Gladioli originate from South Africa and are members of the Iridaceae family.
The botanical genus ‘gladiolus’ is from the Latin for a ‘Small sword'
They come in a wide range of sizes and colours.
The sizes range from the 35mm (1½”) miniatures, to the giant flowered types, which can be up to 175mm (6½”) across.
The spikes can grow up to1800mm (6ft) tall.
The colour range covers all the colours of the rainbow and a few more besides, such as pink brown and grey.
Add other attributes such as; coloured blotches and stripes, picotee edges and you have a veritable kaleidoscope of colour.
Gladioli are bulbous plants; this is where the base of the plant is swollen into a food storage organ that enables the plant to survive when dormant.
Unlike a daffodil which is formed from a ‘true bulb’, gladiolus are produced from a ‘corm’.
To explain; true bulbs are formed from fleshy leaves and frequently consist of concentric rings of scales attached to a basal plate, whereas ‘corms’ are formed from the swollen bases of stems and are replaced by new corms every year.
When purchasing stock; it is advisable to get it from a recognized gladioli supplier.
What you should look for is plump high crowned corms with small root scars that are about 1½-2” (40-50mm) in diameter.
Note; Some supplier indicate the girth of their corms rather than the diameter when advertising their stock, so the above sizes would translate to; 5”-7” (125mm-175mm)
Avoid large flat corms with large root scars.
- Large flowered: - 100mm to 175mm across.
- Small-flowered or Butterfly group: 50mm to 100mm across.
- Primulinus: 50mm to 75mm across.
- Miniature: 35mm to 50mm across.
The best time to cut stems for arrangements is when the first (lowest) bud is opening.
Immediately after cutting, stand the stems in at least 300mm (12”) of water.
Week 4; Check the corms occasionally during the winter and discard any that show signs of disease.
Week 12; Propagate gladioli from cormlets / spawn.
This is the main method used to increase a particular gladiolus cultivar.
It is also the cheapest and easiest method to increase stock, and as it is vegetative propagation, the flowers produced, will be identical to the parent plant.
Cormlets are the tiny mini corms found around the parent corm.
These can be detached and cleaned, then stored in a dry, frost free place, in paper envelopes.
Cormlets are best sown as early as possible after collection in a nursery bed providing the soil is warm.
Alternatively; small quantities can be sown in boxes or pots.
To prevent infection from disease, it is better to use ground that has not grown gladioli for a few years, or use sterilised potting compost if they are to be grown in pots/boxes.
Before planting it helps if the outer brown skin or husk is removed, or at least cracked by pressing the cormlet gently between your finger and thumb.
Some growers soak the cormlets overnight in lukewarm water to assist with germination.
Sow the cormlets on a thin layer of sharp sand (to assist drainage), in rows 50mm (2”) deep and 50mm (2”) apart, (a little deeper if the cormlets are quite large), the rows should be at least 100mm (4”) apart.
Label each cultivar as necessary.
Signs of growth should appear in one to four weeks dependant upon variety.
Throughout the growing season; never let the young plants dry out, and take the usual precautions against pests and diseases.
It is also important to keep the area weed free, the young plants do not want any competition for nutrients at this stage.
Some cormlets, may try to flower in their first year.
It is better that these small flower spikes are cut off, so that the plants energy is put into corm formation.
Harvest the corms as soon as the foliage begins to die back.
If the leaves remain green do not leave them any later than the end of September or early October.
Cut the foliage off as close to the corm as possible, and trim the roots.
Allow the cormlets to dry off in a dry airy spot that is out of direct sunlight.
After drying, normally two to three weeks, clean the small corms and store them as recommended for the large gladiolus corms.
Subject to the size of the cormlet after the above treatment, they may require a further year of the same treatment before they are of flowering size.
Week 14; To obtain earlier flowers place the corms on top of pots or cell trays filled with potting compost at a temperature of 13°C (55°F)
The corms will soon sprout and can then be planted out during May in the usual manner.
Watch out for aphids infesting the young sprouts.
Note; At planting out time take great care not to break the brittle root system.
Week 15; or as soon as the soil is workable prepare it for planting by digging in copious amounts of well rotted* organic matter.
* It is crucial that the organic matter is well rotted!
Too high Nitrogen content may cause problems later on in the plant's development.
Rake in bonemeal at the rate of 80-100gms (3-4oz) per sq.m
Week 18; Plant out batches of corms at fortnightly intervals from now until Week 26 to extend the flowering season.
Note; A sign that is often used in determining a safe planting out time is to plant out when deciduous trees have come in to leaf.
Gladioli appreciate well drained soil but can be grown in heavier soils if planted within a pocket of sharp sand or gravel, this procedure will the drainage qualities of the soil.
As mentioned previously; plump, high-necked corms with a small root scar produce better plants than the larger, fatter corms with a broad root scar.
Prior to planting check if the corms are dormant or not, dormant corms should never be planted!
The method of checking is to look at the basal scar for evidence of root nodules.
Note; The fact that the corm may have developed shoots at the top of the corm should not be taken as a sign that they are ready to plant out, always look at the root scar for signs of root formation.
Dormancy can often be induced by subjecting the corms at a temperature of 21°-24°C (70°-75 °F) for a few days.
Space out corms according to type and always remember that gladioli are gross feeders, so if growing for exhibition purposes allow wider spacing.
Corms can be planted in trenches or individual holes and should be planted 100mm (4”) deep in heavy soil, and 150mm (6”) deep in light soil .
On heavy soils; place corms on a drainage layer of sandy compost.
Do not plant too shallow or the plants may topple over when in full bloom.
A simple way to work out suitable spacing is to divide the ultimate height of the plant by 6, e.g. 1200mm (4ft) high divided by 6 equals 200 mm (8") apart.
n.b. If the height is unknown; plant out 200-300mm (8"-12") apart.
Small-flowered or primulinus gladioli can be set 150mm (6") apart.
Plants may need some support (circa week 30) to prevent stem damage, particularly if growing in windy positions.
Week 22; Do not hoe or apply fertiliser until the young shoots appear, usually 2-4 weeks after planting out.
Apply a light top-dressing of fish manure around the young shoots.
Hoe often, to check weed growth and to aerate the soil.
Note; Hoe very shallow to avoid root damage.
Plants will require additional feeding throughout the season.
This feeding can take the form of either chemical or organic fertilizers.
A balanced feed given at regular intervals will suffice for initial growth.
This should be followed with a high potash feed being applied as the flower spike develops.
This will strengthen the spike and enhance the flower colour.
Week 23; Keep a look out for pests such as thrips (thunder flies) and red spider mite, treat as necessary.
Similarly keep an eye for Virus disease!
These are usually quite difficult to detect in early growth.
A couple of signs are; when a plant develops yellowing or mottling foliage or grows in a curved manner rather than upright, the whole plant should be removed and destroyed by burning as soon as possible.
Avoid applying sprays to opening blooms, especially in bright sunlight.
Week 28; Withhold water until secondary roots have formed, eight to ten weeks after planting.
After that, water generously, particularly during dry periods after the flower spike has appeared.
Gladioli must never want for water, particularly from the time the first flower spike shows.
Lack of water at this stage will result in shorter flower heads.
Give at least 1 gallon (4.5 litres) per four to six plants.
Staking is usually unnecessary, except for the large-flowered hybrids or if the plants are grown in exposed positions.
Flowers should be cut with a minimum of damage to the foliage leaves.
Ideally leave a minimum of four leaves to feed and water the new corm forming underground.
Week 41; Lift the plants.
Lift gladioli with a fork when the foliage begins to turn yellow-brown or six weeks after the last flower fades.
Take care not to bruise the corms.
Remove any soil sticking to them, and cut off the main stem 25mm (1") above the top of the corm.
After lifting, batch up named varieties with an identification label.
Allow them to dry in a warm room with good air flow, at a temperature of around 70°F for two to three weeks to allow curing to take place; this time will vary with corm size etc.
Week 42; onwards; Prepare for next year by digging the beds, and forking in well rotted garden compost or farmyard manure.
Week 43; If the corms a fully dry break away and discard the base plate (previous year’s corm)
Remove the small cormlets and store these separately if they are wanted for propagation.
Check at this stage for any signs of disease an discard affected corms.
Removal of husks encourages loss of moisture, so it is better to remove the dirty outer shell only.
Once cleaned, store the corms with the root scar downwards in a dry airy place, with a minimum temperature of 10°C (50°F)