Ipomoea nil

Plant Profile & Key Characteristics

Overview: A fast-growing herbaceous twining vine of 2-5 m (6-15 ft), grown as an ornamental annual (or tender perennial) for its blue-purple morning flowers. Vigorous and self-seeding.

Quick Specifications

Specification	Attribute
Plant Type / Life Cycle	Perennial (evergreen) grown as an annual; annual in cold climates
Foliage Type	Evergreen where frost-free; herbaceous annual elsewhere
Mature Size	2-5 m (6-15 ft) climbing
Growth Rate	Fast
Root System	Fibrous
Toxicity	Seeds toxic if ingested (contain alkaloids)
Hardiness	USDA zone 10+ as perennial; zone 6+ grown as an annual

Growth Form & Structure

• Height & Spread: Twines 2-5 m (6-15 ft) up a support in the ground; in a container (10-30 L / 2.5-8 gal) it stays smaller and needs a trellis.
• Growth Habit & Form: Fast, twining annual/perennial vine; can be aggressive and self-seeding.
• Lifespan & Maturity: Reaches flowering size in a single season.

Anatomy & Physical Features

• Leaves & Foliage: Green, heart-shaped (to deltoid) leaves.
• Flower Characteristics: Round, funnel-shaped blue-purple flowers, sometimes with a pinkish hue, opening in the morning (see the Bloom guide).

Primary Uses & Landscape Value

• Functional & Ornamental Roles: Ornamental climber for trellises, fences and pergolas; also used as a fast groundcover or informal screen. Grows in large containers.

Care Guide: Planting, Soil & Watering

Overview: A vigorous herbaceous vine that thrives in full sun to part shade in warm, frost-free conditions. It grows best in rich, moist, well-ventilated soil with good drainage and appreciates steady moisture through the growing season.

Quick Care Requirements

Requirement	Ideal Condition
Planting Season	Spring after last frost (as annual); year-round in zone 12+
Growth Rate	Fast
Soil Type	Rich, moist, well-ventilated soil with good drainage
Water Need	Moderate to High – keep the soil evenly moist

Planting & Establishment

• Best Planting Season: Plant in spring after the last frost as an annual; where hardy, spring in zone 10a, spring to summer in 10b, spring to autumn in 11, and year-round in zone 12+.
• How to Plant:
  • Hole Preparation: Dig the hole about 50% wider than the root ball so the roots can spread into loosened soil.
  • Soil Amendments: Mix the excavated soil with organic matter, humus and dead leaves before backfilling to enrich and lighten it.
  • Planting Depth: Set the plant so the root collar sits level with the surrounding soil; firm gently but firmly so it will not topple, and install a trellis or support at planting time.
• Growth Speed & Expectations: In optimal conditions this is a fast grower that can cover a support in a single warm season.

Soil, Watering & Drainage Care

• Soil Mix & Drainage Needs: Rich, moist but well-ventilated soil with good drainage; in containers (10–30 L) use free-draining mix with ample holes and avoid a permanently full saucer.
• Watering Schedule & Technique:
  • Young / Newly Planted: Water twice on the first day of planting, then daily for the first two weeks while the roots establish.
  • Established: Once established, water regularly to keep the soil evenly moist; morning glories dislike drying out completely. It appreciates generous moisture but dislikes waterlogging.
  • Seasonal Adjustments: Give more water in summer heat and taper off in cooler weather or winter dormancy.

Climate, Light & Hardiness

Japanese morning glory is a fast tropical and subtropical vine, grown as a tender perennial in frost-free climates and as a warm-season annual elsewhere, flowering in full sun to half shade. It thrives in warmth and humidity but has essentially no frost tolerance, so cold is the factor that forces annual treatment outside roughly USDA zone 10.

Quick Climate Specifications

Climate Zones	Tropical, Mediterranean, desert, subtropical, temperate
USDA Hardiness Zones	About 10+ as a perennial; about 6+ grown as a warm-season annual
Optimal Temp Range	Approximately 22–30 °C (72–86 °F)
Cold Damage Begins	At or near freezing
Approx. Survival Minimum	Foliage killed by frost; perennial only where winters stay essentially frost-free (about zone 10+)
Frost Tolerance	None to Very Low
Light Conditions	Full sun to half shade
Wind Tolerance	Moderate (twining stems need support)

Sunlight & Light Exposure

Optimal Light Setup

Full sun for the most flowers; it tolerates half shade with reduced bloom.

Direct Sun Requirement

At its best in full, direct sun.

Best Exposure / Orientation

A warm, sunny wall, fence or trellis maximises flowering.

Temperature Extremes & Hardiness

USDA Hardiness & Regional Limits

Perennial in frost-free zones (about 10+); in zones 6–9 it is grown as a warm-season annual and killed each winter, so cold limits year-round outdoor culture rather than the plant being merely an annual.

Cold Damage & Winter Protection

Frost kills top growth; plants can be overwintered indoors and set back out after the last frost.

Frost Sensitivity

High.

Extreme Heat Tolerance

Good; a warm-climate vine, though the hottest days are avoided for sowing.

Frost-Free Growing Season

It needs a warm, frost-free stretch to flower well, and germinates best in warm soil around 22–30 °C (72–86 °F).

Wind, Humidity & Microclimate

Humidity Preferences

Enjoys warm, humid air.

Wind Tolerance

Soft twining stems need support; sheltered spots protect the delicate flowers.

Microclimate Recommendations

A warm, sheltered, sunny microclimate maximises flowering and season length.

Growing in Pots, Balconies & Indoors

Ipomoea nil is a fast morning-glory climber reaching 2-5 m, and it flowers well from a good-sized pot given something to climb. It is not a houseplant – it needs full outdoor sun and room to scramble – so grow it on a sunny balcony or patio with a trellis, railing or strings for support.

Quick Details

• Container Size: 10-30 L (2.5-8 gal) – bigger is better for a fast climber
• Indoor Suitability: Not indoors – a vigorous climber needing full outdoor light
• Best Spot: Full sun to part shade (more sun means more flowers), with support
• Soil & Drainage: Well-ventilated, free-draining mix rich in organic matter
• Watering in Pots: Keep evenly moist – average to generous water; a pot dries fast

Indoors & On the Windowsill

• Houseplant limits: The grower marks it as not an indoor plant – it climbs fast, needs full sun to flower, and soon outgrows any room.
• Windowsill growing: Not suitable as a sill plant; grow it outdoors with support.
• Safety: Morning-glory seeds are toxic if eaten – keep seed packets and plants away from children and pets.

On a Balcony or Patio

• Light, support & wind: A sunny balcony or patio is where this climber shines – give it a trellis, railing or strings to climb and shelter it from strong wind, which shreds the soft growth. Reflected heat from walls dries the pot fast, so check moisture daily in warm weather. A drip irrigation kit with a timer can take over that watering check automatically.
• Practicalities: Make sure the filled pot and its support are stable and that drainage runoff can escape freely without pooling below.

Choosing the Pot, Soil & Long-Term Care

• Pot & drainage: Use a container of 10-30 L (2.5-8 gal) – bigger is better for these fast, hungry climbers. Keep the soil moist and make sure water drains out; it is better not to use a saucer under the pot.
• Potting mix: A well-ventilated mix with good drainage, rich in organic matter – a general potting mix, or peat soil with perlite or vermiculite.
• Feeding: Feed through the growing season; nutrients leach from pots faster than from open ground.
• Repotting (as a perennial): Every two years, switch the soil and prune back part of the roots and the top growth to keep it healthy.

Fertilizing & Feeding

Morning glory is an ornamental flowering vine fed mainly in spring; it wants balanced nutrition and rich, moist soil, but excess nitrogen gives rampant vine and fewer flowers.

Quick Fertilizing Specs

Feeding Level	Moderate
Main Nutrient Priority	Balanced nutrition; keep nitrogen in check for better bloom.
Best Feeding Period	Mainly in spring as growth begins, easing through summer.
Organic Options	Compost, humus and organic matter mixed into the soil.
Micronutrients	Usually covered by a complete fertilizer and rich soil; correct iron only if new growth yellows.
Soil pH	Tolerates a wide range; near neutral, rich, moist, well-drained soil is ideal.
Reduce/Stop Feeding	Ease off feeding after the flush of growth and through winter rest.

Feeding by Growth Stage

Spring growth flush

Support fresh shoots and leaves as the plant wakes up in spring.

Nutrient direction	A balanced complete feed with adequate nitrogen fuels healthy new growth.
Timing	As new growth begins in spring.
Frequency	A light, regular feed as spring growth begins.
Fertilizer types	A balanced complete fertilizer, Compost or well-rotted organic matter
Precautions	Keep feeding moderate; overly rich soil softens growth. Avoid heavy nitrogen, which drives leaves at the expense of flowers.

Flowering

Sustain flowering without pushing excess foliage.

Nutrient direction	A balanced feed supports steady bloom; adequate nitrogen, not high phosphorus, drives flowering.
Timing	Through the flowering season.
Frequency	Light, regular feeding through the flowering period.
Fertilizer types	A balanced complete fertilizer
Precautions	High-phosphorus ‘bloom booster’ feeds are unnecessary; a balanced feed and full sun give better flowering. Avoid heavy nitrogen, which drives leaves at the expense of flowers.

Dormancy or winter rest

Let the plant rest through cold or dormant months without forcing growth.

Nutrient direction	None – withhold fertilizer while the plant is not actively growing
Timing	During dormancy or cool-season rest when growth has stopped
Frequency	No feeding at this stage
Fertilizer types	No feeding at this stage – resume only when active growth returns
Precautions	Do not fertilize until active growth resumes; feeding a resting plant risks salt buildup and root injury

Nutrient Deficiency Signs & Corrections

Older, lower leaves fade to pale green or yellow overall and growth slows.

Possible causes	Low soil nitrogen or thin organic matter, Nitrogen leached out by heavy watering or rain on light soils, Cold, waterlogged roots limiting uptake
Appears first on	older, lower leaves
What to check	soil organic matter and recent feeding, whether heavy rain or irrigation may have leached nutrients, overall plant vigor and colour
Possible correction	Topdress with compost or apply a balanced complete fertilizer at label strength; keep watering steady but not excessive so nutrients are not washed away.

Youngest leaves yellow between the veins while the veins stay green.

Possible causes	High or alkaline soil pH locking up iron, Cold or waterlogged soil slowing root uptake, Genuinely low available iron
Appears first on	newest leaves at the shoot tips
What to check	soil pH and drainage, whether the soil is cold or saturated, overall root health
Possible correction	Correct soil pH and improve drainage first; if the youngest growth stays chlorotic, apply a chelated iron product following its label.

Lush leafy growth but few flowers.

Possible causes	Too much nitrogen from over-feeding, Overly rich soil relative to light levels, Insufficient sunlight for the demand created by heavy feeding
Appears first on	new leafy shoots at the expense of buds
What to check	recent feeding rate and fertilizer type, light exposure, balance of leaf growth versus budding
Possible correction	Ease back on nitrogen and switch to a balanced feed; ensure full sun so the plant channels energy into flowering rather than foliage.

Pruning, Training & Seasonal Maintenance

Ipomoea nil is a soft, herbaceous twining vine that tolerates cutting well but rarely needs it for the plant’s own sake. Where it’s grown as an annual (most temperate gardens), it completes its life cycle and is removed at season’s end without any real pruning. Where it persists as a tender perennial (hardiness zone 10a and warmer), an early-winter or post-bloom cutback tidies the vine and clears the way for fresh growth next season; cutting hard during the main flowering flush simply removes the current display for no benefit.

Quick Pruning & Maintenance Specs

Pruning Tolerance	High (herbaceous), but largely optional
Primary Pruning Window	After the bloom flush or in early winter (perennial-grown plants only)
Secondary Maintenance Window	Ongoing spot-trims through the season for shape/borders
Typical Frequency	Occasional; none needed for annual-grown plants
Main Objective	Define borders, keep growth within bounds, remove dead material
Young Plant Priority	Get the leading shoot onto a support quickly
Mature Plant Priority	Contain the vine’s spread; it self-describes as aggressive/invasive in the growing record
Best Tool Type	Precision snips for soft twining stems
Avoid Heavy Pruning During	Peak bloom

Pruning by Plant Age & Size

Newly Established

Minimal: remove only damaged growth and get the seedling onto a support promptly, since it climbs by twining and needs something to grip early.

Young / Formative

Staking/trellis training only – there is no formal branching framework to build, just guide the leading shoots as they extend.

Mature / Established

For perennial-grown plants in warm zones: general containment pruning to stop the vine overrunning its space, and periodic removal of old tangled growth to make room for fresh flowering shoots.

Seasonal Pruning Schedule

Post-Flowering (perennial-grown only)

Objective: tidy the vine and encourage fresh growth. Remove: spent flowering stems and old tangled growth. Do not remove: any stem still actively flowering. Expected response: renewed flush of twining growth the following season. Flowering impact: none negative – this timing is chosen specifically to avoid cutting off active bloom.

Ongoing Sanitary

Remove dead or frost-collapsed material at any time; annual-grown plants need no seasonal schedule beyond this.

Structural Pruning & Training

Guide the twining stems onto a support, and periodically rein in growth reaching beyond its allotted space – the plant’s own growing notes flag it as aggressive/invasive, so containment is a genuine, recurring task rather than a cosmetic one.

Special Growth to Remove

• Dead or frost-collapsed stems
• Excess vine reaching beyond its support or into neighbouring plants

Container & Small-Space Pruning

Grows well in pots given a support; pinch more often than an in-ground plant to keep it compact, since a container restricts the root run that would otherwise fuel unchecked spread.

Tools

• Precision snips – for all shaping and deadheading; stems stay soft and thin
• Soft ties/stakes – for training onto a trellis while establishing

Tool Hygiene & Disease Risk

Routine: clean, sharp tools are enough. Recorded pests (weevil, moth, whitefly, aphids) are not typically spread by pruning cuts.

Cut Placement & Technique

Cut or pinch just above a node; guide twining tips onto the support rather than forcing them into position.

Heavy Pruning & Rejuvenation

For perennial-grown specimens, a hard early-winter cutback is tolerated well and renews the plant for the next season. This doesn’t apply to annual-grown plants, which simply complete their life cycle and are removed.

Post-Pruning Care

After a post-bloom cutback, resume normal watering; no special feeding is needed.

Common Pruning Mistakes

• Leaving the young vine untrained so it tangles into a dense mat that’s hard to selectively prune later
• Cutting back hard mid-bloom and losing the current flower display for no horticultural benefit

When NOT to Prune

Avoid major cutback during peak flowering. For plants grown as annuals, no pruning is needed at all beyond removing dead material.

Recommended Tools (by task)

• Shaping/deadheading soft stems – precision_snips: the vine never develops woody tissue
• Training onto a trellis – soft_ties_stakes: guides growth while the twining habit establishes

Propagation Guide

Japanese morning glory is easy both ways: it grows readily from its hard-coated seed and roots just as easily from stem cuttings, which the site notes are the simpler start and also allow layering. Cuttings reproduce a plant exactly, while seed of the species is fairly uniform; overall an Easy vine.

Quick Propagation Specs

Best Propagation Method	Stem cuttings
Alternative Methods	Seed (species and mixes) — and cuttings
Propagation Difficulty	Easy
Seed True-to-Type	Mostly uniform for the species; named Japanese colour strains can segregate — keep those by cuttings
Vegetative True-to-Type	Yes — a cutting or layer reproduces the parent, including flower colour
Best Propagation Season	Spring to summer
Seed Germination Time	2–7 weeks
Cutting Rooting Time	A few weeks under warm, humid conditions
Germination Temperature	22–30°C (72–86°F)
Seed Sowing Depth	1 cm (0.5 in)

Growing from Seed

Seed Handling & Viability

Store seed in a dark, dry place until sowing.

Dormancy & Pre-Sowing Treatment

Morning glory seed has a hard coat; nicking it or soaking it in water overnight before sowing softens the coat and gives quicker, more even germination.

Sowing Season, Depth & Spacing

Sow in spring in most zones (and, in the warmest zones, from spring through autumn or year-round, avoiding the hottest days of summer). Sow about 1 cm (0.5 in) deep, spacing about 30×40 cm (12×16 in), or 4×4 cm (1.8×1.8 in) if pricking out seedlings to transplant. Sowing into peat with vermiculite — or adding vermiculite around the seed — helps hold moisture.

Germination Conditions & Time

Germinate at about 22–30°C (72–86°F) in moist soil with high humidity, ideally in a sunny spot. Emergence is spread over roughly 2–7 weeks, so germination can be staggered; soaking beforehand shortens the wait.

Seedling Care

Water seedlings regularly and never let them dry out.

Stem Cuttings

Best Timing

Take cuttings from spring to summer, when the vine is in active growth.

Rooting Setup

Root either in water — changing it every few days — or in moist soil kept constantly damp, keeping the cutting warm, around 25–30°C (77–86°F), with high humidity.

Rooting Hormone

Optional — the soft stems root readily on their own, though a rooting hormone can help.

Air & Ground Layering

Because these vines root easily along their stems, a length of stem can be bent down, covered with moist soil and left to root, then separated from the parent — a simple way to gain an extra plant identical to it.

Bloom & Flower Guide

Quick Details

• Bloom Season: Spring, summer and autumn
• Time to First Bloom: Within the first season for plants grown as annuals
• Flower Appearance: Round, funnel-shaped flowers in blue and purple, sometimes with a pinkish flush
• Edibility: Not eaten – an ornamental vine; the seeds in particular are toxic

Detailed Blooming Overview

Japanese morning glory is grown for its beautiful funnel flowers, which open fresh each morning and fade by afternoon. A well-grown vine produces a long succession of blooms, giving a new display day after day.

Flower Characteristics

• Round, funnel-shaped flowers in blue to purple, sometimes with a pink tint.
• Each flower lasts a single morning; new buds open the next day.

Bloom Care & Thinning

• Managing the bloom: Full sun, a support to climb and lean soil encourage flowers over leaf; too much nitrogen delays blooming.
• Pollination: Visited by bees and other insects in the cool of the morning.

Bloom Health & Protection

• Safety: Morning glory seeds are toxic if eaten – enjoy the flowers as an ornamental and keep seeds away from children and pets.

Pests, Diseases & Troubleshooting

Overview: Ornamental morning glories are fast, tough climbers that are rarely troubled seriously; their common visitors are chewing tortoise beetles and caterpillars plus sap-sucking aphids and whitefly, with rust and leaf spot the main diseases. Most ‘problems’ are really vigor — they self-seed and can become weedy — and poor flowering from excess nitrogen.

Quick Troubleshooting Overview

Issue / Pest	Main Symptom	Primary Solution
Tortoise / flea beetles	Small round holes and pits in leaves	Tolerate light damage, hand-pick, neem if heavy
Caterpillars (leaf-rollers, hornworm)	Chewed, rolled, skeletonized leaves	Hand-pick, Bacillus thuringiensis
Aphids	Sticky curled new growth, sooty mold	Water jet, insecticidal soap
Whitefly	Clouds of white flies, honeydew, yellowing	Yellow sticky traps, soap/oil
Spider mites	Stippling and webbing in hot dry spells	Hose foliage, oil/soap
Rust / leaf spot	White or brown pustules/spots on leaves	Airflow, dry foliage, remove leaves

Common Pests & Management

• Tortoise beetles & flea beetles (Charidotella / Cassidinae, Chaetocnema spp.):
  • Symptoms: Golden or metallic tortoise beetles and tiny flea beetles chew small round holes and pits in the leaves; the classic ‘shot-hole’ look, mostly cosmetic on vigorous vines.
  • Prevention & Control: Tolerate light feeding, hand-pick beetles, keep plants vigorous, and use neem or spinosad only if damage becomes heavy on young plants.
• Caterpillars (Sweet potato hornworm, leaf-rollers & webworms (Agrius, Spoladea, Bedellia)):
  • Symptoms: Chewed, skeletonized, or rolled and webbed leaves and defoliated shoot tips from various moth larvae.
  • Prevention & Control: Hand-pick and unroll leaves to remove larvae, encourage parasitic wasps and birds, and spray Bacillus thuringiensis (Bt) for significant infestations.
• Aphids (Aphis / Myzus spp.):
  • Symptoms: Soft green or dark insects on shoot tips and leaf undersides causing sticky, curled, distorted growth and sooty mold; they can spread viruses.
  • Prevention & Control: Blast with water, support ladybirds and lacewings, and use insecticidal soap or neem on stubborn colonies in the evening.
• Whitefly (Bemisia tabaci / Trialeurodes):
  • Symptoms: Clouds of tiny white flies that lift off when disturbed, with honeydew, sooty mold, and yellowing; important virus vectors in warm climates.
  • Prevention & Control: Hang yellow sticky traps, encourage natural enemies, and spray undersides with insecticidal soap or horticultural oil, repeating to break the cycle.
• Spider mites (Tetranychus urticae):
  • Symptoms: Fine stippling, bronzing, and webbing under leaves in hot, dry, stressed conditions.
  • Prevention & Control: Hose foliage, keep plants watered and unstressed, and treat undersides with insecticidal soap or a light horticultural oil.

Diseases & Fungal Issues

• White rust / rust (Albugo ipomoeae-panduratae, Coleosporium):
  • Symptoms: Raised white blister-like pustules or orange-brown rust spots on leaf undersides with yellowing above, in humid conditions.
  • Treatment & Management: Remove and destroy affected leaves, space and train for airflow, avoid overhead watering, and use a labelled fungicide only under heavy pressure.
• Fungal leaf spot & anthracnose (Cercospora, Colletotrichum):
  • Symptoms: Brown, tan, or black spots and blotches on leaves, sometimes coalescing and causing early leaf drop in wet weather.
  • Treatment & Management: Clear fallen litter, improve airflow, keep foliage dry, and apply copper only if spotting becomes severe.
• Stem & root rot / wilt (Fusarium, Rhizoctonia, Pythium):
  • Symptoms: Wilting, yellowing, and a soft rotted stem base or roots in overwet, poorly drained soil.
  • Treatment & Management: Grow in well-drained soil, avoid overwatering, and remove affected plants; give good drainage in containers.
• Viral mosaic (aphid/whitefly-borne):
  • Symptoms: Mottled, mosaic, or distorted foliage and reduced vigor spread by sap-sucking vectors.
  • Treatment & Management: There is no cure — remove symptomatic plants, control aphids and whitefly, and manage weed hosts.

Growing Difficulties & Abiotic Problems

• Aggressive, weedy self-seeding:
  • Cause & Symptoms: The main real ‘problem’: vigorous growth and prolific self-seeding let morning glories climb over and smother neighbors and reappear as volunteers for years.
  • Correction Strategy: Site where vigor is welcome, deadhead before seeds ripen to limit self-sowing, and pull volunteers early; grow on a strong support with room to run. I. nil (Japanese morning glory) self-seeds heavily.
• Poor flowering from excess nitrogen:
  • Cause & Symptoms: Lush leafy vines with few flowers when soil is too rich or over-fed.
  • Correction Strategy: Grow in lean-to-average soil in full sun, avoid nitrogen-rich feeding, and give plenty of light to shift the plant from leaf to bloom.
• Frost sensitivity:
  • Cause & Symptoms: Blackening and collapse of these tender annual/tropical vines at first frost.
  • Correction Strategy: Grow as a warm-season annual in cold climates; sow after frost and expect it to die back with the first hard freeze.
• Hard-coated seed & poor germination:
  • Cause & Symptoms: Slow, erratic germination from the tough, water-resistant seed coat.
  • Correction Strategy: Nick (scarify) and soak seeds before sowing to speed and even out germination.

What Helps — Products & Tools

Ornamental morning glories seldom need much beyond gentle tools: a water jet, insecticidal soap, and neem for aphids, whitefly, and mites, Bacillus thuringiensis for caterpillars, and yellow sticky traps for whitefly. Airflow and sanitation handle rust and leaf spot; copper is a last resort. The main ‘management tool’ is restraint — deadheading and pulling volunteers to curb their weedy vigor.

Frequently Asked Questions

How do you grow Ipomoea nil (Japanese morning glory) from seed?

Nick or soak the hard-coated seed overnight before sowing to speed and even out germination, then sow it about 1 cm (0.5 in) deep in warm, moist soil around 22–30°C (72–86°F). Germination is spread over roughly 2–7 weeks, so expect staggered emergence, and water seedlings regularly, never letting them dry out.

How do you grow Japanese morning glory?

Give it full sun for the most flowers (it tolerates half shade with reduced bloom) and a sturdy support to twine up, since it can twine 2-5 m (6-15 ft). It grows best in rich, moist, well-ventilated soil with good drainage and appreciates steady moisture through the growing season, and heavy nitrogen feeding should be avoided since it drives leaves at the expense of flowers.

Is Japanese morning glory toxic?

Yes – the flowers are grown purely as an ornamental and are not eaten, and the seeds contain alkaloids and are toxic if ingested, so keep seed packets and plants away from children and pets.

Does Japanese morning glory come back every year, or is it an annual?

It’s only a perennial where winters stay essentially frost-free, roughly USDA zone 10 and warmer. In zones 6-9 it is grown as a warm-season annual and is killed each winter, so it needs resowing the following spring.

Is Japanese morning glory invasive or does it spread aggressively?

Yes – it self-seeds heavily, and vigorous growth and prolific self-seeding let it climb over and smother neighbors and reappear as volunteers for years. Deadhead before seeds ripen to limit self-sowing and pull volunteers early to keep it in check.