Lee W. Miller

UCCE Master Gardener San Joaquin County

 

Gladiolus (Gladiolus x hortulanus) is a member of the Iris family and is easily grown and will reward the gardener with awesomely beautiful flowers.   The gladiolus takes its Latin name from the sword of gladiators which it resembled, but they are often given the short handle-glads. The plant is native to mild climates in Asia and Africa, but the modern cultivars, developed from South African species, are grown on all continents.  Gladiolus grows from corms which can be purchased at garden centers and nurseries in the winter and spring or from catalogues or online suppliers. The North America Gladiolus Council maintains a website on growing glads which also lists several suppliers, nomenclature, and tips on growing: http://www.gladworld.org/growing.htm. 

It is helpful to know the classification system often used in catalogue listings of glads. Usually the variety name is listed followed by the name of the person who hybridized the cultivar and date of its introduction, a size and color code and the approximate days to bloom. For example, here is the information on one of my favorites: PRISCILLA (Frazee '77) (465) 75 days. The number 465 indicates size and color. The size is indicated by the 400, 400 being large, and the color by the 65, indicating a medium rose.  The color range for rose is 60 to 66 with light rose=60 and dark rose=66. Other sizes and colors are coded similarly.  For a full treatment of this system, see p. 62 of the reference book below or the online reference listed above. However, the variety of coloration in glads is best observed in pictures and many are displayed on websites. 

Gladioli corms are graded by size. Large is greater than 1.25 inches; medium is 0.75 to 1.25 inches, small is less than 0.75 inches. Large corms produce larger flowers. Planting time is from January through early May.  In much of California, there is no danger that they will freeze in the ground in winter, so they can remain there year round. However, in colder zones they need to be dug and stored away from freezing temperatures preferably in the lower part of the range 38-58°F.

 

 Gladiolus does best in full sun though they tolerate part shade.  A well-drained soil with a pH range of 6.5-7.0 is optimal but they are not fussy with regard to soil type or fertility and can grow in a wide range of soils. If you can grow vigorous weeds or vegetables you can grow gladiolus. It is good to shelter them from strong winds as the 3-5 ft stalks are subject to lodging which can spoil the flower spike.

 

Rototilling, plowing, discing or deep digging the soil to a minimum depth of 8 inches is important for having the soil in proper tilth for growing gladiolus.  Compost or manure that is well aged and mixed into the soil will condition and fertilize the soil. Organic material that is not well aged should be worked in a few months in advance of planting.

 

Planting in borders usually involves planting a dozen or more corms in a small concentrated area with 4 inches between corms. They can also be planted in large containers.  Such plantings are likely to be more striking if only one color is used.

 

Glads can also be planted for harvest as cut flowers.  For cut flowers, corms are planted in rows in the vegetable garden. I plant double rows about 8-10 inches apart with 4-6 inches between corms within each row and I use a soaker hose in the row to irrigate. Each double row is about 30 inches from its neighbor to provide a walkway. I insert a shovel and open a hole about 5-6 inches deep for each corm (Figure 1) and cover it as I open the hole for the next one.  It is also possible to dig a planting trench with a trenching attachment for a rototiller or other power equipment and then lay the corms into the trench to be covered. Make sure each corm is oriented with growth buds up and root zone down.  Smaller corms can be planted shallower and large corms deeper. Deeply anchored corms are less likely to flop over when in bloom. Some growers even hill up the beds as the glads grow to provide more support.

Most cultivars have their own biological clocks as to bloom time and are classified as follows: very early season VE (less than 70 days); early season E (70-74 days); early midseason EM (75-79 days); midseason M (80-84 days); late midseason LM (85-90 days); Late L (91-99 days); and very late VL ( over 100 days). Hence, by either planting a mix of early to late cultivars at one time or a grouping of same season cultivars every 10-14 days or some combination thereof, a steady supply of cut flowers through the season is usually assured once blooming commences (Figure 2).

Figure 1. Planting corms with a shovel.

Figure 2. Two double rows of glads. Both rows have been in the ground 2 years.

Mulching the glads as they come up with hay, straw, leaves or compost will help suppress weeds around the plants. Moist soil is important to get the corms growing and the soil moisture should be maintained until well after blooming is completed to store energy in the new corm for the following year. Glads require at least one inch of water per week. Irrigating can be done by soaker hose or by flood irrigating shallow trenches cut on each side of the bed. Cultivation for weeding should also be shallow to avoid disturbing roots. Hand weeding may be necessary.

 

Cultivars are best planted in groups and labeled with stakes or markers so that later when digging the corms you will be able to keep cultivars segregated by name.

 

Flowers are best harvested when there are only a few buds open at the bottom of the spike and it is best done in early morning. It is important not to cut too deeply into the foliage when harvesting flower spikes because the foliage is needed for photosynthesis to assure a healthy full-sized new corm or corms for the following year. The new corm is not really developed until after the flower is harvested and all the energy of the plant is then devoted to the new corm. A knife with a medium blade length can be slid down the stalk inside the leaves and then turned upward to cut a stalk of proper length without unduly cutting leaves. Shears can be used, but they may crush the stems and cut more leaves than careful knife cutting.  Flowers do best if placed in water immediately. Glad competitions are common at flower shows and fairs (Figure 3). The display is usually of one spike, but others are possible. The reference below covers exhibition growing in detail. For the home display, tall vases or French floral buckets work nicely (Figure 4).

Figure 3.  Gladiolus competition at the San Joaquin County Fair.

 

   

Figure 4.  French floral bucket containing Priscilla gladiolus.