For best results planting up the corms first in a container and then transferring them into their final flowering positions in mid-May may be a better option especially if the ground is wet and cold in your area when your plants arrive. Water well throughout the growing season, and lift the corms at the end of the season when the leaves turn yellow-brown and store them in a cool, dry, frost-free spot over the winter months.
In a container Plant the corms 10cm apart and 20cm deep in a multi-purpose compost and water in. Place in a bright, frost-free spot. If you are going to keep the gladioli in the pot/container all summer, place a stake in the pot at the time of planting the corms to avoid damaging them. Generally, plant 5 corms per 15cm pot.
If you are then transferring the Gladioli into the garden, carefully take the whole thing out of the pot and plant the clump into a freshly dug hole in May. Gladioli are hungry plants so to get them to flower well, feed them regularly (once a fortnight) with a high potash feed once the flower spikes are approx. 15cm high and continue until the flowering season is over.
In the garden border if you are planting the corms straight into the border in spring, choose an area that has been previously enriched with well-rotted manure, as Gladioli like a rich soil but one that is well-drained too. If the ground is wet, plant the corms 10cm apart and 10-15cm deep onto a bed of sharp sand or horticultural grit to help with drainage.
Gladioli are hungry plants, so to get them to flower well, feed them regularly (once a fortnight) with a high potash feed once the flower spikes are approx. 15cm high and continue until the flowering season is over.