Brown azaleas: Are these shallow-rooted plants victims of a hot, dry July?

Bill in Springfield writes: “My azaleas had been doing well, but I’m seeing light brown taking over the leaves. I have been watering them and keeping an eye on them. Any advice?”

Yes, Bill. Azaleas and rhododendrons are very shallow-rooted, which contributes to their being some of the thirstiest plants in the landscape — especially if they’re in full sun and even more so with the scorching temps and lack of rain we’ve been enduring.

So your problem could simply be lack of adequate moisture. Your statement, “I have been watering them,” could mean many things. The short, frequent waterings that many listeners confess they do are useless; you want to provide long, deep soakings. Let a hose drip at the base of the plants for several hours in the early morning at least once a week during normal weather when rain is scarce.

Up that to twice a week during really hot, dry times, and every other day during the kind of merciless weather we’ve been enduring.

Plant food does not come in a little green box

Bill in Springfield writes: “My azaleas had been doing well, but now I’m seeing light brown taking over the leaves. Should I treat them with some nutrition, like Acid Miracle Grow?”

Yes Bill, you probably should “treat them with some nutrition,” which excludes the chemical fertilizer whose name you just mangled a bit. The last thing any plant needs in hot, dry weather is to be doused with the concentrated salts in heavy-handed chemical fertilizers.

Instead, consider trying the product that came first for this purpose: Holly-Tone. It’s been around for over half a century (since 1949, I just learned from the folks at the parent company Espoma). It’s an all-natural fertilizer, and it increases the soil acidity of acid-loving plants like azaleas and rhododendrons. (It does this using elemental sulfur instead of the highly explosive ammonium nitrate found in similar chemical products.)

Apply as directed and cover with soil or compost to help get the natural nutrients to the plant faster.

Azalea and rhododendron 101

The leaves on Bill’s azaleas in Springfield are turning brown.

  • The most likely cause is inadequate watering. When the weather is hot and rain is scarce, azaleas and rhododendrons need our help. Let a hose drip gently at the base of each plant for a few hours in the morning twice a week; thrice if the plants don’t get afternoon shade in this heat.
  • Next is the soil not being acidic enough — although that generally results in yellow leaves. No matter what, it couldn’t hurt to use a natural product like Holly Tone to feed the plants and adjust their soil pH.
  • Or mulch them with an inch of milled peat moss (for acidity) topped by an inch of compost (for the ultimate slow-release natural feeding).
  • And finally, these are the last weeks you can safely prune these and other spring-blooming plants and not affect next year’s flowers. Be sure to water deeply after any pruning in this oppressive dry heat. (Okay, its humid — I meant “no rain”!)

Counterfeit compost

Josh in Annapolis writes: “This spring I had a landscaping company put down two inches of ‘compost’ in all of my beds. The alleged ‘compost’ is full of wood and plastic debris and is constantly growing thousands of mushrooms. I usually get a product called Leafgro, but my landscaper said that the gardening center he uses no longer carries that product. I’ve worked with this landscaper for many years and he is an honest guy.”

Then he was duped, Josh. Leafgro — an excellent yard waste compost made by the state of Maryland — is abundant (and, as you later discovered, was available at that gardening center all along). But the suspicious side of me (that would be my left and right side) suspects that a quality product like Leafgro might be a tad more expensive than what you got — which was half-composted wood chips (or maybe chipped-up construction debris, pallets and other wood trash).

This diagnosis is certain: You can still see some wood — a sure sign that the material is not yet compost, and those thousands of mushrooms seal the deal.

The Umpire of Horticulture says, ‘Get that outta here!’

Josh in Annapolis continues: “Would you expect legitimate compost to sprout mushrooms? Do you recommend removing this stuff and replacing it with fully composted material?”

Again, legitimate compost would not grow ’shrooms, Josh. That’s the (overwhelming) evidence that you got stuck with half-rotted wood chips (or wood trash).

And yes, I think that your landscaper needs to do the right thing and remove this mess and replace it with the Leafgro you originally intended.

FULL DISCLOSURE: The Espoma Company (maker of Holly Tone) provides national underwriting support for “You Bet Your Garden,” Mike McGrath’s nationally syndicated public radio show. These funds go directly to public radio. McGrath receives none of this funding or any other financial consideration from The Espoma Company (although the company that makes Miracle-Gro did pay him directly to make a personal appearance in the D.C. area in the late ’90s.* Go figure.)

*Yes, he did keep asking, “You know who I am, right?”

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