In the 1960s and 1970s, research at Long Ashton Research Station showed that several varieties of ornamental ‘crab apples’ performed well as pollinators for commercial varieties of apple such as Cox and its clones (Williams, 1977). Malus aldenhamensis, M. ‘Golden Hornet’, M. ‘Hillierii’ and M. ‘Winter Gold’ were all suggested as suitable pollinating varieties.
Since this initial research, several other varieties such as ‘John Downie’, ‘Evereste’ and ‘Golden Gem’ have been added to the recommended list, following research conducted in France (Le Lezec and Babin, 1990) and the UK.
Flowering crab apples with proven value as pollinators:
- Malus aldenhamensis has a weak growing habit with slender twiggy branches easily distinguishable from most fruiting varieties of apple. It flowers regularly and abundantly and the flowers produce large quantities of viable pollen.
- Malus floribunda Hillierii is another weak growing crab with thin drooping branches, very distinct from most fruiting varieties. Flowering is abundant and regular and flowers on one-year-old wood help provide a long flowering period. Pollen production is also good. This crab exhibits high resistance to disease.
- Malus Winter Gold. In trials at Long Ashton, pollen of Winter Gold, proved poor in pollinating Spartan, Golden Delicious and Cox in 1981 (Williams et al., 1982).
- Malus Golden Hornet. A popular pollinating variety in orchards of Cox planted in the 1980s, Golden Hornet does tend to release its pollen prior to opening its flowers and this may occasionally prove problematic (Anon, 1972b).
- Malus Evereste and Malus Professor Springer. These varieties have become popular in Holland and Belgium and are being used successfully in UK orchards though no efficacy studies have been done in the UK.
Use of these crab apple pollinators has advantages:
- They take up minimal space in the orchard and they require no harvesting.
- The traditional planting ratio for Malus pollinators was one tree every three trees of the main variety in every other row of the latter.
- No extra space in the row was provided for the pollinator; the small tree was fitted between two trees of the main variety at their standard spacing.
It is fortunate that most species of Malus are cross compatible with dessert and culinary apple scion varieties and no problems of pollen compatibility are likely when using these species.
- To ensure adequate overlap of flowering dates with the main orchard fruiting variety, use of 2 to 4 different Malus types is recommended in the same orchard.
In studies undertaken in 1979, scientists at Long Ashton calculated the amount of pollen produced by either normal pollinating varieties or Malus selections, and also the time of flowering relative to Cox (Church and Williams, 1980).
- The records show that when weather conditions in the spring are unfavourable poor synchrony of flowering may be a problem with some of the Malus species.
- The best pollen yields per tree on trees planted in 1975/6 came from Malus Winter Gold, Hillieri and Aldenhamensis.
- However, good pollen yields were also obtained from trees of the more conventional pollinators James Grieve and Golden Delicious.
Flowering time and pollen production in 1979 on apple varieties and ornamental Malus planted at Long Ashton Research Station (from Church and Williams, 1980)
| Variety or Malus species | Flowering time, days before (-) or after (+) Cox | Mean wt. of viable pollen (g) | ||||
|---|---|---|---|---|---|---|
| 50% open | 80% open | |||||
| Spurs | Axillary | Spurs | Axillary | /cm2 CSA of trunk | /tree | |
| Discovery | -5 | +3 | -9 | +3 | 0.11 | 1.49 |
| Egremont Russet | -5 | +4 | -9 | +7 | 0.05 | 0.79 |
| Emneth Early | -1 | +11 | -5 | +6 | 0.07 | 0.88 |
| Golden Delicious | 0 | +8 | -3 | +6 | 0.13 | 2.19 |
| Grenadier | -2 | +10 | -5 | +6 | 0.02 | 0.20 |
| James Grieve | -5 | +9 | -9 | +6 | 0.15 | 2.26 |
| Lord Lambourne | -5 | +1 | -9 | -1 | 0.11 | 1.30 |
| Worcester Pearmain | +1 | +9 | -3 | +7 | 0.03 | 0.32 |
| Golden Hornet | -1 | 0 | -3 | -1 | 0.34 | 3.95 |
| Hillierii | +3 | +9 | 0 | +6 | 0.60 | 3.56 |
| Alderhamensis | +4 | +7 | +1 | +4 | 0.30 | 1.97 |
| Winter Gold | +1 | +6 | -1 | +4 | 0.45 | 5.82 |
Use of ornamental crab apples as pollinators in overseas orchards
Research in other countries has also resulted in recommendations for use of ornamental crab apples in USA, German and Dutch apple orchards (Crasweller, et al., 1978; Stainer and Gasser, 1982; Witteveen, 1973).
- In research conducted in Sweden in the early 1980s the flowering times of a range of ornamental crab apples and several fruiting varieties were recorded over a four year period (Goldschmidt-Reischel, 1993).
- The results are shown below.
Rankings of earliness of flowering of ornamental crab apples used as pollinators in apple orchards in Sweden
| Variety | Earliness Rank | Variety | Earliness Rank | Variety | Earliness Rank |
|---|---|---|---|---|---|
| Dolgo | 3 | Akero | 36 | Golden Hornet | 49 |
| Robin | 4 | Silva | 36 | White Angel | 50 |
| Hopa | 25 | Kim | 39 | Aroma | 51 |
| M. sieboldii | 29 | M. baccata | 40 | M. floribunda | 51 |
| M. zumi caloc | 30 | Snowdrift | 42 | Royalty | 52 |
| John Downie | 31 | Katy | 42 | Van Eseltine | 54 |
| Hyslop | 31 | Mio | 44 | ||
| Kerr | 33 | M. Eleyi | 47 | ||
| Rosencrab | 35 | Ingrid Marie | 49 |
Rankings of stage of flowering (all recorded on the same day) range from 1 to 71. 1 is very early (all flowers at petal fall stage) and 71 very late (all flowers still in bud). (From Goldschmidt-Reischel, 1993).
Several species of ornamental Malus can prove effective pollinators for commercial varieties of dessert and culinary apples.
- They have the advantage of taking up less space in the orchard than normal pollinating varieties.
- The tried and tested species/varieties are M. hillierii, M. aldenhamensis, M. Golden Hornet, M. Winter Gold and M. Evereste.
- Always plant several of these ornamental crab pollinators in an apple orchard, not just one.
- Their winter chilling and spring forcing temperature requirements are different from those of the commercial apple varieties and this often leads to lack of synchrony in flowering times.
- Do not neglect the pruning and, where necessary, the thinning of ornamental crabs, or they may go biennial and fail to produce the required flowers in sufficient abundance.