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How do I backfill my planting holes for hydrangeas?

3 years ago

Hello!

I am planting six Nantucket Blue hydrangeas in Dallas, TX (8a). They will all receive dappled shade throughout the day courtesy of being under two large live oak trees. I hope the dappled shade will protect them enough to survive our hot summers. I will have drip irrigation set up for them, and I already purchased the 5-gallon plants from a local nursery but have not put them in their holes yet.

There's a lot of clay (alkaline) in Dallas, but it's not especially dominant or heavy in the beds that I'm putting the hydrangeas in. There are lots and lots of worms, so that's good, and there is a good amount of clay, but there's also some more workable soil too. The holes I dug are 10-12 inches deep, and are 3 feet wide and 4, 6, and 8 feet long. In the 4 ft and 6 ft holes I'm planting one hydrangea each, and in the 8 ft holes I'm planting two.


I see some conflicting advice regarding backfilling holes with NATIVE vs AMENDED soil for shrubs. Gardeners' World says in their show to backfill with only the NATIVE soil you took out so roots are encouraged to spread and avoid the issue of creating pot-like conditions where water might drown them, especially in clay soil. Neil Sperry, a local source of expert advice, says for hydrangeas to completely replace dug-out soil with a mix of half peat moss and half pine bark and mound it about a foot above grade as well, to discourage wet feet. Neil's recommendation seems too light on food for the plants, right? I also found thistlewoodfarms.com which has a page for hydrangeas in Texas and I am tempted to follow their recommendation, which is to replace the native soil with peat moss + potting soil + pine mulch.


Summary of what I could use help with:

  1. Should I backfill with the unamended native soil, or should I get rid of the native soil and put in an amended mix?
  2. If amended is better, what recipe should I use?
  3. I want a mix of blue and pink blooms. In Dallas, I'm told that by default the blooms will be pink once they reach our alkaline clay soil, and I'll have to work hard to achieve blue blooms. My current plan (unless you advise me otherwise) is to backfill with peat moss + azalea soil + pine mulch + sulphur, and add aluminum sulfate on a schedule, if needed, to get blue blooms. I figure eventually some of the blooms will turn pink due to our alkaline natural soil around the beds and our alkaline tap water I'll be using to water them. What advice do you have to try for multi-color blooms?

Thank you all SO MUCH! I'm hoping these plants will help my wife and I be reminded of the amazing hydrangeas in New England!

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