Dame Everage must be pleased as punch that her beloved blooms are making a comeback. I once abhorred these flowers, but I’m slowing coming around. Today’s hybrids have gorgeous colours – rich purples, deep reds, lavenders, lime greens, rosy colours and the prettiest pastel pinks. There are bi-coloured blooms too – flowers with blotches, stripes or picotee edges – and a choice of ruffled, waved or frilled petals in large-flowering or petite forms.
Gladioli are excellent cut flowers and will bloom over several months if you stagger the planting. But the quality of flowers depends on the quality of the corms. Plump, high-neck corms with small root scars (at the base of the corm) produce far superior blooms than flat, wide corms with large root scars. So choose your corms by depth rather than width.
If you buy corms at the end of the season, make sure they’re still firm and not soft or dehydrated. New root buds may be forming, which is fine, but don’t select corms that have long dried roots.
When you get your corms home, store them in a cool, dry place with good ventilation until ready for planting.
In the Garden
Gladiolus corms can be planted any time from now up until December. Plant pointy side up in full sun and well-drained soil, 15cm deep and 12-15cm apart. If you plan to cut your glads for indoors, you can plant them closer. Cut flower growers often space them as little as 5cm apart.
Tall plants may need staking. If you only have a couple of plants, then stake them individually. If you have several, a framework of stakes with twine trussed in between them is ideal.
Keep your plants well watered in summer. Lack of moisture often results in shorter spikes and smaller flowers – not to mention smaller corms the following season.
It may also result in skew-wiff plants, says Paul Hoek of NZ Bulbs.
“Infrequent water leads to bent spikes as the plants go through rushes of rapid growth. Water regularly to keep them just moist.”
Mulch around plants in summertime to maintain consistent moisture levels and keep weeds down, which compete for water.
Gladioli do not need a lot of feeding through the growing season, but if you do feed, says Paul, avoid fertilisers that are high in nitrogen.
“Never use animal manure on gladioli – the high level of nitrogen greatly increases the chance of fusarium rot developing on the corms.”
In warmer areas, gladioli corms can be left in the ground to overwinter, but where frosts are expected, lift them about six weeks after flowering and cut off the tops about 2cm above the corms. Brush off excess soil, then dry the corms for a couple of weeks or more in a warm, well-ventilated room before removing the old ‘mother’ corm. The mother corm shrivels and dies each year but one or more new corms form on top of it during the growing season. These can be planted the following season.
Tiny corms, known as cormels, also develop on the new corm. These can be removed and stored, ready for planting in spring, although they will need a couple of seasons in the ground before they’re big enough to flower. You could grow these in a separate bed in the meantime until they reach flowering size. They needn’t be planted deep – around 3-5cm will do the trick.
Store your corms in a cool, dry, airy room in a mesh bag or slatted tray. Warm conditions or non-ventilated rooms cause early sprouting and root growth.
Gladioli attract thrips and aphids. Thrips are a real pest, becoming more active in hot dry conditions. Like aphids, they feed by sucking plant sap. If left unhindered, they congregate in large numbers on leaves and inflict damage that causes discoloured leaves (brown or a mottled silver), misshapen flowers, and flowers that are marked or fail to open. Plants that are stressed from lack of moisture attract both thrips and aphids, so make sure you water regularly.
A spray may be necessary to keep them under control if numbers are high. Or you can try placing a blue sticky trap nearby to catch them – or at least detect them in the early stages. Thrips are often not discovered until they’ve built up huge numbers and inflicted a good deal of damage on plants.
Make your own blue sticky trap by attaching pieces of blue cardboard smeared with petroleum jelly on sticks around your plants. Commercial growers use these to detect the presence of thrips, whereupon they release beneficial insects to devour them.
Thrips also live in amongst weeds, so keep on top of these and you will remove their natural habitat.
Thrips can overwinter on stored corms, and aphids may attack them, so it’s a good idea to spray the harvested corms with a solution of Confidor insecticide, says Paul. “This is long-lasting and will protect the corms not only from aphids while in storage, but will also control any thrips that may winter over on the corms.”
Plant your gladioli in a different spot each year to get on top of thrips. This is also a good way to prevent diseases, such as Fusarium wilt, taking hold. If plants are stunted and leaves wilt or turn yellow, your glads may have succumbed to wilt or some type of virus. Dig them out and destroy them, then plant new corms in a different spot next year. Diseases can remain in the soil for several years.