The answer is both! Dependant on the variety. Very generally speaking, rhizome type iris produce larger flowers, including bearded type flowers, while bulb type iris produce smaller flowers which are suited to rock gardens or the front of borders to provide early colour in the year.
Specie Iris provide some of the earliest blooms in the garden and are grown from bulbs planted during the Autumn. Bulbs are characterised by thick underground storage organs that contain all the nutrients necessary for the flowering period and re-growth in the next season.
Planting Iris Bulbs
Planting depth and spacing varies depending on the type of Iris being grown, but all should be planted at least three inches (10cm) deep. For best results, water regularly and fertilize every few weeks during the flowering period. With proper planting and care, iris plants will bloom year after year with minimal effort.
Dwarf varieties such as specie Iris Reticulata are particularly happy grown in pots or tubs to pop by the door and catch your attention early spring, maybe partnered with some delicate Narcissus Tete a Tete or Jetfire. There stems are shorter than those of Dutch Iris which flower later during the summer months to compliment borders with eye catching fireworks of colour.
When purchasing iris bulbs, corms or tubers, make sure they are healthy and free from disease by examining them closely before planting.
Rhizomes are specialized shoots, located just below the soil surface, which grow and spread through different areas of the garden.
Planting Iris Rhizomes
Bearded Iris are grown from rhizomes, they should be planted into moist well drained soil at least 6″ (15cm) apart. If necessary add some grit to the existing soil to provide drainage. The reason for planting just below the soil surface is to allow the rhizome to see the sun which they love for healthy growth and good flowering. Using divisions from established clumps or buying bare-root rhizomes will give you quick, reliable results. To keep heights manageable, they can be cut back to ground level in early spring or divided every few years as they will quickly outgrow their space and become overcrowded. Watering regularly during dry spells is essential for a healthy plant and a spectacular display.
Either bulbs or rhizomes can be used to grow beautiful Iris in the garden, and with proper planting and care you’ll enjoy the colourful blooms from early spring right through until late Autumn. Whether it’s Specie Iris for your pots or Flag Iris in a border, there’s something to suit every situation.
Iris Sable, a Bearded Iris, an example of an iris grown from a rhizome.