect hydrangeas to be in shut down mode. Yours are obviously ahead of the neighbor's hydrangeas but not a big deal. The green leaves will then turn yellow, brown out and fall down. Or if a dip below freezing happens, some green leaves will actually look dark green ugly and then turn brown. You can let the brown leaves drop down on their own if you have no fungal issues. If you do have fungal issues, you can throw them into the trash instead. You can leave the spent blooms for Halloween/winter interest or deadhead them whenever you want.

As usual, maintain 3-4" of mulch in preparation for winter and -still- keep the soil as evenly moist as you can for now. Once the plant goes dormant, you can reduce waterings down to once a week or once every two weeks but stop waterings when the soil freezes.

This year is expected to be warmer than normal due to El Nin~o on the northernmost states. They say it will be the strongest one in 50 years so maybe try to read up on what to expect weather-wise in IL. Wild temp changes may "awaken" some dormant plants and this would especially negatively affect any mopheads, oakleaf and lacecap hydrangeas. Their stems and invisible flower buds may get zapped if not winter protected. So if you have any of those, consider using winter protection.

VS, being a paniculata, will not need winter protection as panics care usually hardy to Zone 3 and develop invisible flower buds in late Spring or early Summer... but I mention it just in case you also have some of the other hydrangeas.

Thank you! I was getting nervous, as people with neighboring hydrangea plants aren't exhibiting this same yellowing, but their bushes are also several years old and much larger. As I mentioned, mine are less than 1 year old.

At this time of the year, if you are still watering properly, assume that yellowing in paniculatas and in some mopheads & lacecaps too is related to dormancy.

Some hydrangeas will go dormant ahead of other hydrangeas so, I would not worry just because others have not caught up with your five VSs.

Interestingly, oakleaf hydrangea leaves will put on a "nicer" Fall show. Their foliage turns to red/orange/purple/brown shades that looks very nice at this time. A few macrophyllas have leaves that turn those colors too but most of the macrophyllass that I see around just turn their leaves yellow. Oaskleaf hydrangeas (H. quercifolia) are hardy to Zone 5.