9 Step Espalier Apple Tying Routine with Discovery on M9 Rootstock

M9 is a dwarfing rootstock, and on Discovery it usually keeps the mature tree to about 2.0 to 2.5 metres. That size is the reason the frame needs galvanised straining wire set at 40 cm vertical spacing, with a Gripple tensioner at each post. M26 gives more height and tends to pull against the horizontal training. M27 sits further down the dwarfing scale and can leave the spur system short of vigour before the third tier has filled. The routine below assumes a two or three tier horizontal cordon already pinned to the wire, with a central leader still supple enough to bend without tearing the cambium.

Step 1: Read the cane before tying

Walk the tree first and separate the current-season extension growth into three groups: the leader continuation, the lateral that can become the next tier arm, and surplus growth competing with both. On Discovery, extension wood stays reddish and pliable until late August. After that, lignification stiffens the cane and winter work becomes the safer route.

A lateral thicker than a pencil at its base, roughly 7 to 8 mm, has moved beyond the easy-bending stage. To lay it flat, partial nicking on the underside may be needed.

The geometry matters more than the number of shoots. Two tiers at 40 cm and 80 cm cover about 1.6 square metres on a standard 1.8 metre fence panel, and that area limits how many fruiting spurs the tree can ripen before it shades itself. Mark the keepers with a loose jute loop before cutting, because the reference points disappear quickly once surplus shoots come off.

Step 2: Pick tie material for the load

Soft 4 mm hollow rubber tie expands as the limb thickens and can accommodate a Discovery arm that adds 6 to 9 mm of girth in one season. Jute twine usually rots through in about eighteen months, which makes it useful for temporary leader bending and weak for a permanent cordon arm. Polypropylene flexi-tie falls between those uses: it can be reused across seasons, with a deliberate finger-width gap at the knot so the cambium has room.

Wire gauge changes the choice as well. A 2.5 mm galvanised wire under tension can saw into a soft rubber tie within two summers if the tie is cinched directly against it. The usual answer is a figure-of-eight that holds bark clear of the metal, with the arm supported in the tie loop.

Step 3: Bend the leader to 45 degrees first

Taking a young Discovery leader straight down to horizontal in one movement often splits the base. The lower cambium is compressed while the upper side is stretched. In the first season, bring the leader to 45 degrees and tie it there. The following spring, once the wood has set at that intermediate angle, lower it to horizontal. On vigorous M9 stock, that two-stage bend often separates a clean cordon from a broken one.

Felco No. 2 or the lighter Felco No. 6 handles the relief cuts cleanly. A sharp blade matters because a crushed cut on a limb under bending stress invites canker. When working along a row, wipe the secateur blade with isopropyl between trees, since Discovery is moderately susceptible to Nectria galligena and a contaminated blade can carry it from arm to arm.

Step 4: Make the figure-of-eight and test the give

Every permanent tie follows the same path: one loop around the wire, a crossover, one loop around the arm, then a knot finished on the wire side where it cannot rub the bark. Set the tightness by hand. The arm should stay where it has been trained when released, while still shifting 3 to 5 mm under a firm push. If the limb is held rigidly, the phloem can be strangled by midsummer.

Place roughly one tie every 25 to 30 cm along a horizontal arm. Wider spacing lets internodal sections bow upward toward the light, interrupting the horizontal line that suppresses apical dominance and encourages spur production.

Step 5: Stop upright regrowth early

Horizontal training makes dormant buds along the top of the arm break into vertical shoots. On Discovery, those shoots can reach 30 cm by late June.

Rub out soft upright shoots with a thumb while they are still under 5 cm. If one escapes and turns woody, use the Modified Lorette cut in the third week of August: shorten it to three leaves above the basal cluster, which can turn the shoot into a fruiting spur within two seasons.

Step 6: Space and renew the spur system

Discovery fruits on two and three year spurs. Left alone, it builds congested spur clusters that shade the apples growing from them.

Every third winter, thin the spur system to about 10 to 15 cm spacing along the arm. Remove the oldest, most branched spur by cutting it back to a single fruiting point.

A mature Discovery cordon arm carrying eight to ten well-spaced spurs ripens larger, redder fruit than the same arm crowded with twenty. The fruit needs direct light to colour properly, and any spur sitting in the shade of its neighbours produces apples that taste thin and watery. That is the whole argument for opening the cluster.

Renewal is what keeps an espalier productive after year eight. Each winter, find one spur system per arm that has fruited three or four times and has begun to produce undersized apples. Cut it hard back to a stub with two buds. One of those buds should break as fresh replacement wood the following spring.

Rotate that renewal across the framework. If all the old spurs are left to age together, a fifteen year old espalier can become a mass of unproductive twigs.

Keep the tiers in balance while thinning. The lower arm on most wall-trained Discovery trees outpaces the upper arm because it sits nearer warm masonry and catches reflected heat. Prune the lower spurs a little harder to keep the two tiers roughly even. If the upper tier remains weak after two seasons, leave its laterals one bud longer at the August cut to draw sap upward.

Around year ten, another decision can appear on a tier that has lost vigour at its tip. The grower may keep renewing spurs on the original arms, or bark-graft a fresh extension onto that tier. Tying can hold an arm in productive order, but it cannot reverse the slow decline of cambium at the far end of a two metre cordon. At that stage, renovation cost has to be weighed against the value of starting a replacement maiden.

Step 7: Tie with the pollination window in mind

Discovery is a triploid-tolerant diploid in flowering group 3. It sets best near a group 2, 3 or 4 partner, such as James Grieve, or a crab apple such as Golden Hornet, within roughly 18 metres.

The blossom still has to meet compatible pollen. Framework geometry affects that timing. A heavily tied tree held tight against a cold north wall opens later and can miss the partner’s peak bloom. South or west aspect tying can bring Discovery blossom forward by several days, improving the overlap.

Step 8: Retension in August

A tie set in spring slackens over the season because the arm beneath it keeps thickening. The wire behaves differently: summer heat expands the galvanised strand, so the same tie can be loose at the knot and tight against the metal at once. Both effects argue for a midseason check in the third week of August, which combines neatly with the Lorette pruning.

Relieve any tie pressing a visible groove into bark, add ties where an arm has bowed, and remove temporary jute from any leader that has set at its intended angle. A tie left to girdle through a full summer can ringbark a Discovery arm badly enough that the wood beyond the wound starves and dies back by the following spring.

Step 9: Use the bare winter framework

Between leaf fall and bud movement, usually December through February, the bare framework shows faults that foliage hid. Sight down each arm for upward bowing, replace perished jute with rubber tie, and make the spur-renewal cuts from Step 6 while the structure is fully visible.

Pick a spell of cold dry weather for these cuts. Canker spores travel in wet conditions, and a Discovery wound seals slowly once the temperature drops below 4 degrees, so a frosty still morning gives the cleanest result. If the far end of any tier looks thin after you have sighted down it, that is the spot to watch through the next growing season before deciding whether the arm is worth renewing or replacing.