Gardening Tips: Root Cuttings

Tips for thr propagating of trees, shrubs and perennials from root cuttings which are thick and fleshy and has a high carbohydrate content.

A key factor in taking root cuttings is the time of year that they are taken which is best, in most cases, to be in late winter when most carbohydrate is stored for the Spring growth.

The age and health of the plant is another important factor. Stock plants should be under the age of five. Young roots (preferably 1 year old) should be taken as close to the crown of the plant as possible where the greatset capacity to regenerate resides. By lifting and replanting a stock plant each winter, a permanent system for supplying young roots can be provided, using roots for cuttings and trimming back top growth to keep the shoot:root ratio in proportion. Stock plants will need feeding and irrigating to continue production of usable roots for propagation each year. For very invasive species growing stock plants in containers is a probably good idea,

The roots should be washed free of soil before cutting into lengths. Vigorous hardy plants produce long fleshy roots which can be planted directly (vertically) in the ground in late winter. Such root cuttings need to be 10-15 cm long and at least 5mm in diameter. Regeneration may take 16 weeks in outdoor conditions, but in a protected environment (cold frame, greenhouse, polytunnel), regeneration may take 8 to 10 weeks and the cutting need only be 55-65mm long. If basal heat is used (18C) then the size can be reduced even further, to 25-30mm and the regeneraton time reduced to 4-6 weeks.

Roots which regenerate easily can be cut into suitable lengths and placed horizontally in the growing medium and covered. Hormone rooting compounds are not suitable as they stimulate the roots but curb shoot development.

More difficult subjects respond better if the cuttings are placed with the end of the root nearest the crown which then becomes the top of the cutting. This is easier if, when cut, the cuttings are made with a flat cut on the top end and a slanting cut at the bottom.

A common source of failure is rotting in late winter/early spring, which happens easily if root cuttings are kept damp. Another cause of failure is impatience. Cuttings should only just be moist; only a little watering is required before growth starts. Top growth will start before root growth, so make sure that the roots are growing well before transplanting the cuttings.

The open ground method of propagating involves burying bundles of 10-20 cuttings in an open moist medium. The cuttings are kept at a constant %C for 6/8 weeks under cover in a well ventilated building. After treatment, when the weather conditions are suitable, they can be planted out. This precess reduces the winter survival period of the cuttings and conserves energy for the regeneration process.

The soil should be well cultivated, with good drainage. If cuttings are placed in lines, then trenches can be made which are refilled with a friable soil and sand or a mixture.

Species that are suitable for open ground root cuttings produce long vigorous root systems which can tolerate winter soil conditions.

Poltunnels allow a greater control of growth and improve success dramatically for root cuttings. The soil or compost used should be friable and of good drainage, slightly acid in pH 5.5/6.5 and cuttings placed in rows. The root cuttings can be planted in containers such as pots and trays and placed in frame / tunnel / particularly useful when propergating invasive plants, eg. horseradish, where the smallest piece of root remaining after lifting the cutting may cause a weed problem.

Cuttings are covered with grit, perlite or vermiculite to ensure good aeration.

If basal heat can be applied to polytunnels and greenhouses in addition to the items mentioned above for protected environments than still more species can be propergated. It is important thet the air tempreture be kept as cool as possible but not freezing (about 2C as warm air tempretures can force excessive shoot growth at the expense of root growth. Cuttings can be potted on when they have fully regenerated with the adequate new root : shoot ratio.

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