September 2014 | The Garden 6160 The Garden | September 2014

Planting techniques

Planting techniquesFor plants that will be in the ground for many years, it is worth taking time to plant

them well so that they establish quickly and are then able to thrive

Shrubs and rosesFrom forming the backbone of garden beds to focal points and long-term features, shrubs and roses require particular care.

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As gardeners we want our plants to establish well so that we can enjoy them for many years to come. Plants may be often viewed as an investment because of the cost and time involved – especially with trees and shrubs – so by following some basic principles and advice, and by taking a little extra time, you can give them the best possible start in life.

Planting correctly in the first place is an important step in this journey: as with most things you need to start from the bottom up, and for a plant this means its roots. Primarily for searching out nutrients and water that the plant relies on, roots are equally as valuable for creating firm anchorage into the ground.

A current school of thought is that improving the

soil with organic matter around a plant is more beneficial than just concentrating on the planting hole. Working the soil over a wider area will help with long-term establishment. Improving just the soil in the planting hole can lead to problems; adding organic matter to the planting hole can cause the plant to sink as the organic material breaks down, adversely affecting the plant’s health. The plant may also become too comfortable and not push out and develop all-important anchor roots. Therefore, backfilling the hole with the same material that was dug out will help to promote wider root growth and reach. Fertiliser such as bonemeal, traditionally added to the planting hole, does not appear to greatly boost root establishment.

Time and care spent when planting will be rewarded in the long run.

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Author: Jon Webster, Curator, RHS Garden Rosemoor. Photography: Tim Sandall

Long-term success with climbersMainly shrubby, these plants are often planted in demanding situations so have specific considerations.

Climbers tend to be tough plants and they are usually grown in challenging positions, such as a dry, warm south-facing wall (for Trachelospermum jasminoides) to a cold, dark north wall (enjoyed by Hydrangea anomala subsp. petiolaris). In addition, climbers can face competition from surrounding plants for light and moisture.

Selecting a plant for the right conditions is key and making sure it is cared for (until it establishes – with water, mulch and tying in) is a must. Plant 30–45cm (12–18in) from the wall or fence, or at the edge of the tree canopy, as this allows the plant to keep out of the rain shadow and enables the roots to capitalise on available moisture.

When building a support, allow a gap of at least 5cm (2in) between this and the wall to help the climber attach and grow; this also allows air to circulate around the plant.

Climbers and treesWhen growing a climber up a tree, plant away from the trunk at the canopy edge so the roots will receive more rainfall.

Time of yearThe general rule is to plant deciduous plants during their dormant season (November to March). Plant evergreens in spring or at the end of summer so they have time to settle in before weather extremes, such as drought or drying winds, can cause harm to the foliage.

PlantingDig a hole no deeper than the rootball and up to three times its width. For roses, ensure the graft union is at soil level otherwise the risk of rose die-back is increased. Aftercare is simple: water regularly, mulch, weed and feed until the plant becomes established.

Bare root or container?Bare-root plants tend to be limited to roses, hedging and native plants; these are usually cheaper but the planting season is restricted to winter. Container-grown plants cover a wider range and can be planted at any time of year (but at a higher cost).

TransplantingUsing a spade, cut around the plant roots the year before it is removed to stimulate fibrous root growth and help establishment once moved. Reduce the size of the plant by pruning the top growth; treat the plant as if newly planted, with the appropriate watering and aftercare.

ClematisPlant large-flowered cultivars with their rootball 5–8cm (2–3in) below the soil; evergreen clematis at soil level.

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September 2014 | The Garden 6362 The Garden | September 2014

Planting techniques

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TreesWhether ornamental or productive, all trees benefit greatly from thorough preparation before planting, followed by regular attention.

Ongoing careApply a layer of organic mulch 5–10cm (2–4in) thick around the tree after planting; keep a collar free around the stem of about 10cm (4in) to prevent the bark rotting. The mulch will help to reduce weed competition and also conserve moisture levels in the soil. Check the stake and tree tie each year, and loosen the tie as required. Once the tree is well anchored this can be removed. An annual spring feed using a balanced fertiliser is ideal.

Shape of hole Dig a round hole (below) on lighter soils; on heavier soils it is better to dig a square hole. Roots can find corners to break out in square holes, but in clay can girdle in a round hole. Make the hole three times the width of the roots and spike the sides and bottom with a fork to encourage good drainage.

Time of year to plantAlthough a containerised tree can be planted at any time of year, traditionally trees are planted during their dormant season between November and March.

Bare-root trees are only available from November to March and are cost effective; most fruit trees are produced this way. They need more support, as they have a less-dense root system than containerised plants.

When buying a pot-grown tree make sure it is a healthy plant which has not been sitting around for too long – tell-tale signs include broken pots, moss on the compost and roots coming out of the base. When planting, break the encircling roots as these can cause problems in establishment. Instead of teasing roots out, actually slit the edges of the rootball with your spade – but be gentle with plants with delicate roots that need to be teased (not cut), such as Japanese maples and magnolias. This problem is eliminated in trees grown in Air-Pots; fibrous root growth is promoted by the corrugated walls of the container, and the amount of air holes that allow for efficient drainage and aeration.

Bare root They establish quickly and easily, due to being field grown. Although low cost they have a short planting season and a limited selection is available.

Air-Pot This design encourages fibrous roots to develop. As a result there are no root girdling problems often encountered with mature plants in pots.

Containerised hessian wrapped Used for large semi-mature trees ready for planting or for field-grown shrubs and conifers, lifted during the dormant season.

Containerised in bags Used to grow trees of all types as an alternative method to pots. The added bonus is you can plant them at any time of year.

Planting and aftercareFor an effective hedge, plant in a staggered, double row, spacing young plants 30cm (12in) apart. Stake larger evergreen plants. In spring, cut back top growth to encourage a thicker base.

Types of hedgingA wide palette of plants can be grown as hedges – ranging from formal evergreen yew (often sold in containers) to informal native plantings such as hawthorn and holly, often available as bare-root whips (above).

Irrigation Newly planted trees will require regular watering in spring and summer for the first two to three years after planting, until the tree is fully established. This will help to promote good root growth.

Creating a ‘dish’ of soil at the base of the tree will help when watering and stop it running off. Alternatively, for larger plants, ensure that the water penetrates the soil by placing a perforated drainage pipe around the rootball during planting to be certain that water is delivered directly to the roots.

Correct level and stakingPosition the tree so the top of the roots is just below the soil surface. If the tree is container-ised, scrape away the top level of compost to find this level, and check the depth again prior to backfilling. Staking is key in the early stages until the roots establish, so support the tree trunk to around a third of its height. This will allow the top of the tree to move, which helps stimulate anchor roots to take hold.

Hedging choicesHedges create structure, garden rooms, wildlife habitats or windbreaks, as well as adding privacy and security to our houses and gardens.

Slit or trench plantingSlit planting with a spade is effective for young bare-root plants in cultivated soil. But if you need to prepare the soil for pot-grown plants, create a trench, place the plants in and backfill accordingly.

Mound the soil to create a dish that will retain water close to the tree roots.

Roots are more likely to grow out into the corners of square planting holes.

Mulch after planting with organic matter but keep it

clear of the tree trunk.

Firm the soil in the hole after planting and staking.

Transplanting mature trees: a case studyMalus ‘Zabergau Reinette’ had been growing in the fruit nursery at RHS Garden Wisley, Surrey in an old wooden apple crate for many years, so it was ready to be planted out. First, a large, square hole was dug to accommodate the rootball; once the tree was moved to the hole, the crate was broken off (inset) to reveal the root structure was in a good state. The old soil was removed and, once the best ‘face’ of the tree was chosen, the apple was carefully lowered in. Due to the sandy soil and mature state of the tree, the hole was backfilled with compacted layers of soil and organic matter in order to help it establish. Finally, a strong stake was used and the tree watered regularly until it established.

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64 The Garden | September 2014

Perennials Pot-grown plants 1 can be planted throughout the year, but this is best done during autumn and spring when the soil has some warmth. When planting in summer, ‘puddle in’ plants by filling the hole with water 2 before backfilling.

Perennials enjoy a rich soil; beds can be prepared with well-rotted manure or compost to improve the structure and fertility.

Annuals These give seasonal, colourful displays and prefer a well-cultivated soil 3 . However, be sure it is not too rich as they can put on lush growth and at the expense of its flowers. Ensure they are watered well in dry weather after planting.

Bulbs Dormant bulbs should be planted between September and November while the soil still has some warmth, but a few, such as snowdrops and bluebells, are available after they have flowered, for planting during summer. A general rule for bulbs is to plant them to a depth of three times their size 4 to provide good anchorage and to prevent drying out.

Find out more✤ Search ‘Planting’ at www.rhs.org.uk/advice

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Perennials, annuals and bulbsEven small plants need some care when they are planted if they are to perform well over time.

Planting and mycorrhizaeThere are products on the market that contain mycorrhizal fungi, which can be applied to the roots at the time of planting and can help with establishment of plants in certain situations – but there are factors that need to be taken into consideration. See The Garden, August, pp46–48 for the latest thinking.

Trees can take a long time to grow to create the impact within our gardens or landscape that we desire. However, there are several companies specialising in the supply and planting of what are called semi-mature trees (as used to bulk up the woodland planting by the lake at RHS Garden Hyde Hall in Essex, below).

To ensure success, check the provenance of the tree; particularly where it was grown so the climate and soil type can be compared with those where it is to be planted. If the tree is from a nursery specialising in mature stock it should have undergone regular root pruning to promote a fibrous root system to allow it to be planted at any time of year.

Even though they are mature trees, the plants still require a lot of care in the early years, and can take longer to establish in new surroundings than smaller trees; as always, watering, mulching and correct staking are key to success.

Instant trees

The trees are planted as delivered and roots grow unhindered through the hessian as it rots.

Planting semi-mature Betula supplied by Majestic Trees at RHS Garden Hyde Hall requires special handling, but gives instant impact.

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