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Grow native trees from seed, pre-treatment and sowing tips.


 
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James Kilkelly
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PostPosted: Sun Sep 07, 2008 8:02 pm    Post subject: Grow native trees from seed, pre-treatment and sowing tips. Reply with quote

Grow native trees from seed, pre-treatment and sowing tips.
by GPI

I recently visited a house where the owner's youngest boy had grown a Horse chestnut seedling from a conker collected the previous autumn. The child plonked this healthy looking pot grown specimen in front of me, then he stepped back, arms folded, to receive the praise that was due to him. It was really heart warming to see this young gardener starting a tree from scratch, during these days of instant garden makeovers where the installation of semi-mature trees into the landscape are all the rage.

Starting a tree from a seed can be one of the most rewarding gardening activities you can undertake, as you and you alone will be responsible for the eventual mature tree. No middleman, no nurseryman, just you, the seed and the soil.

Saving seedlings.
You may not even need to sow a seed as lots of recently sprouted trees seedlings can often be found growing in the soil at the base of mature trees. You would be amazed at how many native Irish trees freely self-seed.

An example of a self seeded oak seedling growing inside a beech tree hollow, photo / picture / image.

I know one particularly resourceful gardener who when he goes walking in any woodlands, forests or parklands, always brings a small, foldable trenching shovel and a plastic bag with him. If he comes across a small seedling, he digs it up, bags it and then plants it at home.

I must emphasise that he does not rip up newly planted trees from public parks or private property and he always makes good the patch where the young trees were growing. So if you don't mind getting lots of smaller trees for free, that's one method you could follow.

Seeds easy?
If you are not one for carrying a shovel around with you, then collecting tree seeds and sowing them at home may instead be the way to go. Now even though tree seeds have sprouted and grown to maturity for a long time before they had help from us humans, there are a few tree types that may need an extra little bit of encouragement from us in the form of pre-treatment.

At the easy end of the scale requiring no significant pre-treatment before sowing are acorns, the quick sprouting seeds of the oak. Whereas at the other end of the scale, you have the seed of the hawthorn which experiences a double dormancy requiring pre-treatment plus several seasons to germinate, not to mention the fact that you will also have to extract the seed from its fleshy coating before beginning.

If you are looking to source tree seeds you may be able to find some here.... Tree seeds



Pre-treatment of seeds.
Whether your tree seeds grow will depend as much on the pre-treatment before sowing as the way in which you sow them. Pre-treatment of your seed will allow you to bypass or at least speed up the seeds in built dormancy.

You see, Mother Nature has installed this dormancy in many tree seeds to prevent them germinating if the environmental conditions are just not right during the normal germination period. Dormancy ensures a percentage of seeds will germinate at some time later when the conditions for growth are much improved, thus ensuring the species' survival.

The two main types of tree seed pre-treatment carried out by the canny gardener are scarification (penetrating the seeds outer coating) and stratification, which is commonly exposing the seeds to a spell of cold similar to that experienced during winter.

Scarification.
The true definition of scarification relates to the roughening or chipping of the seeds outer coat, so that it will absorb moisture better, promoting growth. But this is only carried out in the case of extremely hard coated seeds, of which we have no real examples among our natives.

However, a few native tree seeds will benefit from soaking in water to soften their hard outer coats and leech away the chemicals that may inhibit germination. You can quite easily cover the seeds for two days in clean, cold water by initially placing them in a sock or an old pair of tights tied at the top.

You can then submerge this within a water container containing three or four times the seeds volume of water. It is worth changing this water after the first day to prevent a build up of chemicals.

After soaking, allow the surface of the seeds to air dry by hanging the sock/tights on the washing line for a few hours. Alternatively, if you feel up to it, you can swing the seed "bag" around your head like a lunatic for a while to dry it out.

The only Irish native trees that require this cold-water treatment before sowing are alder, ash, birch, juniper, yew and beech (not truly native, naturalised). Our native furze or gorse seeds need a similar treatment to breach its hard seed coat, but with one small change. The first soaking must begin with boiling water, so don't forget to use a heatproof container if pre-treating the furze.

Cold water treatment..... Alder, ash, birch, juniper, yew, and beech.
Hot water treatment..... Gorse/furze.

An example of a our native furze or gorse, whose seeds need the hot water treatment, photo / picture / image.

Stratification.
Stratification is basically exposing certain seeds to a spell of cold similar to that experienced during winter, this break dormancy and greatly improves evenness of germination. In the case of shallowly dormant species, alder, birch, Scots pine and beech, this can be done at speed in the section of your kitchen fridge, which is below 5°C.

The process is simple enough to carry out once you have a few materials to hand. Firstly, get yourself a bag of plain moss peat (no added fertilisers etc.), and a bag of horticultural sand. Sharp builders sand or vermiculite can be used if horticultural sand is unavailable.

Mix these up, one part seed, one part peat, and one part sand. Avoid using dry peat; ideally it should be dampened down before mixing to a point where if you squeeze a clump of it, you just about produce one or two drops of water.

Fill the seed mixture into plastic bags, loosely tie, and place in the vegetable compartment of the fridge (not the freezer). Alder, birch, and Scots pine will need four weeks chilling, beech will need six to eight weeks, whereas crab apple and beech will need ten to fourteen weeks.

Shake the bag weekly whilst checking for signs of rotted seeds to remove or growing seeds, which should be immediately sown into pots or open soil if they happen to germinate in the bag. If by the allotted times mentioned above, nothing has germinated, take the individual seeds from the bag then go ahead and sow them.

Fridge treatment...... Alder, birch, Scots pine, beech, and crab apple.

Deeply dormant tree seeds
So the fridge pre-treatment of certain tree seeds allows you to bypass or at least speed up the seeds in built dormancy, thus avoiding years of waiting and disappointing failures. However there are certain Irish tree seeds that tend to break the heart and patience of gardeners when they fail to grow year-in-year-out. These are the deeply dormant seeds, incapable of sprouting under any conditions unless pre-treated for a relatively long period of time, which in the case of holly can be anything up to 75 weeks.

Don't worry though, you won't have bags of seeds cluttering up your refrigerator while they chill for a year or more, as the dormancy of these seeds is ideally broken in the great outdoors. Some need cold temperatures only (4°C and lower), others need warm (15°C and higher) followed by cold, but no matter what they require they will receive it outdoors, given enough time. So, if you want to grow trees the likes of ash and rowan, here is how to pre-treat these deeply dormant individuals.

Hazelnuts require outdoor pre-treatment, photo / picture / image.

Outdoor containers.
You will need a free-draining container(s) of some sort; this could be anything from old plant pots to barrels cut in half. Even dustbins, tubs, and large buckets can be used, provided these containers have adequate drainage holes created in the bottom.

Add to the containers drainage further by spreading in its base a 5-10cm deep layer of polystyrene packaging broken up to golf ball-sized chunks. No polystyrene packaging, you can also use a layer of stones or broken terracotta, however this is added weight anytime you have to move the container. Whatever drainage crocks you use you should cover these with a 2-3cm layer of sharp horticultural sand to prevent any compost washing down to block the drainage holes.

Now mix your deeply dormant seeds into plain moss peat (no added fertilisers etc.) combined with horticultural sand. Mix these up, one part seed, and one part peat, with one part sand.

Avoid using dry peat; ideally it should be dampened down before mixing to a point where if you squeeze a clump of it, you just about produce one or two drops of water. Sharp builders sand, perlite or vermiculite can be used if horticultural sand is unavailable.

All mixed, now layer your seed/compost on top of the previously created drainage layer within the pots. Seal all of this with another 2-3cm layer of sharp horticultural sand atop the container before finally moving it to a sheltered and shady spot outdoors, such as next to a north-facing wall. The container will remain in this location for quite a while; so don't forget to label it with the name of the individual tree seeds it contains.

How long to pre-treat your deeply dormant tree seeds.
How long the pot remains in this location depends entirely on the seeds it contains, for example ash seeds need at least a years outdoors pre-treatment including a full summer for its embryo to grow. So the seed should be ready for sowing the second march after collection/pre-treatment.

Others for removing from the pre-treatment containers then sowing the second march are yew, hawthorn, holly and the dog rose (Rosa canina), a shrub, but one of our native nonetheless. The tree seeds that just require one winter chilling followed by sowing the following march include elderberry guelder rose (Viburnum opulus), rowan/mountain ash, whitebeam, bird cherry/wild cherry, juniper, hazel and blackthorn.

Remember that while you are pre-treating your seeds in containers over the weeks and months, you should water the mix if it shows signs of drying out. Neglecting this and allowing the seeds to dry out will result in poor germination down the line.

Also be aware that seeds, especially those that are nut-like (hazel etc.) should be protected against foraging mice and birds. A simple solution to this is to use galvanised metal mesh with very small gaps to cover your containers, mesh similar to the builder's diamond mesh that is often used in plastering jobs is very suitable for this purpose. All this being well, you must now be patient, and bide your time until your seeds are ripe for sowing.

Outdoor treatment...... Ash, yew, hawthorn, holly, dog rose (Rosa canina), elderberry, guelder rose, rowan/mountain ash, whitebeam, bird cherry/wild cherry, juniper, yew, hazel and blackthorn.

Sowing the seed, one method
When it comes to sowing Irish tree seeds there are two methods that are commonly employed. For large sized sowing projects, lengthy seedbeds are created in areas of cultivated weed free soil allowing the gardener to broadcast or scatter seeds on a grand scale. Of course growing on a grand scale can bring with it grand scale problems such as maintaining a weed free growing area, plus the constant catering to the water or fertiliser needs of legions of seedlings.

Instead, you can opt to grow a small scale by sowing your tree seeds directly into containers during March-April where they can be grown on until they are ready for planting out. This is a rewarding and low-pressure operation and thankfully so, especially if you intend to use tree growing as a nature lesson for your youngsters. This is the method I would favour to show the link between seeds and trees, so lets have a look at how you would tackle it.

What you need.
You will need some containers with volumes in the range of one to two litres, such as the black plants pots commonly discarded after planting projects. You can even grow your young trees in cut-off milk cartons of either the plastic or cardboard type, however be aware that the cardboard pots tend to become quite weakened after about a year. Whatever you choose, the most import factor in your pot is its ability to drain freely, so a few drainage holes should be created if none already exist.

You should ideally fill your container with John Innes seed compost; this soil-based compost contains grit for drainage and sufficient nutrients for early seedling development. Loosely fill your container with the moist compost to about half an inch from the top, then level and settle the medium by gently shaking or tapping the container.

To grow a horse chestnut you require just one conker per pot, photo / picture / image.

Next you will press your native tree seeds into the surface of the compost, the quantities of which vary slightly according to the native tree. In the case of wych elm, guelder rose, elderberry, dog rose, alder, and birch, you can sow five seeds per one litre pot. Wild/bird cherry, Scots pine, yew, whitebeam, rowan/mountain ash, juniper, hawthorn, beech, crab apple, ash, and blackthorn are sown thinner at three per pot, with holly, horse chestnut (not native) hazel, and oak the thinnest at one seed per pot.

Cover the seed thinly with about 5mm of horticultural sand or grit and the firm the pots contents by pressing lightly with a flat piece of wood. It is important that you do not cover the seed too thickly as this could prevent germination, this is especially important in the case of birch seed, so I tend to only cover it with 2mm of sand or grit.

From seed to seedling.
Stand your pots in a shady, sheltered spot outside and water from the top, keeping them moist at all times until the seedlings emerge. Once the seedlings emerge, move them to an area that provides shelter and plenty of light such an enclosed southwesterly facing area, a windowsill or polytunnel. Good light will prevent them from growing weak and spindly.

With many of the tree species you will have sown more than one seed in each pot, so remove all but the strongest seedling, transplanting any that you have extra pots for. Just like the seeds, never let the young seedlings dry out; their soil should be moist at all times but not saturated. To feed the young growing trees you can apply a liquid feed about once a month from April to July.

With this regular watering and feeding your young tree should not suffer from serious pests or diseases, and quite quickly reach 40-50cm tall. At this height it can be planted into its new home in your garden. If it fails to reach that height within the year it can be left in the pot (or repotted) for another year.

Now, even when you provide all the required pre-treatments and care, some of your seeds may fail to grow. But don't give up hope that quickly, as they might still only be dormant. Leave the ungerminated seeds in their pots and give them another year or two in court, they may just surprise you.

For guaranteed satisfaction, the easiest tree seeds for adults and children to grow are hazelnuts, acorns from the oak, and conkers from the horse chestnut. These seeds are not dormant so they can and should be sown straight after collection in autumn, so keep your eyes peeled for these beneath trees.
Once you get your hazelnuts, acorns and conkers home, you should throw them into a bucket of water. Those that sink have a much better chance of growing, whereas those that float are usually dead seeds, not worth wasting your time with. When throwing in your hazelnuts and acorns remove their buoyant husks and caps first to insure your "sink" test is accurate.


Associated content.....

Native Irish Trees --- List of Trees Native to Ireland plus information.

Native Irish Shrubs --- List of Shrubs Native to Ireland plus information.

Any queries or comments on Grow native trees from seed, pre-treatment and sowing tips, please post below.

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Last edited by James Kilkelly on Tue Nov 09, 2010 12:00 am; edited 1 time in total
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PostPosted: Mon Jan 04, 2010 11:54 am    Post subject: should I plant spanish broom? Reply with quote

I was on an Australian or New Zealand blog lately and found that some of the invasive species mentioned also noted Spanish broom should be eradicated. Sometimes what is a problem in one country soon becomes a similar problem in another. Maybe they're ahead of the curve. I put in clippings of the broom along the peaty area to fend off weeds coming over the fence. The broom apparently self seeds too much and can take over everything if conditions are optimal. Should I tear it up?
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PostPosted: Mon Jan 04, 2010 2:57 pm    Post subject: Re: should I plant spanish broom? Reply with quote

I should think you would be ok to leave them ormondsview.
If it is true Spanish broom (Spartium junceum) you may find that it struggles in a peaty soil if poorly drained.
It prefers sandy soil to grow in as well as self seed in.

Here are the commonly believed best conditions for Spanish broom seed germination......

Chip and soak seed, then sow at 21C/70F into average, well-drained soil.
The seeds prefers sandy soil and tolerate alkaline soils.
Good light. Zone 7-10

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PostPosted: Mon Nov 08, 2010 8:47 pm    Post subject: Re: Grow native trees from seed, pre-treatment and sowing ti Reply with quote

James Kilkelly, was GPI. wrote:
Others for removing from the pre-treatment containers then sowing the second march are yew, hawthorn, holly and the dog rose (Rosa canina), a shrub, but one of our native nonetheless. The tree seeds that just require one winter chilling followed by sowing the following march include elderberry guelder rose (Viburnum opulus), rowan/mountain ash, whitebeam, bird cherry/wild cherry, juniper, yew, hazel and blackthorn.

yew is mentioned in both the first spring and second spring group - just wondering if it's a single spring one?
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James Kilkelly
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PostPosted: Mon Nov 08, 2010 11:59 pm    Post subject: Reply with quote

Thanks for spotting this typo
Yew are part of the deeply dormant group so require removing from the pre-treatment containers then sowing the second march.
Original article amended.

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PostPosted: Tue Nov 09, 2010 11:18 pm    Post subject: Reply with quote

growing trees from seed very good read thank you ,I"ve still got my spindle berry seeds and should think I can get some degree of success with them after reading throughthis article ,fingers crossed !
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PostPosted: Wed Sep 26, 2012 1:05 am    Post subject: Reply with quote

when is the best time of the year to collect seeds from the furze tress ??
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