This latest report on Sparkling Wine in the UK from Wine Intelligence is now available.
How to select the correct rootstock
The majority of rootstocks used today originate from crosses of three American species:Vitis riparia, V. rupestris, V. berlandieri.
Vitis riparia rootstocks are low in vigour, but suffer from iron deficiency (chlorosis) in chalky soils
Vitis rupestris rootstocks are very vigorous, with a deep rooting system, but are also very susceptible to chlorosis
Vitis berlandieri is very vigorous and deep rooting and has a high resistance to chlorosis. Its cuttings have a very poor ability to root, and so it is rarely used as a pure species.
Many hybrids of these species have been developed, and the correct choice depends on many factors:
- The calcium content of the soil. This can be measured as a percentage, as a pH, or as the index of potential chlorosis (IPC). The latter takes into account the size of the chalk particles and the total iron content. If in doubt, go for a Vitis berlandieri hybrid.
- The vigour of the vine required. This will also be influenced by the fertility of the soil, so that a vigorous rootstock may be used for poor soils and a weak one for fertile soils. The plant density and training system selected must relate to the vigour of the vines.
- The depth of soil: use vigorous, shallow rooting rootstocks in shallow soils.
- The water-holding capacity of the soil. No rootstocks will permit the production of quality grapes on very humid soils, but Vitis riparia-based hybrids are generally more tolerant of damp conditions, whereas Vitis rupestris-based hybrids are more drought tolerant. Some rootstocks are more sensitive to soil compaction that others
- Soil acidity and salinity. Excess acidity can lead to aluminium toxicity problems in some rootstocks, and some rootstocks (e.g. Salt Creek) have been specially bred for saline soils.
- Vine cultivar.Some rootstock/scion matches are not advisable, for instance, cultivars with problems at flowering or wood-ripening should not be grafted on to vigorous rootstocks
- Climate. Weak vigour rootstocks are usually used in cooler climates, as they shorten the vegetative cycle.
- Yield and quality required. In general, only weak to moderate vigour rootstocks should be used in quality wine production.
The principal rootstocks used in the UK are 5BB, SO4, 5C and 125AA. These are all riparia x berlandieri hybrids: surface rooting and with a high resistance to Phylloxera and chlorosis.
In order of decreasing vigour:
|5BB||Is very vigorous and suited to a very wide range of soils (humid, compact, clay, shallow). Suitable for low-density systems, such as GDC, and often used with Seyval Blanc, which is a weakly vigorous, but strongly flowering cultivar.|
|125AA||Particularly useful for soils which are poorly drained, or for poor stony dry soils, but not heavy clay.|
|5C||Suitable for a wide range of soil types, except for extremely dry soils|
|SO4||Is a bit less vigorous than 5C, but suited to a very wide range of soil types, particularly fertile, humid soils. It can have problems with taking up magnesium from the soil (leading to peduncular atrophy), and so may require foliar feeding.|
3309C, 101-14, 161-49C and 420A may also be of interest in the UK.