Growli
Let's go

Plant care

Clethra alnifolia 'Ruby Spice' (Ruby Spice summersweet) care

Clethra alnifolia 'Ruby Spice'

Also called Ruby Spice summersweet, pink summersweet.

RHS H6USDA 4-9Mildly toxic to petsIndoor 1.2-1.8 m tall and 1-1.5 m wide (4-6 ft by 3-5 ft)

Watering rhythm

Bright indirect light (just back from a sunny window)

Keep soil consistently moist; water deeply 1-2 times weekly in the first two seasons and during drought

Jump to schedule→Get smart reminders in the app

Light

Bright indirect light (just back from a sunny window)

Soil

Moist, humus-rich, acidic loam

Humidity

40-70%

Temp

-34 to 32°C

Pet safety

Mildly toxic to pets

Mature size

1.2-1.8 m tall and 1-1.5 m wide (4-6 ft by 3-5 ft)

Care at a glance

Light

Clethra alnifolia 'Ruby Spice' is what florists mean by "bright spot, no direct sun" — close enough to a south or east window to feel the brightness, with a sheer curtain or a few feet of distance keeping the sun off the leaves. Full sun to part shade outdoors; flowers most heavily in sun where soil stays moist, but tolerates dappled woodland shade better than most flowering shrubs. A phone lux-meter at the leaf surface should read 1,500-3,000 lux at noon.

Watering

Water clethra alnifolia 'ruby spice' keep soil consistently moist; water deeply 1-2 times weekly in the first two seasons and during drought. The actual day count varies with pot size, light, and season — the finger test (or lifting the pot to feel its weight) is more reliable than a fixed calendar. Empty any drainage saucer afterwards so the pot isn't sitting in water. A wetland-edge native that resents drying out. Established plants tolerate brief flooding and boggy ground; the main stress is drought, which scorches leaf margins and curtails bloom.

Soil and pot

Clethra alnifolia 'Ruby Spice' grows best in moist, humus-rich, acidic loam. Prefers acidic to neutral soil (pH 5.0-6.5) high in organic matter. Tolerates clay and periodic standing water; dislikes thin, dry, alkaline ground. Mulch to conserve moisture. A pot with a working drainage hole is non-negotiable for this species — even free-draining mix will turn soggy in a closed planter. If you love the look of a decorative pot without a hole, use it as a cachepot around an inner nursery pot you can lift out to water.

Humidity and temperature

Clethra alnifolia 'Ruby Spice' sits happiest at around 40-70% humidity and -34 to 32°C (-29 to 90°F). An outdoor shrub indifferent to ambient humidity; soil moisture matters far more. Performs well in humid coastal and continental climates alike. If you keep the room above year-round and avoid placing the plant near a cold draught, a hot radiator, or an air-conditioning vent, you have already handled the two biggest indoor stressors.

Fertilising

Feed clethra alnifolia 'ruby spice' sparingly. Light feeder. Apply a balanced or acid-forming (rhododendron-type) granular fertiliser once in early spring, or simply top-dress with compost. Avoid high-nitrogen feeds that push leaf at the expense of bloom. Skip fertiliser entirely on a stressed, recently-repotted, or actively wilting plant — fertiliser salts make damage worse, not better. Wait for a round of healthy new growth before resuming a feeding rhythm.

Common problems

Below are the issues we see most often on clethra alnifolia 'ruby spice' in the Growli community. Each is annotated with the most common cause so you know where to start.

  • Leaf scorch from drought — Browning, crisping leaf margins signal the soil dried out — this moisture-loving native is far less drought-tolerant than typical shrubs. Mulch and water deeply.
  • Chlorosis in alkaline soil — Yellowing leaves with green veins indicate the soil is too alkaline, locking out iron. Acidify with elemental sulfur or an acid-forming fertiliser.
  • Sparse bloom in deep shade — Too little light produces leggy growth and few flower spikes. Move to a brighter spot or thin overhead canopy for more sun.
  • Spider mites in hot, dry spells — Stippled, dull foliage and fine webbing appear when plants are heat- and drought-stressed. Rinse foliage and restore even soil moisture.

Propagation

Easiest by softwood or semi-ripe cuttings in early to mid summer under mist, or by digging up and dividing rooted suckers in spring or autumn. Seed is viable but slow and won't reliably reproduce the pink flower colour. Propagation is the cheapest, most satisfying way to expand a collection — and it doubles as insurance against losing a mature plant to an accident. Take a backup cutting once the parent is established and healthy.

Toxicity to pets

Clethra alnifolia 'Ruby Spice' is mildly toxic to pets. Clethra alnifolia is not individually listed on the ASPCA's toxic or non-toxic plant database, so a positive safety listing cannot be confirmed. Treat with caution and verify with a vet; ingestion of plant material may cause mild gastrointestinal upset in pets. If you keep cats, dogs, or curious children in the house, weigh placement carefully — a high shelf or a hanging planter is enough for casual safety. For severe ingestion incidents, call your local vet and the ASPCA Animal Poison Control Center (in the US, 888-426-4435).

Pet-safety status is sourced from the ASPCA Toxic and Non-Toxic Plant List, which catalogues the most-asked-about plants for cats, dogs, and horses.

Clethra alnifolia 'Ruby Spice' care — frequently asked questions

What is the common name for Clethra alnifolia 'Ruby Spice'?

Clethra alnifolia 'Ruby Spice' is most commonly called Clethra alnifolia 'Ruby Spice', but it is also known as Ruby Spice summersweet, pink summersweet. The names refer to the same species, so care instructions for Clethra alnifolia 'Ruby Spice' apply identically to anything sold as Ruby Spice summersweet.

How much light does clethra alnifolia 'ruby spice' need?

Clethra alnifolia 'Ruby Spice' grows best in bright indirect light (just back from a sunny window). Full sun to part shade outdoors; flowers most heavily in sun where soil stays moist, but tolerates dappled woodland shade better than most flowering shrubs.

How often should I water clethra alnifolia 'ruby spice'?

Water clethra alnifolia 'ruby spice' keep soil consistently moist; water deeply 1-2 times weekly in the first two seasons and during drought. A wetland-edge native that resents drying out. Established plants tolerate brief flooding and boggy ground; the main stress is drought, which scorches leaf margins and curtails bloom. The finger-test (or lifting the pot to feel its weight) beats a fixed weekly calendar because pot size, light, and season all change how fast the soil dries.

Is clethra alnifolia 'ruby spice' toxic to cats and dogs?

Clethra alnifolia 'Ruby Spice' is mildly toxic to pets. Clethra alnifolia is not individually listed on the ASPCA's toxic or non-toxic plant database, so a positive safety listing cannot be confirmed. Treat with caution and verify with a vet; ingestion of plant material may cause mild gastrointestinal upset in pets.

What USDA hardiness zone does clethra alnifolia 'ruby spice' grow in?

Clethra alnifolia 'Ruby Spice' is rated for USDA zone 4-9 and RHS hardiness H6. Outside that range, grow it as a container plant that overwinters indoors before the first hard frost.

Clethra alnifolia 'Ruby Spice' deep-dive guides

Every aspect of clethra alnifolia 'ruby spice' care, each with its own calibrated guide:

Featured in these plant shortlists

Clethra alnifolia 'Ruby Spice' qualifies for 5 curated Growli shortlists — each one filtered objectively from our structured plant-care library, so the selection is consistent and checkable:

Related guides

Clethra alnifolia 'Ruby Spice' is also commonly called Ruby Spice summersweet or pink summersweet.