How to Grow Gladiolus in South Africa

The complete guide to watering, feeding, pests, and diseases

Gladiolus are iconic summer bloomers in South African gardens. Their tall, colourful spikes make them perfect for garden beds, borders, and cutting gardens. Although they look elegant, they are surprisingly easy to grow once you understand their basic needs.

This in-depth guide is written specifically for South African gardeners who want strong, tall stems, bright colours, and healthy corms year after year. We focus on the three areas that matter most: watering, feeding, and preventing pests and diseases.

Jumbo Gladiolus Bulb

Understanding the Gladiolus Growth Cycle

Gladiolus grow from corms, which produce a brand-new corm and some small cormlets every season. The old corm shrivels as the new one forms on top of it. The bigger that new corm becomes, the better the plant will perform the following year.

This means your care throughout the season should support:

• Strong root development

• Steady stem and leaf growth

• Protection from pests

• Enough time for the new corm to mature

Everything from watering to pest management plays a role in forming next season’s corm.

 

Planting Gladiolus Correctly

Choosing the right location and method for planting is crucial for the success of your plants. It's important to consider factors such as sunlight exposure and soil quality when deciding where and how to plant your gladiolus. It can make all the difference in how well your gladiolus do.

Choose the Right Location

Gladiolus prefer:

• Full sun (at least 6 hours)

• Well-draining soil

• Good air movement

If your soil is heavy or clay-based, loosen it by adding compost and coarse sand. Glads hate standing water.

Planting Depth and Spacing

• Plant corms 5 to 7cm deep.

• Space them 10 to 15cm apart.

• For continuous flowering, plant new batches every two weeks.

Prepare the Soil

Before planting, work in:

• Compost

• Bonemeal or superphosphate

• A handful of general fertiliser if your soil is poor

Healthy soil is the foundation for tall, sturdy stems.

Gladiolus Bulbs ready to be planted

How to Water Gladiolus Properly

Proper watering is crucial for gladiolus care. Too much water can result in rot, while too little water can lead to weak stems and undersized blooms.

Stage 1: Sprouting (First 2 Weeks)

After planting, water deeply once. Then keep the soil slightly moist until shoots appear. Avoid constant watering, which can rot the corms.

Stage 2: Active Growth

Once shoots start to  appear, glads need consistent, deep watering.

Guideline for South Africa:

• Mild weather: 20–30 mm per week

• Hot inland areas: up to 40 mm per week

• Sandy coastal soils: water more frequently but not heavily

Deep watering encourages strong root systems and keeps stems upright.

Stage 3: Flower Spike Development

Moisture is critical during this stage. Any water stress will reduce spike length and flower size.

Stage 4: After Flowering

Do not stop watering immediately after flowering. The plant still needs moisture to form the new corm. Only reduce watering in autumn once the leaves naturally turn yellow.

Watering Tips

• Avoid shallow daily watering.

• Water early in the morning.

• Mulch to reduce heat stress and moisture loss.

• Never allow gladiolus to sit in soggy soil.

First sprouts poking through the soil

Feeding Gladiolus for Best Results

Glads are very heavy feeders. Feeding correctly leads to thicker stems, bigger flowers, and healthier corms.  It is crucial to continue feeding after flowering to ensure the plant stores sufficient reserves for the next season.

Before Planting

Work bonemeal into the planting area. This is important for early root development. 

Also apply a balanced starter fertilizer when you plant to kickstart your plants. We use a Wonder All Purpose Starter 2:3:2 when we plant our glads. Lightly work it into the soil before planting,

Mid-Season Feeding

It is good practice to feed again when the flower spikes start to form.  For this feeding we use our own Dahlia Doepa which is low in Nitrogen and promote stem stems, flowers and corms.

Feeding Rules

• Always water deep after fertilizing your plants.

• Do not use high nitrogen fertilisers.

• Do not place fertilizer directly on the corm.

 

Staking and Supporting Tall Gladiolus

Some varieties of gladiolus grow very tall especially those sold for cut flower purpose. Tall stems often need support, especially in windy areas.

Good options include:

• Bamboo stakes

• Wooden stakes

• Garden netting

• Recycled branches

Insert stakes at planting time so you do not damage the corms later. Tie stems loosely with soft ties.

 

Common Gladiolus Pests in South Africa

 

Thrips

The most common gladiolus pest. Thrips cause streaky leaves, brown petals, and deformed flowers.

Thrips damage to Gladiolus Flower

Signs of Thrips:

• Silvery streaks on leaves

• Brown stripes on petals

• Flowers that do not open properly

Control:

• Start preventive spraying early

• Use neem oil or a pyrethroid spray

• Rotate insecticides

• Remove old plant debris at season’s end

Aphids

Aphids typically cluster on tender growth and suck the sap from new growth, especially on flower buds.  They also are able to spread viruses to other plants.

Aphid infestation on gladiolus leaves

Control:

• Neem oil

• Insecticidal soap

• Encouraging ladybirds

• Spray of the plants using strong water spray

Cutworms

Cutworms lives under the soil and cut young shoots just under at soil level.

Cutworm eating a plant stem

Control:

• Use cutworm insecticide around new plantings

• Keep beds weed-free

• Avoid problem areas previously used for leafy vegetables

Slugs and Snails

Slugs are common in moist coastal and shady humid areas of other gardens.

Control:

• Safe slug pellets

• Morning watering

• Reduced mulch in problem areas

 

Gladiolus Diseases in South Africa

Fusarium Corm Rot

A fungal disease causing brown, soft, smelly corms.

Image of Fusarium Corm Rot

Prevention:

• Plant only healthy corms

• Good drainage

• Dust corms with fungicide before planting

• Rotate planting areas yearly

Botrytis (Grey Mould)

Common in damp or humid weather.

Botrytis on Tulip leaves

Signs:

• Soft grey mould

• Flowers rotting before opening

• Leaf spotting

Control:

• Improve spacing

• Morning watering

• Remove infected plant material

• Avoid overhead watering

Mosaic Virus

Spread primarily by aphids.

Signs:

• Streaked or mottled leaves

• Distorted flower spikes

Important:

There is no cure. Remove and destroy infected plants.

Harvesting Gladiolus for the Vase

Harvest when the bottom two or 3 florets show colour.

Cut the stems early in the morning.

Cut by inserting a sharp knife above the second to fourth leaf and making a slanting cut up the stem.

Leave at least two to three leaves on the plant to feed, so the corm can mature properly. .

Immerse the stems in clean water immediately to avoid wilting. Gladioli are extremely geotropic, so store in a vertical position to avoid curved stems.

 

Aftercare and Lifting Corms

Once the plant finishes flowering, ensure that you provide the necessary nutrients and water during the rest of the growing period to support the development of a healthy new corm. Let it die back naturally. The longer the plant has to grow after flowering, the stronger the corm will be. 

 

When to Lift

You can lift corms if:

• Your soil holds too much moisture

• Thrips were a big problem

• You want to sort and store corms for next season

• You garden in very wet winter areas

Lift gently, remove the old mother corm, and allow the new corm to dry before storing in a cool, dry place.

White Prosperity Gladiolus

Final Thoughts

Gladiolus bring height, drama, and colour to any South African garden. With consistent deep watering, the right feeding routine, and a proactive approach to pests and diseases, you can enjoy strong, healthy flower spikes year after year.