Soils rich in nitrogen and with copious supplies of water induce strong shoot growth and reduced numbers of flowers per metre of shoot length. These flowers are often initiated late in the summer season on account of the prolonged period of extension shoot growth on the vigorous trees. Such late initiated flowers are inevitably poorer in ‘quality’ the following spring than flowers initiated earlier in the summer.
Young trees
- Obtain analyses of the soil mineral and organic matter contents prior to tree planting. Based on these analyses and the current recommendations concerning optimum levels (e.g. Defra recommendations in RB 209) any necessary base dressings should be applied.
- Supplementary nutrition of trees in their first or second years following planting should be applied in order to maximise early yields. This is best done by a combination of fertigation and regular applications of a balanced foliar feed.
- Where this is not possible, apply repeated small doses of a blended fertiliser or a slow release fertiliser in the planting hole.
- On deep fertile soils that have never been planted with apples these supplementary treatments may not be necessary.
- In all cases monitor the tree nutrient levels by leaf analysis during the establishment phase.
- Supplementary irrigation should be applied, preferably using trickle systems, only when soil moisture deficits reach 50 mm.
- Recent work has shown the benefit in improving establishment and early yields of using a shallow mulch of composted green waste. This should be used where irrigation is not possible and can give added benefits even where irrigation is applied.
- On varieties sensitive to bitter pit, care should be taken to only apply a light mulch just after planting as mulch material can contain high levels of potassium. Always ask for, or carry out, a mineral analysis of the compost and ensure that it conforms to the latest British Standards.
Mature trees
Avoid excessive use of nitrogenous fertilisers in the early part of the growing season. These fertilisers stimulate excessive growth and have an indirect negative effect on flower quality.
- However, studies have demonstrated that flower quality can be improved by sprays of urea applied either just before harvest or in the autumn following harvesting.
- The reasons for these benefits are thought to be increased meristematic activity in the floral cupula, increased longevity of the ovules and the associated longer EPP.
- It is also suggested that this encourages the spur leaves to develop almost at the same time as the flowers and that this helps flower quality (Stosser et al., 1996).
- Use nitrogenous fertilisers sparingly in the spring and summer prior to harvesting.
- Consider urea sprays in the autumn, following harvesting but before leaf fall to improve the quality of flowers in the subsequent spring.