Irises belonging to this group emerge from bulbs whose structure is similar to the vegetable that leads to much misery when they are peeled. In fact, a number of most well known irises, which are very frequently found in florist shops, actually grow out of bulbs. Some such irises include the English, Spanish and Dutch irises, which are tall growing aristocratic varieties having well-formed, rich-hued, yellow and purple-blue blooms. Bulbous irises have some specific characteristics - all of them shed their leaves after the flowering season, they go into a dormant phase during summer, they all can be propagated from their seeds, and they require being lifted once in a while and replanted. Although all bulbous irises can be propagated from their seeds, the plants grown in this way will produce their first flower much later compared to those that are grown by vegetative propagation from the rhizomes. More importantly, true hybrids, which possess the traits of the parent plants, can only be developed from the bulblets that grow from the parent bulb every season. Moreover, this also ensures the increase of the species. Similar to daffodils, bulbous irises' foliage begins to look untidy after the flowering season. When the leaves of these irises begin to wilt, tidy gardeners become eager to get rid of them and start looking for the secateurs. However, this is not advisable, as the bulb is considered to be pregnant during this phase. Therefore, it needs to be taken care of and the leaves of the plant help to provide them with the required nourishments. In fact, the last couple of months of the plant's growth are very important, as this is the time when the development of the buds for the ensuing season takes place. In fact, bulbous irises do not have a preference for heavy clay, but clay soils can be modified to support their growth by adding humus, sand and gravel. If you dig out the bulbs and store them outside, you should ensure that they are kept in a shaded place that is cool and bereft of moisture. At the same time, they require an excellent air circulation.
While purchasing irises in the form of cut flowers, people usually prefer buying English, Dutch or Spanish irises. Nevertheless, these names are often confusing. In fact, the irises that we generally buy as well as cultivate are more often than not hybridized varieties that have been raised from an original collection of irises that comprises eight species and all these iris species have their origin either in Western Europe or in North Africa. What we know is the English irises are actually hybrids that have been obtained from I. latifolia, which is indigenous to the Pyrenees. Similarly, the Spanish irises have their origin in I. xiphium, which is native to countries that are located in the Mediterranean region, counting Spain. On the other hand, the Dutch irises derive their name from the fact that they were developed by Dutch growers in the early 20th century. In fact, these Dutch growers were trying to prolong the flowering season of the Spanish irises by hybridizing them with i. xiphium as well as I. tingitana, which has its origin in Morocco. In the process, the Dutch growers developed irises that were bigger as well as bloomed earlier compared to the true Spanish irises. Interestingly enough, the cultivation of the Dutch irises is so controlled now that growers are able to make them produce flowers at whatever time of the year they wish to. Generally, one iris bulb produces a single flowering stem, which bears two flowers that open one after the other. Dutch irises are in bloom during spring, ahead of the tall bearded irises. Even several Spanish irises flower during this time. It is essential to dig out the Dutch as well as the Spanish irises once in two to three years - at a time when their foliage starts drying. After digging them out, these plants should be kept in a shaded place to allow them to dry. When grown in the northern hemisphere, it is also important to replant them in August - just in time to allow them to grow roots. On the other hand, if you are growing Dutch and Spanish irises in the southern hemisphere, they should ideally be replanted in February. If the bulbs are dug out and left outside the ground, they will eventually lose their vigour and become vulnerable to various diseases. Moreover, the flowers of these plants will also be of an inferior quality. The English, Spanish and Dutch irises have a preference for a soil having good drainage and are reasonably fertile. The plants will thrive better when they are grown in a well prepared soil with a slight top dressing with lime and in a sunlit location. If the soil is infertile, it will result in poor quality flowers. On the other hand, a very fertile soil may promote fungal diseases. The bulbs should be planted at reasonable intervals and to a depth of approximately 4 inches (10 cm). Usually, the xiphium crosses are tall plants and some of them even grow up to a height of about 3 feet (1 meter) or even more. Only propagating these plants from their bulblets will give progenies of true forms. These bulblets appear every season after the flowering season. You will be able to build a good stock very quickly provided you dig out the main bulb every year and detach the bulblets. Excavate the bulbs in the beginning of summer and let them to dry out thoroughly for approximately one month prior to detaching their bulblets. Replant the bulbs in fresh soil at the earliest, because they may possibly be susceptible to mold attack. Planting the bulbs in a humus-rich soil will promote their continuous growth till the very end of the growing season. Various Spanish irises, including a deep purplish-blue variety called "Delft's Blue", and a lighter blue variety named the "Enchantress" as well as the Dutch irises like "Wedgwood", a variety that blooms early in the season, and the "Professor Blaauw", are all rewarding irises for growing in the garden. In addition, these irises are also wonderful when used as cut flowers. While you are cutting the flowers from the plant, ensure that you always leave no less than four leaves for nourishing the bulbs. At the same time, be careful so that you do not damage these leaves with secateurs or knives. All varieties of xiphium irises are also susceptible to viral infections. You can diagnose a viral attack when you see yellowish streaks in the iris leaves, which subsequently start rotting at their base. Iris bulbs that are infected by viruses should be excavated as soon as you notice the problem and burned. In addition, you should also fumigate the ground prior to replanting any new bulb or bulblet.