Gladiolus are one of the most spectacular cormous plants that can be grown in most gardens. Other than the fact they are so colourful, a big plus point in their favour is that they take up so little room for such a splendid display of flower from mid summer through until autumn.
The big disadvantage of gladioli bulbs, being that they are also splendid cut-flower material. Not a problem for some!
There are three main groups of Gladiolus for growing in gardens.....
Gladioli bulbs are actually classical textbook corms, in that the corm is an underground stem - modified as a storage place for the dormant season. With your Gladiolus corms, you will probably see a few 'buds' situated around the corm. The main flower stem is sent up from the centre of the top of the corm. Once the flower stem and foliage starts to grow above ground, it forms a new corm on top of the one that you have planted. The original corm dies off, and should be removed when storing for the winter.
In milder areas - and certainly those that have only the lightest of frosts, the corms can be left in the ground over winter. Far better though, to lift them and store for the winter.
Planting Gladiolus Corms. The corms should be planted in spring at a depth of around 5-6in and preferably with a bed of sharp sand or grit under the corm. Plant after all frost have gone, unless in a mild frost area. They can be covered with a fleece or mulch for late frost warnings. Gladiolus prefer a well drained sandy soil, but will grow well in any situation that does not become waterlogged - especially in winter if the corms are left in the ground. The corms can be planted either as single dot specimens in borders and beds - remembering of course that whilst they require little space at ground level, some Gladiolus will grow to a height of a metre - or even more!
Gladioli bulbs should be planted in full sun, and in exposed areas, it might be a good idea to insert a cane or other support at planting time. This will serve the purpose of alerting you to where you have planted the corm, and also to support the sometimes top-heavy flowering stems.
Feeding and Fertilizer. The original corm will provide the food source for the first growth of the Gladiolus - even until it is around 12in tall. However, it will then need a good supply of nutrient to start growing the next corm - at the same time of growing and flowering the above ground stems. This period is very important for the development of the new corm which will be in essence, next year's plant.
Regardless of soil type, a regular liquid feed - Tomato feed or general feed - should be applied weekly until after flowering has finished. Feed should be applied when the soil is moist and not when dry. Watering for a few hors before will suffice.
Growing Care of Gladiolus. Whether or not the flower stems are cut for indoor display, or are left on the plant for garden display, the foliage should be allowed to die naturally and dry off before the corms are lifted. Simply pulling the plants out of the ground and leaving to dry in the sun is not a good idea.
Storing Gladiolus for Winter. Once the foliage has died down - and before the risk of frosts, carefully fork the plants out of the ground and cut the old stems back to within a few inches of the ground. The stems may simply pull away from the corm. Remove the old withered corm from the base of the newly formed corm and dispose. It has fulfilled its function. It is of no further use. Allow the corms to dry - either in full sunshine, or in a light place in garden shed. After the papery skin has formed (do not peel it off) the Gladiolus corm can be stored in a dry frost-proof place. Placing the corms in a seed tray and covering with dry peat is ok. A few sheets of newspaper laid over the top will also be suitable.
Best method of propagation is to remove the small cormlets that appear around the base of the corm whilst it is dormant. These can then be planted out in the spring and be allowed to grow for a two years before flowering of any consequence starts. Don't forget to lift them in the Autumn - as above,
In storage, Gladiolus corms may be subject to one of several moulds that can rot the corm. Inspect every few weeks or so to combat this. Yellow Sulphur powder puff is a good idea at time of storage.