7 Step Step-Over Apple Cordon Training with Cox on M27 Rootstock

Why M27 changes the scale

M27 is the weakest of the Malling apple rootstocks. It was raised at East Malling Research in Kent and released for commercial use in the 1970s. On a free-standing form, a tree on M27 usually reaches about 1.2 to 1.8 m and makes only a fraction of the root vigour found in M26 or MM106.

That weakness suits a step-over cordon. The arm is carried at 40 to 45 cm above the ground, so a vigorous stock would keep trying to throw strong upright growth from the bend and the top of the arm. M27 gives a calmer framework. It accepts the horizontal training more readily and keeps the whole tree below knee height for its life.

The price of that smallness is permanent support. M27 has a brittle, shallow root plate and cannot anchor itself securely. The Royal Horticultural Society lists M27 as needing staking for life; MM106 commonly suits staking for the first three years. In a step-over, the permanent support is usually a low wire.

Feeding also matters more on this stock. A small root system cannot scavenge poor soil effectively, so the nutrients have to be placed within reach. Cox Orange Pippin adds another constraint. It is a triploid-adjacent, disease-prone variety with modest natural vigour, which places Cox on M27 at the low end of the growth scale.

Steps 1 and 2: posts, wire and the right maiden

Set two posts 1.5 to 1.8 m apart, leaving 45 cm of post above soil level. Run one galvanised wire, 12 to 14 gauge, between the posts and tighten it with a straining bolt. The wire must stay firm under the weight of a fruiting arm, because a sagging line distorts the bend and lifts the tip.

For a row of step-overs used as edging, repeat the post-and-wire run end to end. Tension each span separately so one loose section does not affect the whole row.

Plant during the dormant season, from November to March. Use a maiden whip, meaning a one-year-old unbranched tree. Keep the graft union 10 to 15 cm above the soil so the Cox scion cannot root above the M27 union and bypass the dwarfing effect.

Firm the soil around the roots, then tie the young stem loosely to a vertical cane for the first few weeks. A feathered maiden already carries side shoots and is more awkward to train flat. A clean whip is worth finding from a specialist nursery such as Blackmoor or Keepers Nursery.

Step 3: making the bend

This is the operation most likely to spoil the shape. Let the maiden settle after planting, then make the bend during spring sap rise, when the stem has more give. Bring the single stem down in one slow movement until the tip meets the wire, then tie it along the wire at three or four points with soft string. Wire ties can bite into bark as the stem thickens.

If the stem is pulled below the horizontal, buds along the length may sit idle and fail to push. Leaving the arm above level creates a different problem, because the highest point tends to dominate and send up a strong vertical shoot while the rest of the arm stays weak. The target is a clean 90-degree turn from the short upright leg, followed by a flat run along the wire.

M27 helps here because it does not surge after the bend. When a maiden is too stiff to bend safely in one season, leave it upright for a year, allow it to thicken, and bend it the following spring before bud break.

Step 4: getting buds to break along the arm

Once the arm is tied flat, buds should break along its length during the first growing season. Horizontal training reduces apical dominance, the pull that would otherwise send most vigour to the tip. Buds on the top and sides of the arm then have enough strength to form the future fruiting spur system.

A bare patch can be encouraged by nicking the bark just above a dormant bud with a clean knife. The small wound interrupts the flow past that bud and can push it into growth. Do this in early spring before the sap is fully running.

On a Cox arm of 60 to 80 cm, six to ten viable shoots along the length are enough. At maturity, a step-over of that size may carry about 1.5 to 2.5 kg of fruit.

Step 5: summer pruning with the Modified Lorette system

Summer pruning is the work that keeps the tree at step-over height. The Modified Lorette System, set out by the RHS for trained apples, cuts back the current season’s shoots in mid to late summer once their bases have firmed and the first three leaves have turned woody.

Cut mature laterals that grow directly from the main arm back to three leaves above the basal cluster. Shoots growing from existing spurs are shortened harder, to one leaf above the basal cluster. In the south of the UK this often falls around mid-July; in the north it usually moves into August. Judge the moment by the firming of the wood.

Soft green pruning is too early. It commonly triggers a flush of secondary regrowth, which then needs another cut in September. The summer cut sends energy into fruit bud formation for the following year, allowing a tree this small to crop.

A single Cox step-over might carry forty to sixty shoots needing this treatment across the arm. The work may take about twenty minutes, with one repeat pass if secondary shoots appear.

Feeding the root zone

Apply a balanced general fertiliser such as Growmore at about 70 g per square metre over the root zone in late winter. Follow it with a mulch of garden compost or well-rotted manure, keeping the material clear of the graft union. M27 cannot forage far, so the feed has to sit where the roots can use it.

Steps 6 and 7: thinning spurs and renewing tired wood

After four or five years, the spur system on an older step-over becomes crowded. A spur that began as one fruiting point can branch into a cluster carrying more flower buds than the little tree can ripen into good Cox apples. Crowded spurs produce many small, poorly coloured fruit.

Do the spur thinning in winter. Remove the oldest, most congested spur branches completely with a clean cut, and shorten others so each cluster carries two or three fruit buds. Leave spurs roughly 10 to 15 cm apart along the arm. Cox is prone to bitter pit and to biennial cropping when overloaded, so this thinning matters more with Cox than with a more forgiving variety such as Discovery.

Renewal is the seventh step. Over a decade, an arm lengthens and the oldest wood at the base loses fruitfulness. When cropping has moved towards the tip, cut back a tired section to a younger replacement shoot that can be trained along the wire. Tie that new growth in so it takes over the productive run.

The purpose is to keep the full 60 to 80 cm of arm in useful bearing. M27 is short-lived compared with a tree on MM111, and a Cox step-over may have a working life of about fifteen to twenty years before the rootstock itself declines. Renewal pruning helps carry the cordon through that span.

Pollination remains a special point with Cox. The variety is partially self-fertile, yet it crops far better with a compatible partner in flowering group 3 within bee range. James Grieve or a crab such as Golden Hornet can supply that pollen. A single step-over in an isolated garden may set only a light crop, and the missing factor can be pollen even when the training and pruning are sound. Even with that pollen source nearby, this remains a very small frame for a demanding apple.