Cultivation

Description

The Jujube Zizyphus jujuba is a deciduous fruit tree that can grow to around 7-10m (20-30ft) in height under ideal conditions. Trees are long-lived and can survive for hundreds of years. The foliage is a glossy, dark green - quite attractive when seen shimmering in the light. The leaves are 3-5cm (1-2") long and fade to a pale yellow before falling in late Autumn.

Jujube fruiting branchlets

The Jujube tree has several types of branches. Structural branches maintain the basic shape of the tree. Off these come secondary branches that have a distinctive zig-zag pattern where the branch deviates alternately left and then right at each node. The fruit itself is borne from slender twiggy branchlets that are deciduous. These emanate in clusters from a node on the secondary branch. This photo illustrates this quite well. The fruit will develop on these small branchlets which will hang down under the weight. When autumn comes the branchlets will drop but will shoot again from the same node the following year.

The Jujube awakes from dormancy relatively late in the season. Leaf bud happens around late September and leaf drop in early June in the southern hemisphere (March and December in the northern hemisphere) although this may vary according to climatic conditions. Flowering starts in November (May in the northern hemisphere) which makes the Jujube unlikely to be affected by frosts. They require a full-sun position with long hot days to ensure the fruit will ripen. Trees are very drought tolerant and can survive on minimal amounts of water even in extreme conditions although fruit quality may suffer as a result.

Different cultivars tend to have different growth habits. For example the 'Chico' variety has a distinct weeping habit and almost has an aversion to growing straight up. The 'So' cultivar - renowned for its contorted zig-zag pattern is relatively dwarfish in size. Others like the 'Li' are taller and more upright.

Young trees in particular have very sharp thorns on the branches - be prepared for some blood loss :-)

Jujube flowers

Flowers

There is no blossom as such, the flowers are small (around 8mm in diameter) and a quite non-descript greenish yellow in colour. They are pollinated by bees and small insects such as ants. Flowering lasts for a prolonged period extending over several months resulting in a corresponding long fruiting period. It's common to see mature fruit and new flowers on the tree at the same time.

Planting

Bare-rooted trees should be planted when dormant. Care should be taken to ensure that drainage is adequate and that soil is not compacted so that the roots have somewhere to go. Jujubes are fairly tolerant of soil types and pH but as with any plant they will not thrive if the conditions are too hostile.
Dug well around Jujube tree

Claims that Jujubes will not grow in heavy clay may be exaggerated. Our own soil is a quite firm clay and was suffering from compaction after years of use by grazing animals. It took a mechanical post-hole digger to achieve sufficient depth to get the trees in. However we do incorporate compost or potting mix in a 50/50 ratio into the hole when planting the young trees to make establishment a little quicker. We also lift the trees up slightly to improve drainage.

We always dig a well around our trees to loosen the soil and to catch and hold any rain that falls. Hot, dry areas can suffer a lot from hydrophobic soils where the water runs straight off without soaking in so this helps keep the moisture where it's needed. A little wetting agent is also a must.

Finally we add a layer of mulch around the root zone. Here we're using a gravel mulch - it helps keep the root zone cool, suppresses weeds in the immediate area and can also help stabilize newly planted trees that don't have much in the way of a root system.

Our success rate for bare rooted trees is around 95% in the first year. Some never seem to get going whilst others cling to life for what seems like an eternity before finally giving up. Our philosophy has been that we don't have time for weedy plants so there's no pampering after the first few months. If they can't cope it's just tough - make room for something that can.

Grafting

Fruit from the wild Jujube are very small and can be quite sour in taste. The majority of good quality commercial fruit is from grafted trees where the wild jujube forms the rootstock and the scion is from another variety selected for it's fruit quality.

Claims that related species (such as the Japanese Raisin Tree) can be used as rootstock are varied. Some report that this is possible whilst others say the opposite.

Grafting appears to be extremely technique sensitive in the Jujube. Success rates can vary from 90% right down to 10% or less - quite demoralising if you've ever been there.

Grafting takes place in early Spring when the sap starts to flow in the rootstock plant. Scions must have been harvested from donor plants in advance and may be stored in the fridge if required. The donor wood should be taken in the latter stages of dormancy when the buds are about to re-emerge.

Most of the books suggest whip and tongue grafts but a simple V-graft seems to work just as well. Any grafting book will tell you the basics but the main secrets are

  • A sharp knife with a clean cut
  • Close matching of the diameters of Scion and Rootstock so that the cambium layers match up
  • A good seal to prevent moisture loss - Parafilm works very well for this. Do not skimp

Budding

Some find more success with budding than grafting in Jujubes. Budding takes place slightly later in the season and so it can often be a second chance if grafting has been unsuccessful. It also requires less wood than grafting and so can be more economical in terms of the amount of plant tissue that needs to be harvested from donor plants.

Budding involves taking a bud from a fruiting cultivar and inserting it into or underneath the bark of the rootstock plant. T-budding is probably the most common method where a T-shaped incision is made in the bark of the parent plant and the bark gently teased back to allow the insertion of the 'shield' - the stripped-down donor bud.

T-budding requires the bark to 'slip' or separate cleanly from the underlying layers and is therefore restricted to periods when the tree is in an active growth phase. This is typically from mid Spring to early Summer but it can vary according to local conditions. Jujube trees have quite thin bark and so it can split a little too easily so care is required. Chip budding is an alternative method which has gained popularity among orchardists growing other fruit types as it can be done over a wider time window. Again there are no special techniques here and any budding/grafting book will teach you the basic technique.

Maintenance

Root sucker of Zizyphus jujuba
The rootstock tends to 'sucker' quite badly - particularly when young. Suckers should be removed frequently, initially these will be close to the base of the tree but in later years can appear from the roots some distance from the trunk. Removal is by cutting or pinching them off when young. If you do this regularly it's quite easy but if you leave it too long the suckers can get woody and you need secateurs or a hoe to remove them. We perform this task weekly and it makes the job much quicker and easier as the new growth hasn't had time to mature and can usually be plucked out whole.

We try to avoid staking where possible but in some cases this is not practical. Binding trees to stakes should always be done loosely to allow a degree of movement otherwise the tree will learn to rely on the stake for support which is counter-productive.

Growth rate of young Zizyphus jujuba tree />
<h3>Location</h3>
<p>Jujubes can survive under many conditions but need full sun and warm, dry summers to thrive and produce a good crop. If planting multiple trees then a minimum spacing of 4m is recommended to avoid competition for light. The Chinese traditionally use much larger spacings but they grow other crops in between the rows. If you need to net your trees to avoid damage by birds then spacing is a crucial decision that you have to make as spacing equals money in terms of the amount of net required.</p>
<p><br /></p>
<h3>Feeding</h3>
<p>Jujubes do quite well without any special care but they do respond well to a dose of fertiliser early in the growing season.  Poultry manure works extremely well but make sure it is well aged as fresh manure is known to be very

This image shows a grafted tree that has been in the ground for 14 months. Chicken manure was applied around the base just before the breaking of dormancy at around the 12 month mark. The rate of growth is quite astounding. As you can see the tree has pretty much doubled in size within the first few weeks of the new growing season

  • A - tree height when initially planted
  • B - tree height after 8 months (end of first season)
  • C - tree height after 14 months

Watering

Last years and this years growth
Again Jujubes are not fussy and can survive extended periods of drought and what seems to be extreme temperatures. The summer of 2010 saw some extreme conditions in our region - our average daily maximum temperature in January was 36.6 celcius (almost 100F). That's the average temperature - there were many days in the 40s. At the time our water supply was scarce and we watered the trees only 5 times during the entire summer. Not many other plants could tolerate those extremes except maybe succulents and a few desert plants.

However you do need water for the trees to grow and fruit well. This will be our first commercial season so we have now installed a drip irrigation system which we will use on a weekly basis in the hotter months. We have 2 x 8 Litre/hour drippers per tree which will provide one deep watering per week. Less frequent but extended watering is preferable to less water more often as it encourages the roots to go down into the soil rather than just staying on the surface. It's early days so we may change this regimen but we know the trees can cope so this is less of an issue.

It is reported that the Jujube can also survive relatively high levels of salt in the water, making it possible to use ground water for irrigation. However we would urge anyone doing this to first measure the salinity of their ground water and also be aware that continued application can cause a build up in the soil if it is not flushed away with fresh water. Rain will help do this but there are limits to what the soil can take - particularly if it has a high clay content. Get an electrical conductivity (EC) meter to do this- inexpensive ones can be found on eBay for under $30 and are well worth the investment.

Soil pH

Jujubes are able to grow in a wide range of soil pH's. A range of 5-8 has been suggested but at the extremes you may get some trace element deficiencies. Be aware that the pH scale is logarithmic rather than linear. This means that a change of 1 unit equates to a 10-fold change in acidity. So for example, "Neutral pH" is 7, pH 6 is acidic but pH 5 is ten times as acidic as 6.

It has been said that Jujubes prefer a well drained, slightly alkaline soil but having said that ours are thriving in our heavy clay with a pH of 5.6 so we often take claims like these with a large pinch of salt. That's the thing with Jujubes, there's so little good information around that one person's opinion can be reproduced all over the place and become 'fact' when it is nothing of the kind.

Insects pollinating Zizyphus jujuba flowers

Pollination

Pollination is by small insects - primarily bees and ants but as this photo shows just about anything can get in on the game. According to the books, the flowers only have very short period in which they are fertile so a large and varied insect population can be an asset.

Plants are self fertile but, as with most fruit trees, they produce more and bigger fruit when cross pollinated by other trees.

Vertical shoots

Pruning

Most books say that pruning is not required and that unpruned trees produce as well as pruned ones. However in our experience young trees need a degree of pruning to achieve a good shape. This is particularly true for those with a weeping habit such as the Chico that seem to prefer growing sideways rather than upwards.
Low branches should be pruned off to encourage a longer trunk. Pruning also lets in more light and this will help ripen whatever fruit there is.

This year a number of our younger trees have started sending up vertical shoots off some of the lateral branches. We're not sure why this is as it hasn't happened before but it's either a response to the large dose of manure they got a couple of months back or it's a maturity thing. It's mainly the Li's that are doing this. We initially started pruning these off but have since decided to leave them unless they are crossing over existing branches.

Frost

Jujubes are deciduous and when dormant are extremely tolerant of cold conditions. There are several reports of them surviving -20 celcius and below. Since the trees flower relatively late in the season they are rarely affected by frosts.

Li Jujube fruit fully ripe

Fruit Harvest

Unlike most fruit trees, Jujubes flower and fruit over a long period. The result is that the fruit ripening is staggered and doesn't happen all at the same time as it commonly would in say stone fruit where the entire crop lasts only a couple of weeks.

Fruit does not ripen if picked green. The earliest stage for picking is when the green turns to a pale yellow and the first red blotches appear. Fruit will continue to ripen until it is fully red (no blotches) but at this point it will last only a few days until it starts to shrivel as it enters the drying phase.

Jujube fruit ripening stages

Jujubes are precocious trees - they fruit very early in their life. Fruit will often appear on 1 year-old trees, although from experience we have found that leaving fruit on young trees will consume all their energy and retard their growth. For this reason we recommend removing fruit from immature trees in their first and second years - painful though it is. However you will reap the rewards in the 3rd year when the tree is larger, better established and carries a much larger crop.

Parrot damage to Jujube tree

Pests and Diseases

The only serious disease affecting the Jujube is Witches Broom disease however this only really prevalent in China and Korea and so not really a major concern outside of those countries unless you are considering importing stock.

Pests on the other hand vary by location. Parrots took a strong liking to our 2 year-old trees last year and very nearly ringbarked the lot until we had them netted. This poor fellow in the picture did actually survive but it was touch and go. If you live in Australia do not underestimate the destructive power of parrots - they may look cute but they love to chew things and man those beaks are sharp. Scarecrows and most other kinds of deterrents only work for a limited time. Netting is the only long term solution.

Australian Twenty-Eight parrots
Rabbits can also cause significant damage by gnawing at the bark around the base. In other countries burrowing animals can also be a problem such as Gophers in North America or Moles in Europe

User login