Known for their impressive flowers on tall stems, gladiolus is the perfect addition to any cut flower garden. Even if you’re not growing them to cut and bring indoors, they still add plenty of ornamental value to perennial beds, producing masses of colorful flowers in summer.
Growing from corms, gladioli are relatively easy plants to care for, especially for those in warmer climates. To add these intricate blooms to your garden, follow this easy guide.
Gladiolus Plant Overview
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What Is It?
Gladiolus boasts diverse species and hybrids with sword-shaped leaves and vibrant flowers.
Gladiolus is a stunning genus in the Iris family – Iridaceae – known for its large and intricate flowers. Often affectionately known as glads, a shortening of the genus name, there are around 300 species and even more hybrids and cultivars to choose from. In other words, gardeners won’t have trouble finding a unique type they will fall in love with.
The genus name Gladiolus is derived from the Latin for sword, aptly describing the plant’s sword-shaped leaves. This unique leaf shape does provide ornamental interest, but the plants are most appreciated for their tall flower spikes in a range of eye-catching colors.
Gladioli are long-established plants growing in several warm regions, from Southern Africa to the Mediterranean. Many species are native to the Cape in South Africa, but there is plenty of diversity between species worldwide.
Understanding your species and its native region is key to care, although most gladioli grown in home gardens today are hybrids. The plants are quite resilient, making them ideal for beginners looking for a low-maintenance addition to perennial beds.
Characteristics
Gladioli, prized for their tall spikes of trumpet-shaped flowers, enhance gardens and arrangements.
Gladioli are appreciated for their height and tall spikes of colorful flowers. These flowers can reach up to 6 feet in height, instantly becoming a central feature in any planted bed.
The individual flowers, often shaped like trumpets, open slowly from the bottom up to maximize flowering time and color benefits. The narrow foliage surrounds the flower spikes to provide a green backdrop that complements while allowing the colorful flowers to shine.
These plants are often mixed with other perennials and annuals for varied texture and height in beds. However, they also look great as a backdrop, especially when planted in large groups of different colors.
Their impressive height and striking blooms are also popular for cut flower arrangements. Long stems and lasting blooms make them ideal for tall vases and creative displays, whether for a special occasion or just to decorate your home and bring a touch of the outdoors in.
Planting
Plant gladiolus corms in spring after frost, in well-drained, sunny soil for summer blooms.
The best time to plant gladiolus corms is in spring after any chance of frost has passed to avoid damage to new and cold-sensitive growth. Getting them in the ground at this time should deliver flowers by mid to late summer.
Choose a bright spot in your garden with a full day of sun and rich, well-draining soil. Avoid planting in heavy clay, as this can cause the corms to rot before new growth even appears. If you are dealing with clay, amend generously with compost to improve structure before any planting is done.
When planting, dig a hole around 5 inches deep and bury it with the root side down. If you’re planting a few at once, give them around 5 inches of space (preferably more) between each corm. After planting, fill the gaps with soil and water lightly to promote root growth.
You may consider staggering your planting times for more flowers throughout the summer. Plant corms two or three weeks apart, extending the blooming season from mid-summer onwards.
How to Grow
Gladioli are not needy plants, especially if you plant them in the perfect spot. Monitor these conditions to provide the perfect care, ensuring a flush of flowers each season.
Light
Gladioli thrive in full sun, requiring at least six hours daily for optimal blooming.
Gladioli are dependent on the full sun to flower successfully. Aim to give them at least six hours of full sun per day – preferably more – to ensure they have all the energy required to bloom.
In hotter climates, these plants can benefit from a spot with some afternoon shade to avoid intense scorching during the hottest parts of the day. This also helps mid and late-summer flowers last much longer on the plants before wilting.
Water
Keep gladioli consistently moist after planting for strong roots, reducing watering as they establish.
Soon after planting, gladioli need consistent moisture. Regular watering will help them develop the strong root system and support required for flowering. This should continue well into spring until the plants are well-established, when you can slow down on watering.
The soil should be kept evenly moist but never soggy to promote growth and support the tall stems. Overwatering (or, more likely, poor drainage in the soil) can quickly lead to rot, a common issue that will kill the entire plant before it can flower.
During times of drought or extreme heat, don’t forget to water the plants deeply. This will prevent stress and wilting that can impact flowering later on. Monitor the rain forecast to decide on a sufficient watering schedule.
Soil
Provide gladioli with rich, well-draining soil, slightly acidic to neutral, enriched with compost.
Gladioli are not majorly fussy about the ‘perfect’ soil, but giving them the best start will always improve flowering later on. Aim for rich, loamy soil with a slightly acidic to neutral pH for the best results. The only essential criterion is that it drains well to avoid corm rot.
Improving quality with organic matter like compost is recommended regardless of your soil type. Additional compost will enhance drainage airflow and nutrient availability while retaining moisture to promote strong growth. Mix the compost into your soil well before planting, spreading it evenly around the beds.
Temperature and Humidity
Gladiolus prefers moderate to warm climates, hardy in USDA zones 8-10, with frost precautions.
Gladiolus thrives in moderate to warm climates, with some variation depending on your species.
While some hybrids are hardier than others, they generally don’t like frost, growing best in USDA zones 8-10. Gardeners in zone 5 and above should plant Gladiolus nanus for its hardy nature, although it must be mulched throughout winter to regulate soil temperature.
In colder regions, dig up gladiolus corms before the first frost in fall and store them indoors during winter. They will be ready to plant out the following spring once temperatures have warmed and no more frost is predicted.
Those in high-humidity areas may want to plant their gladioli slightly further apart to promote airflow and limit issues with fungal disease. Beyond that, these plants are not fussy about humidity levels.
Fertilizing
Boost gladioli before flowering with low-nitrogen fertilizer and prioritize soil improvement with compost and mulch.
Although they can produce flowers without extra feeding in the right soil, a boost just before flowering can help struggling plants. Use a fertilizer lower in nitrogen to boost leaf growth when flowers should be the primary focus.
If your soil lacks nutrients, consider applying a slow-release fertilizer soon after planting. However, this short-term fix shouldn’t replace long-term soil improvement. Amend the soil with compost and continue to apply organic mulch throughout the season to slowly improve soil quality over time, limiting your need to fertilize.
Maintenance
Carefully brush off the dirt, dry, and store corms, applying fungicide if desired.
Tall gladiolus varieties usually need staking (especially when planted in wind-prone spots) to prevent the flower spikes from bending. Install your stake as green growth emerges, but before the leaves become too tall to avoid damaging the root system.
Deadheading is also recommended to support new flowers rather than fading ones. This preservation of energy also aids in the development of the corms for the next season.
After blooming, allow the foliage to die back. The plant will slowly store resources in the corm to give it the energy to sprout again the following season. If you cut them back too early, they may struggle to flower the next year. Once the foliage turns yellow and fades after frost, it can be cut back.
If you’re lifting the corms to store them, pull them carefully to prevent damage. Brush off the dirt, trim the main stem, and allow them to dry for a few days before placing them in a mesh bag. You can also apply a protective fungicide before storing to limit the chances of disease in storage.
Propagation
Propagate gladiolus in the fall by separating cormlets from mature corms.
If you dig up your gladiolus, you’ll see small cormlets develop around the base. These can be used in propagation to grow more of the same variety of your favorite plant.
The best time for propagation is in the fall after the foliage has died back and the corms have completed their growth cycle – when you would lift them for storage. Carefully dig up the corms and gently separate the new corms and cormlets from the old ones.
After separating, dry each corm in an airy and dry spot for a couple of days. Wait until the outer skin has hardened slightly, protecting the corm from problems with pests and diseases like rot when storing.
When spring arrives and the soil warms, plant these corms as you would normally. Remember that while the larger corms (around 1.5 inches in diameter) will likely flower in the first year, the smaller cormlets will take a couple of years to produce blooms.
Common Problems
Growing gladiolus is not difficult, but there are a few issues to watch out for, both within and out of your control.
Corm Rot
Prevent gladiolus issues by improving the soil with compost and checking for good drainage.
One of the most common problems with gladioli is caused by planting in poorly draining soil or watering more than needed. It can also be caused by excessive rain, which can only be mitigated by improving soil drainage. Amend the soil with compost to improve conditions, and never water when the soil is still moist.
Pests
Watch for thrips, mites, and caterpillars on gladioli.
Thrips are the pests to look out for when it comes to these plants. These tiny insects feed on both flowers and foliage, leading to streaky leaves and deformed flowers. Other potential pests include mites and caterpillars.
Regularly inspect your plants for signs of damage and treat them as soon as possible. Hand-picking can work for some pests, but for severe problems, insecticidal soap or horticultural oil may be needed.
Diseases
Prevent gladiolus rust and fusarium with proper spacing and watering at the soil level.
Look out for diseases like gladiolus rust, which causes spots on leaves and flowers, and fusarium, which results in yellowing and wilting of leaves. Good spacing for air circulation and avoiding overhead watering can aid in preventing these diseases. Remove infected plants quickly to prevent the spread of the problem to other healthy plants. Destroy them and don’t compost, cleaning any tools you’ve used as soon as you’re done.
Environmental Stress
Protect gladioli from damage in extreme conditions by staking and mulching for temperature control.
Extreme conditions like high winds can damage the tall spikes of these plants. Extreme heat or cold can also affect their growth and blooming. Manage the environment by supporting the spikes with stakes and mulching to regulate soil temperature.
Frequently Asked Questions
Each gladiolus corm can produce additional smaller cormlets around its base. Over time, these cormlets can grow into flowering plants, gradually increasing the number of gladiolus plants in your garden. However, this is a very slow process, and these plants do not spread aggressively or quickly. To control or expand your gladiolus collection, you can dig up and replant these cormlets to improve spacing. Depending on their initial size, you will see flowers on these new plants within a few years.
Most gladiolus varieties are not frost-hardy and will not survive harsh winters outdoors in colder climates. However, a few hardier species, like Gladiolus nanus, can withstand colder temperatures. For the more common gladiolus varieties, dig up the corms in the fall and store them indoors over winter to replant in the spring.
Gladiolus typically blooms in mid to late summer. The exact timing of blooming can vary based on the planting time and local climate conditions. Plant corms at intervals of two to three weeks for a continuous display of blooms.
Gladiolus plants are toxic as they contain substances known as alkaloids, which can cause symptoms like drooling, vomiting, lethargy, and diarrhea in pets. Keep gladiolus out of reach of pets, especially dogs and cats, to avoid accidental ingestion.
Final Thoughts
If you’re looking for a new member of your cut flower garden or just want a tall, reliable perennial for your beds, gladiolus is a great choice.
