Edible Forest Gardening 101: Pollination

One of my many forays into the wonderful world of retail was working at a garden centre, as a “trees and shrub sales associate.” It was a crash course in memorising pertinent information on plants, in order to best advise the customers.

For example, in selling plants in the genus Prunus (plums, cherries, almonds, peaches, nectarines, bird cherries, sloe, and others), this meant closing my eyes and picturing a chart on cross-pollination every time I informed a customer they couldn’t purchase a single tree, and still expect fruit.

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Bron & Sons Nursery Co. Pollination Chart

Many (but not all) Prunus are “self-incompatible,” in that they need to be pollinated by a different, but closely related species, subspecies, cultivar, or variety. This is because when it comes to fruit trees, “cultivar” usually means that all trees sold with a particular name are clones of a single plant.

In the garden centre, we often got around this by selling trees that were grafted with 4-5 different compatible species/subspecies/cultivars/varieties, like the “tree of 40 fruit.”

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The picture of optimal pollination is further complicated by the fact that blooming times have to overlap significantly in order to guarantee a fruit set: fruit trees often have a window for best fertilisation that is smaller than the window in which blooms are open. 

Different plants in the Prunus genus, for example, have different seasonal windows in which they bloom, and despite attempts to chart and match trees with “pollination partners,” factors like the rootstock onto which a tree is grafted, or the microclimate in which it is planted can also alter flowering time.

Beyond that, there are genetic restrictions on which trees can successfully share reproductive material with each other, but they are full of exceptions. Take the Prunus example again:

“European plums (Prunus domestica [itself a hybrid species, likely descended from be Prunus spinosa and Prunus cerasifera]) can inter-pollinate with closely-related species such as damsons (Prunus domestica subsp. insititia), mirabelles (Prunus domestica subsp. syriaca) and cherry plums (Prunus cerasifera). European plums cannot generally cross-pollinate with Japanese plums (Prunus salicina). Sweet cherries (Prunus avium) and Acid cherries (Prunus cerasus) are also different species but can potentially cross-pollinate each other.”

     -  Orange Pippin Fruit Trees

Prunus avium is thought to be one of the parent species of Prunus cerasus (sour cherry) by way of ancient crosses between it and Prunus fruticosa (dwarf cherry) in the areas where the two species overlap. All three species can breed with each other.

     -  Prunus avium wiki

Pure wild plums – Prunus nigra and Prunus americana – are by far the best pollinizers for hybrid plums. 

     -  Plums on the Prairies

Peaches, nectarines, and almonds can all cross-pollinate as well: indeed, I have an almond tree that I originally thought was really a hybrid between an almond and a peach, which is a common hybrid made to create better rootstock for both almonds and peaches/nectarines.

Almonds are the seeds inside of peach-like fruits: it’s easy to see their genetic closeness.

There are a tonne of charts and online databases that can be used to look up the genetic and pollination relationships between fruiting trees, shrubs, and vines, but in general, good planning is essential in terms of choosing trees for a forest garden. Otherwise, you may get nothing but flowers!

I tend to think of the pollination relationships between plants as almost social: the forest garden is like a party where everyone is arriving and leaving at different times, and everyone has different—but extremely specific—genders, sexes, sexual preferences, and orientations.

My persimmon trees and kiwi vines are dioecious, for example, meaning male and female flowers are on different plants: a minimum of two plants are then required to produce fruit. 

Persimmon Flowers

My Prunus (Stone Fruit), Pyrus (Pear), and Malus (Apple) trees have both male and female parts (”perfect” or hermaphriditic flowers, botanically-speaking), but usually need to get a little strange cultivar-wise, and sometimes (rarely), the latter two genera trade pollen between each other. My Chaenomeles/Cydonia (Quince) are generally happy on their own, but can occasionally swap gametes with closely-related pears.

If you would like to avoid all of this hassle, research, and planning, look for trees and shrubs that are “self-fruitful” (not just “self-pollinating”).

Self-fruitful plants (and clones) set a crop of fruit after self-pollination; some of these plants bear fruit with no seeds (parthenocarpy); others develop seeds with embryos that are genetically identical to the parent plant (apomixis); and others produce haploid seeds that develop from an unfertilized egg cell. (When haploid seeds germinate they are very weak seedlings with only half the chromosomes of normal seedlings.) Regarding temperate zone tree fruits, self-pollination and fruit set does not mean self-fertility and the development of normal seeds.  

    -  Plums on the Prairies

There are so many complex relationships, and they are far from being 100% clear in the scientific record: orchards usually have a pretty good handle on this sort of thing in that there are tried-and-true combinations that are used for optimal pollination, but there is always room for experimentation, and “rules” with regards to plant genetics are plastic and ever-shifting.

Generally, my advice in handling this is the same as it always is: plant lots of trees, plant with redundancy, and plant genetically diverse species!

#tree planting #forest gardening #edible landscaping

There’s been a bit of a production line in the kitchen today, preparing various homemade produce to give as Christmas presents. I dusted off and properly labelled some jam and chutney made in the summer and strained the fruit off the damson and sloe vodkas and put them in nice bottles. I also made a batch of blackcurrant jam from some fruit I froze when I didn’t have time to deal with the 12lbs of fruit I picked in one afternoon in July. Another delayed project is some rosehip syrup - the defrosted fruit is bubbling on the stove ready to strain through a jelly bag overnight and boil up with sugar tomorrow.
This Tree Is Growing 40 Different Kinds Of Fruit At Once

This single (and quite colorfully blossoming) tree grows 40 different varieties of peaches, plums, apricots, nectarines, cherries, and even almonds — but just how does it do it?

The making of a “Fruit Salad Tree”: Prunus Edition

I have several Prunus trees growing in my young food forest garden, but as I walk about in the neighbourhood and in plant nurseries, I often think “I could never conceivably plant all of the trees I would like to plant.” There are over 430 species in this genus, and countless cultivars: including almonds, peaches, plums, cherries, apricots, sloe, bird cherries, and nectarines – all those sickly sweet things with a stone in the middle.

Mirabelle plums are endemic to the wetlands around where I live, being re-seeded prolifically by birds. I know by observing them in my biome that they tolerate the Danish wet, cold, coastal climate. Thus, they are a natural choice for a hardy, disease-resistant rootstock. Finding the right Prunus rootstock for your biome means engaging in similar observation and experimentation: what are your local species? How do they tolerate your climate? Are they compatible with cultivated members of the genus?

My next step is to go around and ask the neighbours for scion wood from their Prunus trees, or deftly slip broken branches in my pocket when I am at the greenhouse (I’m on a budget, after all). These can be grafted on to the Mirabelle rootstock, and, pending compatibility and the strength of the graft, produce their unique fruits on one branch. Prunus species cross-pollinate each other, bloom at different times, and have an array of different blossom colours, meaning such a “fruit salad tree” will have bigger, more vigorous fruit, a longer blooming period, and a number of different colours.

Similar trees can be accomplished by grafting members of the Citrus genus (oranges, lemons, grapefruits, limes, tangerines, citrons, etc.), the Malus genus (apples, crabapples), or between the Cydonia and Pyrus genera (quince and pears).

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A citrus fruit salad tree

In theory, you really only need four trees, and you can cultivate hundreds of species of fruit in your own backyard!

To get started, here is a “Grafting 101” tutorial. May this inspire you to great Frankentrees of your own!

Blackthorn, William Morris & The Devil

“Early practitioners of dark witchcraft favoured the wood cut from Blackthorn and tipped with the thorns as a wand – or even as a ‘blasting rod’ or ‘black rod’, used apparently for cursing.  The rod would frequently have the ancient Futhark rune for thorn ‘Thurisaz’ scratched or burned into it.

The thorns have been found stuck into witches ‘poppets’, used as pins. Superstition tells us that the devil pricked the fingers of his victims with a sloe thorn and sealed the deals he made in the resulting blood.  Because a scratch from the sloe bush was apt to go septic if unattended, it was thought to be poisonous.Witches burned as heretics were sometimes accompanied into the fire with their blackthorn wands or staffs, and branches of it were thrown in to feed the flames. This may be where the tree gained its reputation for purification, and even exorcism.

The starry blossoms were considered unlucky and not worn as a decoration or brought into the house. They were associated with death, probably because they bloom on the bare, thorny black branches at winter’s end”

“The Blackthorn is depicted in many fairytales throughout Europe as a tree of ill omen. Called Straif in the Ogham, this tree has the most sinister reputation in Celtic tree lore. The English word “strife” is said to derive from this Celtic word. To Witches, it often represents the dark side of the Craft. It is a sacred tree to the Dark, or Crone aspect of the Triple Goddess, and represents the Waning and Dark Moons. Blackthorn is known as “the increaser and keeper of dark secrets”. The tree is linked with warfare, wounding and death, associated with the Cailleach - the Crone of Death, and the Irish Morrigan. Winter begins when the Cailleach (also the Goddess of Winter) strikes the ground with her Blackthorn staff”

“The Blackthorn has a long and often sinister history, associated with witchcraft and murder, but it is also associated with the concept of the cycle of life and death and protection not to mention its practical physical uses. It is often associated with darkness, winter, and the waning or dark moon, a particularly cold spring is referred to as ‘a Blackthorn winter’. The devil was said to prick the fingers of his followers with Blackthorn to seal their pact. It is considered the opposite of the benign Hawthorn (which is also known as Whitethorn) with which it so frequently grows. The Blackthorns spines are extremely hard and can cause a great deal of bleeding, and the wound will often turn septic. They were frequently used as pins by English witches and became known as the ‘pin of slumber’. The shrub was denounced as a witch’s tool by the church and therefore the wood of the Blackthorn was used for the pyres of witches and heretics. They were also placed under horse’s saddles, by the rider’s enemies, causing the horse to throw its rider when the spines pieced the horses flesh, causing injury or death to the unfortunate rider.

The Blackthorn is also seen as a protective tree and representative of the endless cycle of life and death. For all its deadly associations the blossoms were used in ancient fertility rites as well as being hung in the bedchamber of a bride on her wedding night. It provides blossom whilst there is still snow on the ground while everything else still seems dead from its winter sleep, its dense branches protect the year’s new chicks from predation and in their adulthood provides them with food when many other species of plant have lost their berries. It is a thicket of these trees that protects sleeping beauty in her castle, and witches in northern England would carve the symbol for thorn on a Blackthorn staff for protection.

The tree itself is said to be protected by the fairy folk. It is considered a fairy tree and is protected by the Lunantishee, a type of fairy that inhabits it. They will not allow a mortal to cut Blackthorn on May 11th or Nov 11th (said to have been the original dates of Beltaine (May Day) and Samhain (All Hallows Eve) before the calendar was changed. Great misfortune will befall anyone who ignores this advice. The Lunantishee may also be the Leannán Sidhe or Fairy Lover”