Kiwi fruits (Actinidia deliciosa and Actinidia arguta) are exotic fruits that are actually surprisingly easy to grow in the UK, especially if you have space in your polytunnel. As long as you have a warm and sunny location and can provide them with the space and support they need, they can reward you with a good yield over a number of years.
A large part of growing kiwi successfully lies in choosing the right growing location and making sure that the plants get the growing conditions they need. In part, the preferred and required conditions depend on which species of kiwi you have chosen to grow.
However, remember that all kiwis need as warm and sunny a location as possible, and a fertile, well-drained growing medium or soil rich in organic matter, with a slightly acidic pH.
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There are two different species of kiwi that can be grown in the UK: Actinidia arguta and Actinidia deliciosa.
Hardy kiwi – Actinidia arguta
Native to East Asia, the hardy kiwi, also known as Tara vine, is a deciduous climber that will grow up to almost 50ft in height. It is hardy and not frost tender. It provides a long period of interest – being in leaf from May through November, and flowers from June to July in full sun or semi shade. The fruits are smooth skinned, unlike the kiwi, their relative, and the skin can be eaten with the fruits. If you plan to grow just one, you will need a self-fertile cultivar, such as 'Issai'.
Kiwi - Actinidia deliciosa
This is the furry-skinned kiwi like those with which most people are familiar from supermarket stores. These produce larger fruits than the above. If you wish to grow this type of kiwi then you should note that it is less hardy than the above, and you should carefully select a variety that is suited to cultivation in the UK. Most varieties need a pollination partner, and you will need male and female plants to obtain fruits.
As long as you select a suitable cultivar or cultivars for the growing conditions that we can provide here in the UK, Kiwis are not actually all that challenging to grow.
Once you have selected and sourced your plant, the first thing that you need to do is prepare the growing area. Kiwis can potentially be grown in large containers but as vigorous vines, they will do best when grown in the ground.
Make sure that the soil in your chosen growing area is well-weeded and enriched with plenty of organic matter before planting, so your new kiwi or kiwis get off to the best possible start.
Before planting you will also need to make sure that you have your trellis or other support structure for these vining plants in place.
Kiwis are usually best planted out in the spring, once the last frost date has passed, and the soil and air have begun to warm. If you have more than one to plant, you should plant with around 3-4m between the plants to ensure that they do not compete too much with one another.
Water in your new addition but make sure that excess water can drain away freely. Mulch around the base of your kiwi vine with homemade compost or other organic matter.
Kiwis need some care in order to perform well and to fruit successfully. Watering, mulching, feeding and protecting the plants from frost are key concerns, though training and pruning is where the most time and specialist knowledge is required.
When grown in a polytunnel, kiwis will of course have to be watered carefully throughout their lives. Outdoors, once established, kiwis can often cope with natural rainfall alone but will need to be watered during the growing season for their first couple of years, until they become established in their growing location.
Water well during dry spells or when growing undercover, and especially make sure plants get enough water while the fruit forms. But make sure waterlogging does not occur or the roots may rot. Good drainage is essential to success.
Mulch upon planting out a kiwi and renew the mulch around the base of the kiwi plant each spring. But make sure that the mulch does not touch the stem at the base or this can rot. Leave a gap of around 5cm around the base of the vine mulch free.
Kiwis will appreciate a high potassium organic feed once growth begins in the spring. This should help the plants to flower and fruit successfully.
Hardy kiwis are hardier of the two species, but even these can experience frost damage to tender new growth in the spring. If young shoots are damaged by frost this can severely curtain its growth for the season.
So keep an eye on the weather forecast and cover your kiwi if a frost threatens after growth has resumed at the beginning of the growing season.
You should also keep an eye on the weather in autumn, and harvest and bring fruits indoors before the first heavy frost. Fruits that are not quite ripe will continue to ripen indoors.
Kiwi vines can be propagated by means of softwood cuttings, layering, or grafting using the whip-and-tongue method. Cuttings are typically the easiest option and these should be taken in spring, from fresh, new growth. Rooting hormone will increase chances that cuttings will root successfully.
These vigorous vines do need to be managed carefully, especially where space is limited. So when growing kiwi you will need to give some careful thought to training and pruning.
The key thing to remember when training and pruning kiwi is that the fruits grow on the shoots of the previous season, and the oldest part of the previous year's shoots should be retained.
Kiwis will do best when trained and pruned, as when kiwis are left to their own devices, they can often focus on vegetative growth rather than on fruit production.
Kiwis can be trained to grow up any trellis type structure, or over a pergola, arch or other garden structure. They can also be espaliered against a wall or fence with horizontal wires in place.
Kiwis are usually pruned upon planting and then twice annually – in the winter and during the summer months.
If you are growing a kiwi on a trellis or as an espalier, initial pruning and training involves pruning the leading, strongest shoot to 30cm in height, the training two side shoots horizontally to each side of this main stem. Pinching the tips of these side shoots will encourage branching.
To develop new tiers on an espaliered plant, allow side shoots to form new laterals at 20-30cm intervals. Pinch the tips of each after 5 leaves to encourage strong growth and branching. Continue to train the shoots along horizontal wires, spaced around 40-50cm apart.
An established kiwi should be pruned in winter and summer. In winter, prune side shoots to 3-4 buds beyond the last fruited stems, and each year prune out around ¼ to 1/3 of the oldest horizontal stems to buds around 5cm from the main shoot.
In summer, from June onwards, pinch back fruiting shoots to leave 4-5 leaves beyond maturing fruits. Prune any non-fruiting horizontal shoots to five leaves, and any regrowth to one leaf past the last pruning cut.
Kiwis will need a warm, long summer in order to fruit well, which is why they will usually do best when grown undercover in the UK.
Often, UK growers will find, even undercover, that kiwi fruits are not fully ripe at the end of the growing season. Fortunately, as mentioned above, they will continue to ripen off the vine, indoors, over the next few weeks.
You can tell that kiwis are ripe because they will give slightly when you give them a squeeze.
As mentioned above, you can choose between hardy kiwis, Actinidia arguta, and kiwis, Actinidia deliciosa. There are some named cultivars and you need to determine whether specific varieties are self-fertile or not, as many are not and you will need to grow males as well as females to get fruits. Make sure when selecting a named varietal that you select one that is suited to growing in the UK.
Many of the most common problems that can arise when growing kiwi arise because of some deficiency in the growing location, environmental conditions or care.
For example, damage can occur where frosts can reach new growth in the spring. Drought, under-watering or drying winds can cause damage to leaves which can turn brown along their edges. If the soil is on the alkaline side, and chalky, nutrient deficiencies can be common. Waterlogging can lead to root rot and exacerbate fungal issues.
Fungal issues to which kiwi can fall prey include honey fungus and phytophthora root rot. Fortunately, kiwis are not particularly prone to pest problems.
A polytunnel of sufficient size can make it easier to provide the right conditions and protect the plant from inclement conditions. But remember that these are vigorous vining plants that will need plenty of space and a well-built, sturdy support structure up which to grow.
Paharia, P, T., (2023) Two kiwi fruit every day safe and can replace vitamin C supplementation. News Medical Life Sciences. [online] Available at: https://www.news-medical.net/news/20231127/Two-kiwi-fruit-every-day-safe-and-can-replace-vitamin-C-supplementation.aspx
