How Deep Do You Plant Gladiolus?

Sizes of Corms

• The most vigorous growth and large flower spikes develop from the largest gladiola corms. Corm size affects planting depth. Large corms measure roughly 3 to 4 inches wide and 3 inches tall. Corms just over 1 inch in diameter are considered medium-sized and are the minimum size required for the production of a flower spike. Small corms are 1/4 to 1 inch big, and cormlets or cormels are pea-sized immature corms that remain around the base of the largest, "mother" corms by the end of the growing season. Often corms are sold with size ratings. Jumbo is the largest corm, followed in decreasing increments from number 1 to number 6, the smallest.

Planting Depths

• Generally speaking, plant gladiola corms between 3 and 6 inches deep. The larger the corm, the deeper you need to plant it. Use your judgment and group corms by approximate size so you plant them at the best depth. For jumbo and other large corms, dig the hole 6 inches deep and place the pointed side of the corm upward on the soil. Use a planting depth of 4 to 5 inches for medium-sized corms, and about 3 inches for small corms. If you are propagating your own corms, and choose to develop cormels into larger corms, plant cormels only 1 to 2 inches deep.

Spacing

• Avoid planting gladiolas too close to each another. Cramped corms compete for the same moisture and nutrients in the soil. As the plants grow, their foliage may shade each other or limit air circulation that leads to fungal or pest problems. Whatever depth you plant, that also becomes the spacing between corms. For example, if you plant the corm 6 inches deep, space multiple corms 6 inches apart from each other in the planting area.

Soil Texture Issues

• Gladiolas prosper in a crumbly, organic-rich garden soil. It's best to dig the planting area with a shovel to a depth of 12 inches prior to planting the corms. This gives you the opportunity to add compost or other soil amendments that benefit the glads. In regions with a heavier clay soil, plant all corm sizes slightly shallower. Conversely, if your garden soil is light and sandy, consider planting each size slightly deeper. Heavier soils drain more slowly, whereas sandy soils drain quickly. Adjusting planting depth ensures the ideal conditions for the corms. Also, planting too shallow in a light soil leads to tall plants toppling in winds or when the heavy flower spike opens.