Leaf Drop, Rain, and the Six-Week Window: Getting Every Zone Ready for What's Next

By Michael White, ISA Certified Arborist (KY-0847A) and Kentucky Master Gardener

September 17, 2026 — Union/Florence, KY (Zone 6b): Overnight lows here are sliding into the mid-50s by early next week — 54° by Saturday the 20th — and we're sitting roughly four to six weeks out from our average first frost. My adeniums are reading that shift before I am. Leaf drop is already underway on several of my older caudex specimens. Rain is scattered through the whole seven-day window, nothing dramatic, but the pattern's changing: cooler nights mean slower drying between waterings, and that's exactly the condition that turns a mediocre potting mix into a rot problem.
That's the theme of this one. No matter which region you're growing in, something is shifting right now. It's not the same shift everywhere, and it's not on the same calendar — but every one of you needs to be doing something different than you were doing three weeks ago. Let's walk through it.

Why Leaf Drop Is Happening Right Now
I get asked this every September, and the short answer is: your plant isn't sick, it's paying attention. Leaf drop in Adenium, and to a lesser degree Plumeria, isn't triggered by cold alone. It's triggered by shortening day length combined with a drop in overnight temperature. The plant reads both signals and starts pulling resources out of the leaves and back into the caudex, which is exactly what you want it to do heading into dormancy. A caudex that's storing energy well going into winter is a caudex that comes back strong in April.

Where growers get into trouble is panicking over leaf drop like it's a problem to fix. In most cases, especially once you're past the first week or two of yellowing and thinning, it's not a fix-it situation — it's a get-ready-for-what's-next situation.

The Rain Problem Nobody Talks About
Here's the part that catches people off guard. As we move into fall, most of us — outside of the Gulf Coast, which never really leaves its rainy pattern — start seeing more rain show up in the forecast, and it comes at exactly the moment root activity is slowing down. That's a bad combination if your media isn't built for it.

When a plant is actively growing in July, it's pulling moisture out of the pot fast enough that a slower-draining mix doesn't have time to sit wet around the caudex. In September and October, with growth slowing and days shortening, that same mix can stay damp for days. That damp period sitting right at the base of the caudex is where rot starts. I've lost plants to this exact scenario more than once over the years, and every time, the culprit was moisture sitting where it shouldn't.

This is exactly why I engineered Desert Oasis Potting Media the way I did. It's not just "well-draining" in the generic sense every bag on the shelf claims to be — it's built specifically so water moves away from the caudex quickly instead of wicking back up and sitting against it. That distinction matters more in October than it does in July, and it matters more in Zone 6 and 7 than it does in Zone 9, but it matters everywhere rain is picking up while root activity is winding down.

Mature Plants Are Closing Out — Which Means It's Seed-Starting Season

For a lot of you, this is also the point in the year where your mature plants are done producing new growth for the season. That's not a loss — that's a cue. The window that's closing for mature plants outdoors is the same window that's opening for starting seed indoors under lights, and starting now gives you a five-to-six-month head start on next spring instead of trying to catch up in April.

I'll be honest about my own situation here, because it's relevant. I've got a limited amount of indoor overwintering space, and every mature caudex I bring in this fall takes up room I'd rather be using for germination trays. I brought in a substantial amount of seed stock back in June and July of this year, and I'd genuinely rather see that seed in your growing setup, sprouting under your lights, than sitting in inventory taking up space I need for my own overwintering plants. That's not a marketing line — that's exactly the tradeoff I'm making in my own greenhouse right now.

If you've been thinking about starting Adenium, Plumeria, or Pachypodium from seed, this is the window. A seedling started this month is a plant with real root development and caudex structure by the time everyone else is starting from scratch next April.

The full regional breakdown — with specific timing and application guidance for Cold Climate, Pacific Northwest, Gulf Coast, and Western growers — is at americanadenium.com.

What We're Growing With
Desert Oasis Potting Media — engineered specifically so moisture moves away from the caudex instead of sitting against it, which is exactly what matters as rain increases and root activity slows down heading into fall.
Shop Desert Oasis Media →

Adenium, Plumeria, and Pachypodium Seeds — this summer's seed stock, ready to start now for real head start on 2027. I brought in more than I have room to sow myself this year, and I'd rather see it germinating for you than sitting in my inventory through winter.
Shop Seeds →

Cheers,

Michael