STARTING YOUR RHIZOME INTO GROWTH
This section covers plants received as rhizomes via mail order or your own splits. Early or dormant season plantings, January-March will need to be grown on with warmth and light such as on a sunny window sill or in a heated propagator or in a warm room or the rhizome may rot due to the damage done when split from the parent clump. The easiest way is to buy from April onwards when you can plant in a cold greenhouse/polytunnel etc. Getting the rhizome into growth early will result in a bigger plant during the growing season which can be very beneficial in the first season. Planted early in the season one rhizome would typically produce 5-8 stems by the seasons end and will flower in the first year (except musifolia). Canna musifolia bulks up faster than other types I grow but rarely flowers . Unpack your rhizome on receipt and pot on as soon as you can into a pot just large enough, with moist but not wet compost of a type for general use. Initially it doesn't matter what kind, be it bought/homemade or soil based or indeed garden soil. It should be easy to work out what way is up, the rhizome may be just buried or half buried as new roots will form from the underside. Your rhizome may be long like a piece of root with a bud at the end and possibly other developing buds further down. If it is like a bulb I would plant it either just below the surface or with the growing point just protruding. Allow enough space for the growing tip to grow without touching the side of the pot. Adding fertilser at this time may be harmful but if the fertilser is already in the bought compost that's fine. When the rhizome is in growth and you can see some roots you can repot with a little fertiliser or manure added. Manure is most effective at the bottom of the pot. If started early season keep growing in a light and warm environment. If starting the plant in April or later a cool greenhouse is fine if kept frost free.
Sometimes the first leaf of the season may have some brown or transparent patches. The second leaf may also have issues with its appearance on a much lesser scale. This seems to be something to do with the rhizome stopping and then starting into growth again but only in some cases. This issue when it occurs grows out quickly. Also the young leaves are vunerable to minor scorch and burn from being on the windowsill in direct very strong sunlight. When the plant has a few leaves these early ones, if too unsightly, can be removed.
Buying your canna plant with roots and leaves bare root or potted from late April onwards will be more expensive than buying fresh early season rhizomes. Typically the cost of a small growing plant will be around £9. Larger plants may be made available. Stock may fluctuate on availability throughout the summer unless stated sold out for 2021. So check the specific page for the item you are interested in for the latest on availability.
GROWING ON/PLANTING OUT
Once your plant is growing strongly you can feed regularly or pot on with manure or both. Canna are very greedy plants and once growing strongly cannot be overfed or over watered but this doesn't mean keep the pot standing in water as it is best to be able to drain to avoid stagnation of the soil. In the early stages you need to take care but they are easy plants to grow. There is no point planting out too early and the warmer they are kept in the spring the faster they will grow. I aim to plant out here at the end of May. Young plants will be easily killed or badly damaged by late spring frost. Plants can grow strongly in a small pot and they will distort a plastic one if not potted on. Warmth, food and water are the key to large plants. If keeping in pots best results will be obtained in a pot size of at least 30 litres for the final container for all the large types. I grow in the soil and in pots. Potted specimens are great for moving around and providing interest/ adding drama in dull areas throughout the season. Lots of manure used for all the canna's. Unusually you can use fresh horse manure for growing canna's and that is what I use as it is easy to get hold of.
Plant in full sun or dappled shade. Flowering is affected in shade unless growing very vigorously. For foliage they can be grown in shade but as mentioned they thrive on warmth. It is said that darker foliage types loose leaf colour in full sun but I haven't found it so. Flowers can fade in strong sunshine. Canna do not do well in a windy location as the leaves shred and look tatty.
Planted with manure around 50/50 in pots I still feed with vitax Q4 every six weeks or so. This much manure will last the plants at least a couple of years. Those in the ground like plenty of manure added around and in the planting hole. Water frequently for best growth however they are drought tolerant. When anticipating flowers, as a general rule after seven leaves on a stem a flower spike should be visible. Dead heading can be done by shaking the flower stem if they are too tall to pick off. The flowering stem normally branches to produce more flowers so avoid dead heading by cutting down the stem. When the stem has absolutely finished flowering I cut it off above the top leaf, as I grow for foliage as well as flowers. Flowering can go on into early November here.
The general advice is to cut down the stems to the ground after the first frost blackens the leaves and dig them up and keep them as intact as possible, storing frost free and damp with or without light through the winter. Pots, bring in and store the same or dig out the plants from pots too large to move dig out trying to keep the clumps as intact as possible and again store the same. Light and warmth to bring into growth in the Spring, this is the best time to split them. However here I mulch the plants or cover the pots and leave in situ and for frosts down to -3c this works for me. Some damage may occur but the plants survive. Canna musifolia seems, from my observations, to be hardier than the others I grow and sustains less damage. Levels of frost vary with a more penetrating wind frost able to cause more damage. A deep mulch and plastic sheeting can help. Deep snow before the frost gets severe is helpful too. For pots try and store out of the chilled winds and wrap the pots in polythene or pond liner. Winter 2019 the canna's remained in situ throughout. I watch the weather forecasts and bring in if -3c or colder is expected. Canna left outside are slow into growth initially due to the cooler temperatures experienced compared to those brought in. They catch up eventually but you get a longer season from those brought in and grown in the greenhouse during the spring.
PROBLEMS AND PESTS
Canna are pretty robust, tough, plants with few issues.
The most common problem I hear about is canna's not flowering. This is almost always due to insufficent feeding of the plants.
Pest issues I have experienced are with aphids in the early part of the season but never to serious levels. Spider mite are often a problem especially under glass/polythene and in our warming climate these pests can be an issue in the garden. I always use the recommended biological control and never pesticides.
Canna virus has been a major problem especially affecting dry rhizomes supplied by bulb traders/garden centres and the plants produced from them. It's best to avoid buying the dry rhizomes/bulbs, although of course some people have had success with them. My canna are not produced in this way and I take great care in sourcing my starter stock. All my canna are grown from scratch on site and are healthy. Signs of virus vary as there are many different ones but mottling, yellowing, distortion are all possible signs, browning and rotting during the growing season are signs of some of the more devasting viruses but can also be down to waterlogging in oxygen starved substrate. An extreme example of this would be growing in a bucket of mud with no drainage holes exposed to the heat of the sun. Suspect plants should be isolated or destroyed. That said if plants are grown stressed they may show some erratic leaf growth through rapid temperature fluctuations and yellow patches can be down to a patch of chalk in the soil or some other soil contaminent and things like that. Browning or crisping of the leaf edge can be down to wind burn. When I get a new variety I have always bought only one plant of each variety and they have all been from the national collection. Even then I have burnt a couple on unpacking that may have been virus free but I thought might have the virus. Any new plant coming in is grown in isolation in pots so as not to contaminate my soil and monitored closely for the first year.