14 Cordon Tomatoes Trained up Haxnicks String on a Greenhouse Ridge

String tension carries the crop

Haxnicks tomato support string is jute twine sold on 50 m rolls. In a cordon row, its main job is to give the stem a surface to climb. The knot only fixes the line; the crop is carried by the way the plant is wound around the fibre.

The line is tied to a ridge wire or overhead bar, dropped to soil level, and fixed at the base with a loose loop or a buried anchor. As the plant grows, the leading shoot is wound clockwise around the twine every few days. A useful rate is about one full turn for every 20 cm of new growth. The stem grips the jute as it thickens, so the plant can be supported without clips or tight ties cutting into it.

Tension decides how well the system behaves. A slack string lets a truss carrying 1.5 kg of ripening fruit pull the vine sideways. A string pulled too tight can lift the rootplate when the plant sways in a ventilated house. The working feel is firm, with about a centimetre of give when plucked. Fourteen plants on one ridge means fourteen separate tensions, and the two plants nearest the gable ends usually catch the strongest draught, so they need tighter winding and more frequent checking.

Side-shooting without losing track

A cordon tomato is run as one stem. At each leaf axil, where a leaf joins the main stem, the plant tries to produce a side-shoot. Left to grow, that side-shoot becomes another stem drawing on the same root system. Indeterminate varieties such as Sungold or Shirley need those shoots removed every week while they are still 2 to 3 cm long. At that size they snap away cleanly with a sideways thumb flick.

With fourteen plants, the common failure is missing one axil. A side-shoot left until it is 15 cm long needs cutting with a knife, leaves a larger wound, and has already taken a week of sugar into foliage that will be removed. The easiest routine is directional: start at the door end, work along the ridge, and touch every axil from top to bottom before moving to the next plant. At around 40 seconds per plant, the full pass takes under ten minutes.

If the growing tip snaps, the topmost side-shoot can be kept as a replacement leader. It is wound onto the same string and becomes the new cordon. The growth below it stays single-stemmed.

Basil, marigolds, and the soil line

Basil and French marigold, Tagetes patula, sown in the border soil between tomato stems have practical value in this layout. Marigold roots release alpha-terthienyl, a compound toxic to root-knot nematodes in nearby soil. Their flowers also draw hoverflies, whose larvae eat aphids on the soft tomato tips exposed by regular side-shooting. Basil is a small competitor because its roots stay shallow while the tomato roots feed deeper.

The smell-alone explanation for whitefly repellence runs ahead of the evidence. Along a greenhouse ridge, the reliable benefits are predator habitat and ground cover. Covered soil crusts and dries less between waterings. In a 14-plant run, a marigold in every second gap and a basil in the others gives a low border crop as well as cut-and-come-again herbs within reach while pruning.

Keep companion foliage away from the tomato stems at soil level. Damp growth bunched around the base is where Botrytis grey mould starts, and grey mould can travel upward through the wounds left after side-shoot removal.

Feeding once the first truss sets

Once the first truss has set pea-sized fruit, the plant’s demand shifts from leaf growth toward fruit filling. That is when a high-potash tomato feed such as Tomorite, or comfrey liquid diluted at about 1:10, goes in with the water. In border soil this is typically twice a week. In grow bags, where the root volume is small, feeding may rise to daily.

The plant shows the balance. Too much nitrogen gives lush dark foliage with sparse trusses. Too little potassium shows as yellowing margins on older lower leaves while the top remains green.

Water volume matters alongside feed strength. A mature cordon in July loses a great deal of water through its leaf area, and irregular moisture is the direct cause of blossom end rot, the sunken brown patch at the base of the fruit. The patch develops when calcium fails to move into the fruit as the plant dries. In most British soils, calcium is already present. Even moisture corrects the problem more reliably than a calcium spray.

Powdery mildew on courgettes nearby

Greenhouse borders often carry more than tomatoes, and a courgette in the corner can show powdery mildew by midsummer in warm, still weather. The disease appears as a white dusty coating on the upper leaf surface. A milk spray made from one part full-fat milk to nine parts water, wetted onto the leaves in morning sun, uses light-reactive milk proteins to suppress the fungus; it should be reapplied after rain or heavy watering and repeated weekly.

Cutting out the oldest, worst-affected leaves improves airflow. Powdery mildew thrives in still humid air, and it can germinate without leaf wetness, which is why it appears even on plants kept dry at the leaf.

Ventilation around a wall of cordons

Roof vents open, the door propped, and fourteen cordons wound up strings can form a vertical wall of leaves. Depending on how the trusses hang, that wall either channels air along the ridge or holds it in the foliage.

Once the bottom truss ripens, stripping the lower 30 cm of stem opens a floor-level airflow gap. That single strip is one of the strongest moves against grey mould and blight. It also lets low light reach the border soil where the basil and marigolds are growing.

Humidity is the mechanism behind many greenhouse tomato diseases. If the house sits above roughly 85 percent relative humidity overnight and the leaf surface falls below the dew point, a film of water forms. Spores of Phytophthora infestans, late blight, germinate in that film.

Evening ventilation helps the house dry before nightfall. Automatic vent openers with wax-piston mechanisms, such as Bayliss or Gigavent units, open at around 15 to 17 degrees and close as the house cools. They handle the daytime heat spike when nobody is there.

Overnight drying still depends on leaving a vent cracked. The string method concentrates every leaf and truss into a narrow footprint, so ventilation is built into the layout itself.

Fourteen plants in single file dry fastest along the outside faces and slowest in the leaf mass at head height. That dense middle is the place where the first grey fuzz is most likely to be seen.

The late July pinch

By late July, several jobs tend to land together: winding, side-shooting, feeding, leaf-stripping, milk spray on the courgettes, and truss-thinning. Fourteen cordons past head height may each be carrying five or six trusses, with the growing tips reaching the ridge wire. At that stage, the plants are stopped by pinching out the top two leaves above the highest truss, pushing the remaining energy into ripening the fruit already set.

Stopping time is the awkward part. Pinch out early in a long warm season and the plant loses trusses it might have ripened before the first October cold. Leave the tips running late and the upper trusses can swell green without colouring before the light fails. Variety, greenhouse latitude, and autumn warmth all affect the call, and a calendar date alone cannot settle it for a specific ridge.

Late stopping has a plain visible marker: the upper fruit may be swelling while the season is already losing light. Along this ridge, the unanswered part is how much green weight at the top deserves space when the lower trusses have started to colour.