Bees & Trees

Bees are an important part of our ecology. They are the main pollinators of many fruit and vegetable species, thus increasing yields. They also provide us with honey, and some medicinal products such as propolis and royal jelly. This Fact Sheet deals with what bees need, how the trees supply these needs, and how bees assist pollination.

What the bee needs

Pollen is the source of protein, minerals, fats, vitamins and trace elements in the bees diet. It is necessary for their growth at all times of year, but especially in spring and early summer when large numbers of young bees are being raised.

Nectar is a sweet liquid secreted by plant nectaries, which are usually located in flowers. It is composed almost entirely of sugars and water.

Propolis is a resinous material that bees usually collect from plant buds or scar tissue. For us, it has antiseptic properties, and is effective in preventing inflammation.

In the spring pollen is especially important for raising young bees.
In summer nectar from trees supplements the flow from main sources, eg clover.
In autumn nectar is stored to provide a food bank for the winter.
In winter nectar and pollen are needed for maintenance.

The needs of the bees differ according to the time of the year.
In the Pollen and nectar are stored in the hive when there is a surplus.
Shortages of nectar can be overcome by the beekeeper feeding cane sugar or honey to the bees, but it is not easy to obtain effective pollen substitutes, and in some areas of New Zealand pollen shortages can be a real problem.
Many noxious or nuisance weeds are useful pollen or nectar sources. Gorse, broom, blackberry, barberry and crack willow are all good for bees. However, there are substitutes.

Trees which satisfy these needs

The aim must be to provide food for the bee throughout as much of the year as possible. There are many useful sources of nectar and pollen, and this list is but a small selection of potential trees for bees. Look around your area to see what bees appreciate at different times of the year.

Wattles (eg Acacia baileyana or A. decurrens) are valuable pollen sources, from July to September and beyond. Acacia retinoides provide hardy shelter, flowering March to May.

Kotukutuku (Fuchsia excorticata). Nectar and pollen are freely secreted from August to December. The pollen is dark purple and crumbly.

Black Locust (Robinia pseudacacia). This is a nitrogen-fixer and provides ground-durable timber. In some countries it is a major nectar source.

Lemonwood (Pittosporum eugenioides). A great nectar- and pollen-bearing plant, from August to early November.

Five finger (Pseudopanax arboreus). This is a hardy, reliable provider of spring nectar. Scented.

Ngaio (Myopopum laetum). This is a useful shelter tree in coastal areas, producing pollen and nectar from September to early December, and also propolis from the gummy buds.

Putaputaweta (Carpodetus serratus). A good spring/summer source of nectar and pollen. Pretty foliage (marble leaf).

Pohutukawa, rata and southern rata (Metrosideros spp.). These have plentiful nectar to make distinctive white honey. Beautiful flowers.

Lacebark or ribbonwood (Hoheria sp.). Profuse and attractive late flowering.

Eucalypts (eg E. viminalis, ovata and gunnii). Very good for autumn nectar and pollen, appreciated by birds and bees. Coppice for firewood.

Willows (Salix). Willows are good in wet places. Most species flower during August and September. Male willows provide pollen, females provide nectar.

Salix medemii is a male shrub willow growing to about 10m, and is particularly useful for bees because it flowers earlier than many other species, and at a time when bee food is often in short supply. Pussy willow (S. discolor) also has decorative catkins, and crack willows (S. fragilis) are a good nectar and pollen source.

The following species of willow have been selected to provide a continuous sequence of flowering from mid-July until early April (at Palmerston North). Flowering times depend on weather conditions, latitude, and altitude, and may be some weeks earlier or later in other districts. However, the sequence of flowering times generally remain the same.

Multiple-use trees

Some trees provide not only honey, pollen and propolis, but also fruit and nuts, stock fodder, shade and shelter, firewood, etc. Here are the more common of these:

Tagasaste (Chamaecytisus palmensis) (tree lucerne). For fast-growing shelter, long-term nectar and pollen (mid-April to mid-November), firewood, first-class sheep fodder (especially in drought or pre-lambing), and to encourage birds.

Blackwood (Acacia melanoxylon). Spring pollen, excellent timber, will coppice.

Chestnut (Castanea sp.). Pollen, honey, honeydew, timber, nuts, coppicing.

Kohuhu (Pittosporum tenuifolium). Hardy shelter, night-scented, free producer of nectar (September to December), pollen.

Willows. As well as providing food for bees, some willows are useful for basket making:
220 S. viminalis ‘Gigantea’ Heavy canes, leaf rust susceptibility low to moderate, green bark.
606 S. triandra ‘Black Maul’ Heavier medium canes, brownish bark.
609 S. purpurea ‘Green Dicks’ Lighter medium canes, reddish-green bark.
621 S. purpurea ‘Nana’ Light canes, red bark.

Bees and pollination

The honey bee is particularly effective as a pollinating agent because its body is specially adapted for pollen collection and transfer. It is covered with branched hairs, and has pollen-collecting structures on the legs (the antenna cleaners and pollen baskets).

Honey bees live in densely populated colonies. Individuals specialise either as nectar gatherers or pollen gatherers and collect nectar or pollen from only one plant species on any trip from the hive. This ensures that pollen from one flower is not wasted by being transferred to flowers of another species.

Bees and the commercial horticulturalist

Advanced management techniques can be used to increase the efficiency of honey bee colonies for crop pollination, and they can be built up in strength and moved onto a crop in large numbers at the required time. Hives can also be removed from target crops when pollination is completed, to prevent them being poisoned by insecticides and to stop them interfering with other orchard or farm activities.

Each honey bee colony can perform a vast amount of work. In a pollination hive of 30,000 worker bees, about 12,000 will be foragers. To gather enough nectar to make 1kg of honey will involve the bees in a total of about 175,000 flights from the hive. When pollinating kiwifruit, for example, an individual bee will visit over 100 flowers in an hour.

A good pollinating hive consists of two brood boxes, containing 25,000-35,000 bees, or about a box and a half of bees. Single-box hives and nucleus hives are not adequate and are not worth moving into orchards for pollination.

The most effective pollinators in the hive are the pollen-collecting bees, and the stimulation to collect pollen comes mainly from the presence of unsealed brood.

A pollination hive should have at least the equivalent of six or seven frames of brood, mainly in the bottom box, and not more than one or two frames of pollen. At least the equivalent of three full-depth frames of honey should be in the hive for stores.

Moving bees to crops

Hives should not be moved into a crop until after pre-blossom insecticides have been applied and the waiting period is over. It is best to move them in at about the 10-20% blossom stage.

If they are shifted in earlier, many bees will become orientated to other food sources and may be slow to work the target crop when it comes into flower. If the hives are shifted in much later, some flowers will have finished their development without being pollinated.

Correct siting of the hives in the orchard is important, and can increase the amount of time the bees spend flying.

Bees fly when the air temperature is higher than about 10ºC and when the wind is less than about 25km/hr, so hives should be placed where they are sheltered from the prevailing winds and receive maximum sunlight, especially in the morning.

Hives should be shifted out from the crop at about the 90-95% flowering stage, and definitely before post-blossom insecticides are applied.

Hive requirements for particular crops

The number of honey bee colonies needed to pollinate an area of crop depends mainly on the nature of that crop and how attractive it is compared with other food sources within flying range (3-5km).

Each crop has its own characteristics that may make pollination easy or difficult. For instance kiwifruit produces a pollen which bees collect freely, but no nectar. The sugar concentration of pear nectar is often below the threshold of attractiveness for bees, and plum nectar is attractive but the weather is often bad when plum trees flower.

Hives per hectare. Here are some general recommendations for average conditions:
apple – 1-2
apricot – usually none used
avocado – 5-6
blackberry/boysenberry – 2
blackcurrant – 3-5
blueberry – at least 2
cherry – 0·5
citrus – varies
kiwifruit – 8
peach and nectarine – 0·5
pear – 0·5
plum – 0·5
raspberry – 1-1·5

For further information contact an apicultural or horticultural advisory officer.

Should you buy your own hives?

Many people become interested in bee-keeping through their involvement with horticulture and the need to pollinate crops. But there is no such thing as free pollination. Running your own hives simply to save the cost of renting hives at blossom time can be an expensive way of pollinating your crop. Think carefully about the following points.

• Bees in permanent hives have established flight paths to food sources, and may be slow to move on to the desired crop when it begins to flower. So the hives must be located off the property except at blossom time. This also minimises the risks of possible insecticide poisoning.
• Honey bee colonies must be managed intensively, especially during spring, to ensure that they are strong units at flowering time. Growers and farmers are often busy in spring, and so hive management may be neglected at a critical time.
• Many people who own hives mainly for free pollination lose interest in managing the bees, especially after a few episodes of bad stinging. This begins a vicious circle of less management leading to swarming and a more aggressive strain of bee, leading to even less interest in the hives, and so on.
• It often culminates in the hives being burnt because they have become diseased or simply neglected, but in the meantime the growers own crop has not been pollinated adequately. Diseased hives put at risk other hives brought in for pollination. If those hives become diseased, beekeepers are unlikely to return next year, and every orchardist or seed farmer suffers.

If you wish to use your own bees for pollinating crops, recognise that this requires specialised management, hard work, and a reduced honey crop and this is in no way free.

Willow cuttings

Bee willow and basket willow cuttings (25 cm long) can be purchased. Cuttings are usually dispatched from June to early September.

References

HortResearch Aokautere Research Centre, Palmerston North, provided the information on willows.
RS Walsh: Nectar and Pollen Sources of New Zealand (National Beekeepers Association.)
Andrew Matheson: Practical Beekeeping in New Zealand (revised edition).
George Stockley: Trees, Farms, and the New Zealand Landscape (Northern Southland Farm Forestry Association)
LJ Metcalf: The Cultivation of NZ Trees and Shrubs (Reed Methuen)

This Fact Sheet was first printed 1988 and updated 1991.
Updated again 1996, by Peter Syms & Maurice Denton.
Privacy removals and proprietory format conversion – December 2007

This fact sheet was produced with the latest information available at the time of publication. This sheet should not be considered the ultimate in information for New Zealand growing conditions: it is just a basic guide on the subject. If any member has information to add, or feels that any of the information is misleading, then we ask you to use the contact below.