Is it deer resistant?

Yes

Balloon Plant is deer resistant.

Gomphocarpus physocarpus

Deer: Rarely
Height: 6 ft (1.8 m)
Spread: 3 ft (91 cm)
Zones: 8–11
Light: Full sun

Perennial

Balloon Plant (Gomphocarpus physocarpus)

Photo: Daderot · CC0

Also called American Silkweed, Jewelweed, Milkweed, Silken Cissy

Perennial Gomphocarpus

More details

Light: Full sun
Water: Low, Medium
Type: Perennial
Maintenance: Low
Features: Drought tolerant

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Balloon Cotton-Bush
Gomphocarpus physocarpa