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FREQUENTLY ASKED QUESTIONSIRISES AND DAYLILIES
IRISES
MY IRISES HAVEN'T BLOOMED, WHY? 1 - Summer Sun. Irises require full sun for at least half a day in summer. Insufficient summer sun does not allow proper development of flowering. Full sun all day is desirable for most, however dark colored blooms that flower later in the season will last better if given some protection from the hot afternoon sun. Full winter shade is not a problem. Even if your irises are in full sun, the rhizomes may be shaded by mulch or creeping perennials such as violets or evening primrose. Ensure that the soil over the rhizomes is not shaded. 2 - Winter Chill. Just as they like good summer heat, so they like to be chilled in winter. The degree of chilling required depends on the cultivar, but many Dwarf Bearded require actual frosts to bloom. Reblooming irises may need less chilling than other varieties. Some people report good success in inducing dwarf iris to bloom by putting ice on top of the plants a number of times over winter. If you live near the waterfront in Adelaide it may not be cold enough, similarly the western suburbs of Perth and eastern suburbs of Sydney. Most of Brisbane would not receive enough winter chill. Also be aware that if they are against a north facing wall, the wall may retain enough heat at night to prevent sufficient chilling. 3 - Too Much Nitrogen. Excessive use of nitrogen rich fertilizer can cause lush plants with little or no flowers. Bearded irises like good supplies of phosphorous and potassium, and less nitrogen. We recommend pelletised organic fertilizers such as Rapid Raise or Dynamic Lifter. Alternatively use slow release such Osmocote. 4 - Needs Dividing. Irises can exhaust the soil after a number of years, or grow too dense. Depending on the cultivar they will dividing every 2-5 years. They should be moved to another spot or else have their soil refreshed. 5 - Settling In. Sometimes when you buy a plant it may not flower the following spring, but rather will concentrate on establishing itself and then will flower the second spring. 6 - Mild Rot. The part of the rhizome most susceptible to rot is the top of the rhizome where the flowering fan is. Sometimes this may rot a little over winter and the rest of the rhizome survives and the newer small fans along the sides continue to grow, but the fan that would have produced bloom has died. This usually causes reduced bloom rather than total lack of bloom. SPURIA IRIS 1 - Recently Moved. Spuria irises don't like being moved and usually will not bloom the following year. Occasionally it will take 2 years to get bloom. 2- Lack of Summer Sun. Spurias like full summer sun. SIBERIAN IRIS and JAPANESE IRIS 1 - Winter Chill and Summer Sun required. requirements are as for tall bearded irises, except Siberian prefer actual frosts.
WHEN SHOULD I DIVIDE MY IRISES? The best time for Bearded Iris and Louisiana Iris is generally immediately after flowering or in late autumn - early winter. If it is too close to flowering time, bloom will be small, late or not happen at all, but won't damage the plant. Moving during summer is OK, but bearded iris don't grow much over summer so don't water them a lot to get them to grow, you will only induce rot. Irises that go dormant (Siberian, Spuria and Japanese and bulbs) are best moved during dormancy. Spuria iris can be moved soon after they begin their spring growth, but should be planted immediately and not allowed to dry out. Pacific Coast Iris are fussy about when they should be moved. They should only be moved once they have started their winter growth, usually 4-6 weeks after the beginning of the autumn rains i.e. mid May - mid June. Most species (iris I Ungicularis etc) should be moved in autumn with the rains.
HOW DEEP SHOULD I PLANT MY IRISES? Bearded iris should be fairly shallowly planted, with about 1-2 cm (half inch) of soil over the rhizome. Too deep and they won't get enough summer heat or winter chill. If exposed to the sun they may develop scorch in the Australian climate. (Books that talk about exposing the rhizome are generally written for cooler climates where every effort is required for sufficient summer heat). When replanting ensure that the bottom of the rhizome makes good contact with the soil underneath it. Other (beardless) iris should be planted a bit more deeply, 2-4cm. If your Louisiana iris rhizomes end up above the surface of the soil, it doesn't really matter.
Irises need only to be trimmed when moved. The leaves are cut back because the roots have been cut. There is no need to trim any other time, simply remove old, spent leaves.
MY IRISES ROTTED, WHAT HAPPENED? Bearded Iris are more easily killed by over-caring than anything else. Excessive moisture, especially over summer will induce rot. Make sure your bearded iris are well drained. Do not cover the rhizomes with moisture holding mulch (e.g. lawn clippings, pea straw), particularly if you use overhead watering. If rot starts to happen, remove the rotten part of the rhizome and expose the cut surface to the sun for a few days, then replant. Excessive use of nitrogen fertilizer can produce lush plants susceptible to rot. Spuria iris don't like summer humidity, so don't cover with damp mulch in summer. Some parts of Australia e.g. Coastal Sydney and north where there is very high summer humidity may not be suitable at all.
HOW MUCH SHOULD I WATER MY IRIS? Bearded Iris - once every week or two over summer will be fine. Once a clump is established, many will survive without any summer watering. In a dry spring some watering to keep the soil slightly damp may be required. You may put mulch over the roots, but not over the rhizome. When transplanting in summer, water once or twice a week for the first few weeks then no more than once a week. If your irises go completely dormant from lack of water over summer, don't worry they will start growing again in autumn, as long as the rhizome is still fairly firm. In pots water them 2-3 times a week in very dry weather. Spuria Iris - Should not be completely dried out until flowering has finished. Once flowering has finished, if not watered they will die down, go dormant and then come away again with the winter rains. If watered every week or two through summer they will remain green until about April when they will briefly die down , then start their winter growth. Louisiana Iris are swamp irises so need plenty of moisture during winter-spring. They can be mulched fairly heavily. If growing in pots immerse the pots about 2/3 in water but not completely. They can survive reasonable summer dryness but are best kept moist all year round. If they do dry out, rehydrate slowly rather than suddenly soaking in water. Siberian Iris are bog irises and like good winter and summer moisture. Once they go dormant in late summer, they can dry off somewhat. It's OK to mulch them heavily. Pacific Coast Iris like good moisture in winter and spring but not boggy. In summer occasional watering is best, but some seem to be happy with complete summer neglect. Japanese Iris like relative dryness during winter when dormant and plenty of moisture during the growing period over spring and summer. If growing in pots in a pond remove from the pond during winter.
MY FLOWERS ARE DEFORMED, WHAT HAPPENED? Frost Damage - Frost on blooms are out will cause the flowers to go a bit transparent and mushy. Buds that are fully formed will also be damaged by heavy frost. The edges will be slightly curled, ruffling will be lost and plicata colouring will speckled. Damage may persist for several weeks after the frost. Some cultivars will be damaged more than others and it will worse in the more exposed, lower parts of the garden.
Frost Damage Weed killer Damage - Glyphosate type sprays (eg Roundup) used within a couple of months of flowering will damage the blooms. If slight traces have drifted onto the plant the blooms will be whitish around the edges and some ruffling lost. Heavier exposure will lead to completely deformed blooms. Slight exposure to glyphosate will not normally kill your irises but newly transplanted ones will be more susceptible.
Mild Glyphosate Damage More Severe Glyphosate Damage - Dutch Iris
Very Severe Glyphosate Damage - Tall Bearded Iris
MY BEARDED IRISES HAVE TURNED WHITE There are no proven cases of irises actually turning white, however there are several reasons why your patch may end up being all white. Firstly - glyphosate damage -see above. Secondly the patch has been taken over by a white one. Some white cultivars are extremely vigorous and will overgrow less vigorous cultivars. There may have just been a small piece left from previously or else occasionally nurseries make mistakes and a piece of white was mixed in with what you bought. It didn't flower for several years but multiplied rapidly. Then by the time it bloomed it had taken over most/all of the patch of irises.
THE FLOWER STEMS WITHER IN THE MIDDLE AND FALL OVER. This usually happens as a result of weather damage. If the withering is mid- stem it is caused by wind and sudden weather change drying out the stem during a period of very fast growth. Some cultivars will be more susceptible than others.
Withered Stem If the stems falls over at a junction in the stem and is brownish and mushy, water has been trapped in the little leaf at the junction and rot has followed. Usually happens in very wet springs, especially if warm also. CROOKED STEMS If there is steady wind while the flower stems are growing quickly they will tend to grow almost sideways and the straighten once the wind stops. Louisiana stems are naturally a bit snake-like. Very mild silver speckling is caused by hail. Not a problem in itself but it does seem to make the plant more susceptible to fungal leaf spot.
Hail - left Fungal Leaf Spot - right Fungal Leaf Spot Fungal leaf spot is brownish circles over the leaves. Some people just ignore it, if severe you can spray with fungicide. Because most irises have waxy leaves a systemic fungicide may be best as complete coverage would not be required, however they are toxic. See your garden centre for advice. Brown Tips happen over summer. Usually caused by dryness and/or salt accumulation from salty water (e.g. bore) You can trim it off if it bothers you. Snail damage is sometimes caused by tiny white snails, producing torn looking leaves. Some cultivars seem to have less waxy coating and are more susceptible.
Pineappling (photo courtesy of John Jones) Pineappling - is when the leaves grow short, tight and sort of scrunched. It is caused by climate change, often worse on new stock or when the weather is very changeable. Will come right in time.
WHAT SHOULD I FERTILIZE WITH, AND WHEN? We recommend generally fertilizing with Rapid Raiser, Dynamic Lifter or Osmocote. When planting out your irises you can use Seamungus (Neutrog) to aid root development and also for an extra flowering boost use Sudden Impact For Roses (Neutrog) in July-August. However irises that like very acid soil (Louisiana, PCs and Japanese) are best fertilized with aged cow manure (the most acid animal manure) or azalea and camellia fertilizer. It is best to fertilize when transplanting and then at the beginning of the growth period, a couple of months before flowering. WHAT SORT OF SOIL AND CLIMATE DO IRISES LIKE? Bearded Iris and Spuria - neutral to alkaline soil is best, needs to be well drained. If extremely acid may benefit from a little lime. Best suited to climates with relatively dry summers and cool to cold winters. Louisiana - need damp - wet acid soil. If your soil is neutral or alkaline then plant in very large pots with a mix of old cow manure and acidic potting mix. Immerse pots two thirds in water. So long as adequate summer moisture is provided, climate is not a problem. One of the few irises to do well in tropical areas. Will grow OK in cold areas, but if exposed to cold winds during spring the flower stems may be shorter than usual. Siberian Iris - need damp- boggy soil, preferably fairly neutral. They need frosty winters to flower properly. Pacific Coast Iris - need acid soil. Better in areas with relatively dry summers and cool damp winters. Do well in large pots of acidic soil. Japanese Iris - need acid soil. Should not to be immersed in water through winter and need good summer moisture. Need some winter cooling.
HOW LONG CAN MY IRISES STAY OUT OF THE GROUND? Bearded irises can survive out of the ground for several months, if stored in a cool spot. Soak for an a couple of hours before planting. Others are best replanted as soon as possible, although they will survive a while if kept cool and damp. Louisiana irises can be stored in shallow water for a few weeks.
DAYLILIESWHAT ARE THE SMALL INSECTS ON MY PLANTS Daylilies, if stressed, are subject to aphid attack. These are small greenish insects. Spray with an insecticide if severe. Ensure your plants are well fed and watered. Small silver spotting can be hail damage or else damage by spider mites, almost invisible little mites. They can be controlled by a suitable miticide- see your garden centre.
YELLOW BROWN STREAKS AND SPOTS Mild yellow-brown streaking is caused by leaf streak and is not a major problem. There is a new disease in a few parts Australia called Daylily Rust. Excellent information and photos can be found on the sites http://www.ncf.ca/~ah748/rust.html and http://www.dpi.qld.gov.au/health/8060.html . With rust, the leaves, especially the backs, will have reddish spores which will rub off onto a tissue. It spreads very quickly and may spread by wind from nearby gardens and cause considerable damage. If you think you have it, please contact your State Dept of Primary Industries. To limit it's spread , please be careful who you buy/accept plants from and don't take possibly infected plant material to another garden for identification.
Leaf Streak Distorted Leaves - Occasionally in spring the leaves may be slightly distorted, this is just climatic and they will come right as the season progresses
WHAT SORT OF SOIL AND CLIMATE DO DAYLILIES PREFER? We sometimes say that daylilies just need dirt and a water. They are very hardy. However they prefer a fairly sunny spot and appreciate good soil. They are fairly drought resistant but will give much better results if regularly fertilized and watered. They appreciate being mulched. Dormant daylilies will loose all the their leaves in winter and have been bred to survive very cold snowy winters. However most daylilies will grow anywhere in Australia. They also appreciate being well fed. Fed with Rapid Raiser, Dynamic Lifter or Osmocote once or twice a year.
WHEN AND HOW SHOULD I DIVIDE AND HOW DO I PLANT THEM? Daylilies are best divided every 3-5 years. If left any longer they will become very difficult to divide and flower size will be reduced. The best time in Australia is late autumn or early spring. It is best to dig the whole clump with a garden fork, and break into groups of 2-3 fans. Often they will separate themselves, otherwise use a sharp knife. Trim back the foliage. Plant in new spot or refresh the soil where they have been. Add fertilizer (Rapid Raiser or Dynamic Lifter is good). Plant 3-5 cm ( a couple of inches) deep and ensure there is good contact with the soil underneath. If a large air pocket is left underneath the plant may rot and die.
Daylilies perform better with reasonable moisture and don't tend to rot. If well mulched, a good soaking once a week should be sufficient in hot dry weather. Once established, they are fairly drought tolerant but won't flower much if unwatered.
WHAT IS MEANT BY DORMANT, SEMI-EVERGREEN AND EVERGREEN? Evergreen daylilies keep their foliage all year round, there will be some natural turnover of leaves and it is a good idea to remove any dead leaves a couple of times a year. Semi-evergreen daylilies will loose some leaves in winter but not die down completely, so you can always see where they are. The degree of leaf lose will vary with the cultivar and climate. It often will be barely noticeable. Dormant daylilies will loose all their leaves in late autumn and then come away with lovely fresh foliage in spring.
WHAT IS MEANT BY THE TERM RECURRENT? Daylilies produce scapes of bloom in spring and then have a break and then bloom again, just like roses do. Many modern daylilies are strongly recurrent and may have up to 5 rounds of flowering in a season. Older varieties may have less, a few flower only once a year. Dormants tend to be less recurrent but are bred to produce more blooms per scape when they do flower.
WHAT IS MEANT BY TETRAPLOID AND DIPLOID? Originally daylilies had only one pair of chromosomes (Diploid) but some were then bred with a double set of chromosomes (Tetraploid) to give improved substance. However many of the newer diploids are as good, if not better, than some tetraploids. Fancy edges occur only on tetraploids, but many diploids have a delicacy of colouring and form not found on tetraploids. If you are interested in hybridizing you cannot cross diploids with tetraploids. DO I NEED TO SPRAY MY DAYLILIES? Generally daylilies are trouble free and do not needing spraying. They may get aphid problems, particularly if stressed. Some people hose off with water. Organic contact sprays of pyrethrum, garlic and chilli are preferred by some. (Take great care to protect your skin and eyes if using chilli.) Using a systemic poison means you will kill only insects that are eating your plant and you will need to spray less often, but they are toxic. See your garden centre for advice. If tiny mites are a problem, you will need a specific miticide, see your garden centre for advice. If you are unfortunate to develop Daylily Rust, you will need to spray with a systemic fungicide. Ask your agricultural inspector for advice or see the above web sites.
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