PACIFIC NORTHWEST (Zones 7b–9)

Most growers pick one arabicum line and sow it. You learn what that line does. You don't learn what makes it different from anything else.

For Pacific Northwest growers there's a second problem stacked on top of that one. Your limiting factor isn't cold — most of you sit in 8a through 9 and won't see a hard freeze that threatens a properly housed plant. Your limiting factor is heat units and light. Adenium arabicum builds caudex mass on accumulated warmth, and the marine climate simply doesn't deliver much of it. That constraint changes which cultivars reward you and how you have to grow them.

Which makes a controlled comparison unusually valuable here. Same tray, same media, same light, same water. The only variable is genetics — and you find out which of these lines actually performs under your conditions rather than under Thailand's.

The five, and what separates them

God Songkla carries genetics out of the Southern Thai networks around Songkhla province. Its signature is a symmetrical dome crown that forms with almost no corrective wiring — primary branches emerge closely spaced into a unified umbrella. Bark matures clean silvery-gray to light bronze rather than dark, so the plant reads on structure rather than skin tone. Short internodes stack foliage tight at the branch tips.

Be aware that tight internode spacing is a light-dependent trait, not just a genetic one. Under PNW light without supplementation, this is the line most likely to stretch and lose the dome symmetry that makes it worth growing.

Black Monk is the vertical outlier among dark-skin arabicum. Where Black God, Black Hole and Kalamae all spread low and wide, Black Monk throws tall, heavy, uniform branches straight up from a muscular base, reaching around two feet in a container. Because there's no horizontal skirt over the base, the caudex stays fully exposed and the dark bark becomes the subject of the plant.

Set your expectations correctly on this one. That near-black bark is a UV-triggered melanin response. In a coastal marine climate with persistent cloud cover, it will not lock in on ambient light — you'll get a dull smoky green instead. High-output full-spectrum lighting isn't optional for this cultivar in your region; it's the difference between the plant you ordered and a disappointment.

D2 × Boar pairs two competition lines. D2 forces extreme horizontal expansion — pancake geometry, ultra-short internodes, plate-like lateral roots. Boar brings rugged textured silver-gray bark and a dense, rigid crown of thick vertical primaries. Together: a flat swollen base under a dense umbrella. Being a cross, expect a spectrum, with some seedlings leaning toward compression and others toward bark and branching vigor.

This is the cross that most rewards a greenhouse in your climate. The pancake compression that makes it valuable is heat-driven.

Riza is bred for structure over color and builds something none of the others do — multiple thick trunk bases fusing into one broad, low foot, giving genuine multi-trunk character without grafting. Branching emerges radially from the caudex top in clean, even spacing.

It's also the strongest root-training candidate in the set, genetically inclined toward dense symmetrical radial root networks. And it takes water differently from the rest: unlike the dark-skin lines that want a dry cycle, Riza rewards aggressive watering during peak growth. In a wet climate that's an unusual advantage — this is the one line here whose preferences run with your weather rather than against it.

Tyson goes wide and heavy. The caudex expands laterally into a thick, low shield base with deep wrinkles and blocky ripples. Primary stems come out with real girth at the caudex shoulders and stay stubby, with hyper-short internodes. Bark matures to a silvery-gray and charcoal-bronze metallic sheen that tightens under sun stress and strict dry cycles.

The metallic finish needs those dry cycles. In a region where ambient humidity works against you, that means controlling water rather than letting the climate dictate it.

Why these five together

The set covers two horizontal builders (D2 × Boar, Tyson), one vertical (Black Monk), one symmetrical dome (God Songkla), and one multi-trunk (Riza). Three bark strategies. Two opposing watering regimes running side by side where you can observe the difference directly.

For a low-heat grower there's a further payoff. Running all five under identical conditions tells you which lines tolerate your heat deficit and which ones need a greenhouse before they're worth your money. That's information you cannot get from growing one cultivar.

Individually those five packs run $62. The set is $49.

Heat is the constraint, so you supply it

Arabicum germinates at 85–95°F. That number doesn't care what your ambient temperature is, and in the Pacific Northwest in September you're not getting there without help — not on a windowsill, not in a warm room.

Bottom heat and a humidity dome are what close the gap between a tray that germinates in the 90% range and a tray that sits cold and rots. I run the Luxbird Professional Seed Germinator & Propagation Kit for this, and in a climate with a structural heat deficit it does more work for you than it does for me. Every degree you're not getting from the environment has to come from equipment.

Coastal Oregon and Washington growers (8b–9): Mild winters, but the lowest heat unit accumulation of anyone reading this and persistent marine cloud cover. Plan on supplemental heat and high-output lighting as permanent infrastructure, not a seasonal assist. Black Monk's dark bark and God Songkla's tight internodes are both at risk here without it. If you're only going to invest in conditions for part of the set, prioritize those two.

Willamette and Puget lowland growers (8a): You get meaningfully more summer heat than the coast, but a short season to use it in. A greenhouse or polytunnel changes the math substantially — it extends your usable window on both ends and lets D2 × Boar express the pancake compression it's bred for. Without one, expect slower caudex development than the descriptions suggest and judge these lines on a three-year horizon rather than one.

Inland and higher elevation growers (7b): You have more heat units than the west side and genuinely cold winters, which puts you closer to a cold-climate protocol than a coastal one. Sow indoors now under heat, run under lights through winter, and treat your outdoor season as the real growing window rather than a supplement. Your heat advantage is real — use it, and bring everything in well before your first hard freeze.

What We're Growing With

Desert Oasis Potting Media — 2.75 dry quarts of ready-to-use inorganic mix. Matters more in a wet climate than a dry one.

5×5 Germination Tray — sized for clean single-variety sowing so a five-way trial doesn't get crossed up.

Adenium arabicum Form Study Set — five seeds each of God Songkla, Black Monk, D2 × Boar, Riza and Tyson. Twenty-five seeds, individually labeled by variety. $49.

Adenium Seed reference — cultivar background and germination protocols.

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

— Michael White, ISA Certified Arborist KY-0847A, Kentucky Master Gardener