Iris

Iris02TALL BEARDED IRIS

ASPECT:  Full sun is best, but good bloom can still be obtained with half a day’s sun. The heavier the shade the less likely they are to flower.

CLIMATE:  Best suited to dry summers and cold to frosty winters. If there is not enough cold then flowers are not initiated and blooming will be poor and on very short stems, even to being right down in the fan. (See State by State headings). High summer rainfall can cause problems with rot.

SOIL TYPE: Bearded Iris prefer a neutral to alkaline well-drained soil, but will grow in acidic soils. A friable, well-drained soil with sufficient nutrients to support growth is best.

WHEN TO PLANT: The best time to plant is immediately after flowering. That is November through till after the end of March. Later planting is acceptable, but the later they are planted, the lower percentage of bloom can be expected the following spring. The Iris experts who grow their Iris for showing have their planting completed by Christmas to give maximum growing time to give quality flower stems.

REPLANTING: The optimum length of time can vary according to climate and soil type. On a light sandy soil around Melbourne they are best replanted every year and again the people who show the blooms usually replant every year. In general garden conditions, two years on a light soil and 3 to 4 years on a heavier soil in a cooler climate should suffice for continual good blooming. An idea to assess the plants after two seasons and select those clumps that are really looking crowded, lift and divide them and the following year lift those remaining. This breaks up the work load and it keeps up a full display.

iris1DEPTH OF PLANTING: Rhizomes need to be planted just at soil level. Make a mound of soil in a small hole, sit the rhizome on top of the mound so the roots hang into the hole, then cover the rhizome and roots with soil.

DISTANCE APART: Planting 10-20cms apart will give you an established clump straight away, but planted further apart is also ok.

CUTTING BACK FOLIAGE: Unless replanting, don’t cut back the foliage in summer. This could result in a 15% reduction in flowering the following year. Just pull away dead foliage.

FERTILISERS: At planting time a slow release, all purpose fertiliser is recommended. The important point about both of these is to ensure they are underneath the rhizomes and not scattered around the plants.

A side dressing in early spring of a rose fertiliser will improve flower quality and colour. Don’t overuse animal manure and blood and bone (nitrogenous fertilisers) as this will promote soft growth and in turn rot and leaf spot and also poor flowering. Organic fertilisers are best used in autum.

WATERING: Water in well on planting, then a good soaking once a week is enough. If they are established, once a week over hot dry periods is ample. Over-watering can also cause soft growth prone to disease.

iris2PESTS AND DISEASES:  Fungal leaf spots can occur, especially if it is too wet. You can remove these leaves, ignore them, or spray with a fungicide. If the position is right they are usually fairly disease free.

Over-watering and over-feeding can make the problem worse so we suggest you do not use animal manure on the soil around the plants and water once a week in dry periods. Rhizome rot can sometimes occur, often in the summer when it is hot and humid. This is often due to over-watering when it is too hot. If the plant looks like it can be saved, cut away the infected part and expose to the sun to dry out. Dry tips can occur over summer due to dryness or salty water. Snails can sometimes attack the leaves.

POT CULTURE: Some of the best Iris are grown in pots. Use pots of at least 10″ diameter, preferably larger. Use the best soil mix available and use the same fertilisers as for planting in garden beds. Put the pots where they get at least half day sun and winter cold. They will need to be watered more often.

Flowering time is usually the same as for Tall Bearded grown in the open garden,mid October through to late November.

CUT FLOWERS: Though they are fairly fragile, they can be used as commercial cut flowers if a little care is taken in picking them in bud 2 or 3 days before they would open and wrapping 2 or 3 stems together in tissue paper and either laying the flat for transport or storing them overnight in water in a cool place.


Iris3MEDIAN BEARDED IRIS

These irises grow somewhere in between the Tall and dwarf varieties. Cultural directions are the same as for Tall Bearded Iris, but they do tolerate colder conditions. Median Bearded Iris flower from early October and flow through into the early Tall Bearded season. They are more tolerant of exposed sites due to their smaller size.


DWARF BEARDED IRIS

ASPECT Full sun is essential. Partial sun results in little or no flower.

CLIMATE Some frosty mornings in the winter are essential or there will be a profusion of foliage and no flowers.

SOIL TYPE As long as it affords the plant a good loose root run it does not matter, otherwise it is much the same as for Tall Bearded Iris.

WHEN TO PLANT AND REPLANTING Same as for Tall Bearded types, but in colder climates they may be left in borders for many years with no lessening in bloom. If bloom quantity does diminish, lift and replant after blooming.

iris4DEPTHS OF PLANTING Just cover the rhizome. If too deep it will stop flowering.

DISTANCE APART 25cms to 35cms

FERTILISERS More care should be taken than with Tall Bearded so as not to overproduce foliage with too much nitrogenous manure and too much artificial fertiliser can burn the plants. Fertilise as you would Azaleas. Feed in summer or on replanting and or a light side dressing in August of Azalea food.

WATERING They may require to be watered more often than the Tall Bearded Iris, particularly if planted in light sandy soil that can heat up in summer. Maybe every 4 or 5 days, more often in heat wave conditions. Once established, ease off to once a week.

DISEASES Leaf spot and rust are the main problems. Treat the same as Tall Bearded. Rhizome rot is rarely seen in Dwarf Bearded Iris.

POT CULTURE Dwarf Bearded Iris are particularly well suited to pot culture. Select pots of a diameter of 20 cms or more. If 30cm pots are used, 3 rhizomes can be planted in each to give a massed display. Make sure the pots are in the sun all day and get plenty of winter cold, preferably frost. They may need to be watered more often than the Tall Bearded types, otherwise culture is the same.


 iris5LOUISIANA IRIS

ASPECT Full sun or light shade. Dappled sunlight is fine, but too much shade can prevent good flowering in spring. Plant in partial shade in hot climates.

CLIMATE Louisiana Iris come from the southern states of America where it is hot and humid, so they do well in similar areas of Australia, particularly where Tall Bearded will not thrive. They are excellent in Coastal area of NSW and Queensland. They also give wonderful results in and around Perth. They do well in other areas of Australia but maybe not as well in really cold mountainous areas where severe frost is prevalent.

SOIL TYPE They are very heavy feeders and prefer a good rich loam or soil that has had the addition of plenty of humus and compost. They will not tolerate alkaline or limey soil, so the pH level must be below 6.5. For this reason avoid putting too much fowl manure in the soil.

SUITABILITY TO WATER PLANTING Possibly the best Iris for planting in water or boggy conditions as well as normal garden beds. If they are planted around dams, ensure that the soil is rich and not just subsoil left after the dam was excavated.

If they are to be planted in pots, it is best to establish the plants in the pots for a few months first or they may float out of the pot. 1″ of gravel on the surface of the pot may prevent this.

In selecting a potting mix, make it as rich as possible and be considerate of any fish in the pond as artificial fertiliser may not be suitable.

iris6WHEN TO PLANT The best time for planting is after flowering in December through summer and autumn, but as these Iris are basically evergreen, they can be planted at any time; but we suggest it is best to avoid planting just before bloom time which is in October and November.

REPLANTING The same as for Tall Bearded Iris, 1 to 3 years, but because these Iris can be so vigorous, care has to be taken to see that they don’t get mixed as they can easily grow into each other.

DEPTHS OF PLANTING Louisiana iris tend to send their roots to the surface, so it is best to cover the rhizomes with 2cms to 5cms of soil. Also they would benefit from a light mulch in particularly hot areas. This mulch can be bark, leaves or light compost. Avoid lawn clippings as they can get very hot.

FERTILISERS Use plenty of compost, cow manure, or any other suitable soil improver. Also the addition of a long term slow release fertiliser will improve flower quality. Apply on planting and again a side dressing in September of Azalea and Camellia food will give good results.

WATERING They can’t be over-watered. Also once established they are remarkably drought resistant as long as the weeds are kept out of the clumps.

DISEASES Leaf spot and rust seem to be the main problems and the same conditions and preventative measures apply as do for Tall Bearded Iris. However if a plant variety seems to be a continual problem in a bed, plant it somewhere else, or discard it and grow another variety.

POT CULTURE They may be grown in 25 cms pots for best results. Use the best soil available and treat as for Tall Bearded Iris.

CUT FLOWERS They are suitable as cut flowers.


iris7SPURIA IRIS

ASPECT Must be in full sun or little or no flowers will result.

CLIMATE Hot dry areas with low summer rainfall are best. If there is a lot of summer rainfall, Mustard Seed fungus can cause rot problems. They also require winter cold, preferably some frost.

SOIL TYPE They like a good rich soil with some depth. Good drainage is important but a moist soil, as long as excess water can drain away, is fine. They are fairly tolerant of pH and do well in sandy soil or clay loam.

WHEN TO PLANT The ideal time is late summer and autumn. They resent being moved and often won’t flower very well in the year after moving. They also usually fall if moved too early as the rhizomes have to mature.

REPLANTING Select a place to plant Spurias where they can stay for 4 or more years, as they will give a good show if left in place as long as they have some annual fertiliser program. They don’t mind being a bit crowded.

DEPTH OF PLANTING Cover with at least 5cms of soil. If they are too near the surface they will not take hold as well and will take extra time to become established until they can pull themselves down.

DISTANCE APART 40cms to 60cms

FERTILISERS On planting use pelletised animal manure and/or Osmocote underneath and a side dressing of balanced fertiliser in spring. Summer dressings of old compost or old animal manure can be applied in later years, taking care to keep it away from the plants. Work it gently into the ground. Generally much the same as for Tall Bearded Iris.

WATERING This is quite important. Spurias have a dormant period over summer, and at this stage they should have little or no water until the growth starts again in autumn. So select a place where water can be withdrawn over summer. Rot can easily result if over-watered.

WINTER JOY Because these Iris have a summer dormancy, they start to grow in autumn and have delightful foliage over winter and early spring and look very effective in a garden setting with dark green sword-like foliage.

DISEASES A little leaf spot is noticeable and is rarely a worry.

CUT FLOWERS Possibly the Iris with the most potential as a cut flower. They flower in November when most other Iris have finished. They can have stems up to 4 ft long for large vases and they are not as fragile as other Iris. Pick in bud 1 or 2 days from opening.


SIBERIAN IRIS

ASPECT Full sun. Less sun will result in less flowering.

CLIMATE Areas with cold winters and some hard regular frosts are best. If frosts are not a climatic feature, then flowering could be poor or the flower stems will be very short.

SOIL TYPE They should have rich soil with plenty of moisture and should not be allowed to dry out. They will grow in quite damp conditions, along creeks, besides ponds etc. but not in standing water.

WHEN TO PLANT Siberian Iris are totally dormant in winter, so they can be moved any time after they have matured in later summer through to August. They don’t like moving much and may not flower well in the first year after planting.

REPLANTING Select a place where they will not have to be moved for 4 or more years. They form tight neat clumps and are not invasive. They generally have to be cut up with a knife or treated as a perennial, rather than as an Iris.

DEPTH OF PLANTING Cover just the crown with no more than an inch of soil.

DISTANCE APART 40cms to 60cms

FERTILISERS They are heavy feeders and prefer organic fertilisers over chemical fertilisers. A light dressing of rose food in spring may improve the quality of bloom. They love compost or cow manure.

WATERING Regular watering is important. Don’t let them dry out like Spurias or Tall Bearded. Good soakings once a week, or more often if necessary, particularly if replanted in summer.

DISEASES Virtually disease free.

POT CULTURE They flower in pots if they are 20cms or more in diameter. Use a good soil mix with plenty of organic matter. Don’t let them dry out and ensure they get plenty of sun and winter frost.

CUT FLOWERS They are in many people’s eyes the most graceful of the Iris and are ideal for cutting and taking inside. Each clump flowers profusely once established, so there are usually plenty to cut and leave a display in the garden. They usually flower after the Tall Bearded are past their peak, so continuity of bloom with Siberians ensures a good supply of flowers to cut.


EVANSIAS

CULTURE Evergreen Iris that are suitable for semi-shade or morning sun only. Ideal for light woodland landscaping. Protect from heavy frost of more than -5̊ C. They don’t like lime and are heavy feeders. Use organic material and use it as a mulch. Keep the plants well drained but don’t let them dry out. They don’t have to be replanted very often (except for Iris Tectorum) and they can become invasive, but are easy to remove as they are just in the top couple of inches of soil.

IRIS TECTORUM  It seems to do best if replanted each year. It is excellent in a pot, but again repot each season.

IRIS CRISTATA Another Evansia. This is also best if replanted each season. Also it is totally dormant in winter and as it is such a tiny Iris, it needs to be carefully marked in the garden for winter as it could easily be lost in winter gardening, having such small rhizomes.


JAPANESE IRIS

CULTURE These lovely Iris can be treated in the same way culturally as Siberian Iris with a couple of extra notes.

SOIL TYPE They will not tolerate lime. It will kill them. So make sure the pH is below 6.

SUITABILITY FOR WATER Many publications recommend these Iris for ponds.

They are good in water but precautions have to be taken to ensure they don’t rot in winter. So it is best to remove the pots after the leaves start to brown off in autumn and let the pots be treated as normal pot plants during winter. Repot them at this time and put the pots back into the pond when the leaves start to shoot in September. For quality flowers in pots repot every year.

REPLANTING Japanese Iris are very heavy feeders and we have found that it is best to replant every year or every second year in normal garden beds to keep up the flower quality and quantity.


WINTER IRIS

IRIS UNGUICULARIS (IRIS STYLOSA)

CULTURE Very tough group of Iris that can be planted at most times of the year. Avoid very hot dry weather. They need little or no attention and can be left in the one place for many years. They enjoy dappled light under trees and grow well in large shadehouses. They must have good drainage. Otherwise, please yourself how they are treated. Pots, borders, features for colour in winter, when there is nothing much flowering.

FOLIAGE They have shiny dark green narrow leaves, and as the flowers have no stem the flower display may be enhanced by cutting back the foliage by about a third in April/May.


SIX COMMONLY ASKED QUESTIONS ABOUT BEARDED IRIS

Why won’t my Bearded Iris flower?

Non-bloom of Bearded Iris can be caused by a number of factors and usually it is a combination of several factors.

  • Planting in too much shade. They should have at least half day sun, preferably full sun. The Iris need sun and heat in particular during January and February to form flowers for next spring.
  • Letting weeds, perennials or annuals like Petunias cover the rhizomes. This acts much the same as too much shade.
  • Planting too deep. Rhizomes need to be just at soil level.
  • Over-feeding with too much nitrogenous fertilizer. Nitrogenous fertilizers such as blood and bone or animal manure make leaf growth and Iris are grown for bloom, not foliage. Use a balanced fertilizer on planting such as a rose fertilizer. If soil is really poor you can use pelletised animal or poultry manure on planting but make sure it goes underneath. Do not spread it around the plants as it can cause rot and aggravate leaf spot in summer. Do not use any sort of mulch, this will stop bloom and could also cause rot.
  • Over-watering or under-watering can also cause bloom failure due to not enough water to grow well enough to make bloom size rhizomes and over-watering can cause the roots to rot and the same result will occur. Once established a good deep watering once a week is sufficient, maybe more often in a heat wave, but do it in the cool of the evening.

 When is the best time to replant Bearded Iris and how often should it be done?

  • Immediately after blooming is the best time to replant, that is December. This lets the plants have a full season of growth where they are to flower. Iris are best replanted every 2 to 3 years. Many people replant every year, particularly if they are growing for exhibition at shows. If they are not replanted after 3 years, they become very crowded and flowering quality and quantity decline.

How long can rhizomes of Bearded Iris be left out of the ground?

  • The ideal is to replant immediately upon lifting, however they are very tough plants and can be left out of the ground in a cool and dry place for several weeks without much harm. Do not let them get wet or moist. Keep them dry.

All my Iris have turned out to be white (or blue) and all the pretty pink ones have reverted. Why?

  • This cannot happen. What usually occurs is that the white and blue varieties are usually the strongest and smother the other colours not letting them flower. Keep the colours well marked in some way in the garden and you will always know what varieties you have.

My Iris have brown spots on the leaves. What is it?

This is a fungal disease called leaf spot and usually causes no bother except unsightliness. This can be reduced by clean cultivation, making sure no animal manure or compost or other mulch that can break down is around the base of the plants. If severe a fungicide can used.

Should I cut back the Iris after flowering?

RECOMMENDED PLANTING

T.B.’s Medians Dwarfs Spurias Lousianas Siberians Evansias
Q/land Coastal NO NO NO NO YES NO YES
Q/land Inland e.g. Darling Downs YES YES YES YES YES YES YES
NSW.. North of Newcastle Coastal NO NO NO NO YES NO YES
NSW YES YES YES YES YES YES YES
Victoria YES YES YES YES YES YES YES
Tasmania YES YES YES YES YES YES YES
South Aust. YES YES YES YES Some Areas YES YES
W.A. Perth Area Some Areas Some Areas Some Areas YES YES NO YES
W.A. South & Inland Frosty Areas YES YES YES YES YES YES YES
W.A. Northern Coastal & N.T. NO NO NO NO YES NO YES