Question
hi
I took cuttings from my dad's hydrangeas a few years ago.  I live in zone 5
(Green Bay, WI) and I planted them next to my house, facing the east.  They
have grown nicely and get flowers. But I'm noticing now that there's gaps.  
There are 4 separate plants. The 2 center ones get few flower heads and
those mostly stay unopened (making them look like the lacey ones).  The
others look great!  I can't figure out what could be the difference between
them since they came from the same place. Any ideas?
thanks.

Answer
It took me some time, but I think I've got it figured out.

Now that it seems so obvious, I don't know why I didn't think of it in the first place.

How far apart are these shrubs now?  You mention that they are planted in a row, next to one another, with the ones in the middle underperforming, while the outside pair are sailing smooth.  You've probably heard about the naturally occurring, soilborne Fungi called Mycorrhizae that colonize plant roots and deliver moisture and nutrients to the plant.  These specialized Fungi make contact with plant roots and if it's the right kind of plant, they develop more and more hyphae to obtain more and more nutrients for the companion plant.

Hydrangeas, like other shrubs, respond positively to these very helpful Soil Fungi.  To get the Fungi to work harder at their job, the host shrubs release 'exudates' through their roots, especially delivering photosynthetically derived gun.

But if you are limited in the Fungi you can obtain -- if the Mycorrhizae are restricted in any way -- you deprive the roots of highly specialized nutrient generators.  If the roots are restricted,
the photosynthetically derived organic Carbon that gets Fungi to sign up for work with the Hydrangea roots.

And I think that may be what's happening here.

Avoid cultivating in the area of these shrubs, to allow the Soil to mature.  Don't use ANY chemical fertilizer.  To deliver better conditions, put down aged Manure and well aged Compost right around the drip line as well as within a generous radius of the shrubs.  And watch what happens.

If these are colored Hydrangeas and you are looking for strong Pinks or Blues, back off on the pH-changing substances.  They're too toxic for the Hydrangea-friendly Fungi.

Thanks for writing and please keep me posted.'

THE LONG ISLAND GARDENER