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21. 100 Trees Hole Plugs

THE easiest way to make the best tree hole is to backfill a tree hole dug to 600 mm min. with 20% bark chips from Bunnings. Fill tree hole with water to eliminate the “sink hole effect”. Then plant your tree a few days latter. Objective is to make a porous tree hole plug that encourages tap root development to access sub-soil moisture. Add more nutrient/top mulch as the tree develops as needed. Porous plugs are easier to water.  Think lateral and think like a tree. There are multiple recipes to make the best possible tree holes for all types of trees.

The soil beneath the canopy of a forest is a template for anyone planting trees. Forest soil is soft and aerated – full of organic vegetative matter (OVM) Suitable trees will grow there by themselves – unassisted by the hand of man.

If country has hardened from cultivation or overgrazing – it will usually have a hardpan – which is a layer of compacted dirt up to 400mm deep from the surface – a hardpan is deficient in OVM.

Loam is more susceptible to hard panning verses self-mulching cracking clay alluvium types of soil. All soil types will hardpan once organic vegetative matter is reduced or eliminated.

(1) GOOD NEWS! Once soil reaches 8% OVM it is difficult if not impossible to hardpan. OVM keeps particles of silt sand and clay apart by a process known as flocculation. Results on display here are based on charcoal as main tree hole plug material. BEST Tree Hole Plug material may vary = PREFERENCE now is for Wood Chips/Wood Shavings with 5 to 10% added biochar + manure/blood and bone (variable according to species) 

(2) Another excellent low cost tree hole plug medium is wood shavings (available as animal bedding from rural produce stores) blended with sheep manure and seaweed/fish pellets. Recently planted Jacaranda Trees have grown 4 fold in 8 weeks with this blend. (as of April 2021)  

(3) Recent planting Tipuanas into holes dug to 2 metres with a 300 mm auger in good black soil (with no added backfill nutrient just disturbed soil) – have grown up to 1.8 metres within 5 months   

(4) Dig tree holes to 600 mm minimum. This provides ease of access to sub-soil moisture. Prior to planting fill and soak the hole. It may take several days to absorb. Absorbtion is enhanced by life forms in the soil that aerate the subsoil – most important is the earth worm. 

Tree Hole Plugs can be managed to encourage tap root development. Only only apply small regular amounts of water direct into the plug – water then moves down through the porous plug to tap root. SAME METHOD used to establish GRAPES. Then after 1-2 years provide the seedling with a substantial soaking once or twice a year variable according to rainfall. 

100 Trees were planted Dec. 2016 to April 2017 into Sand Clay Duplex and Heavy Dark Alluvial Soil in 3 paddocks. Tree Holes were dug to 600 mm min. back filled with hardwood charcoal + liquid offal + soil. A tradesman’s wheelbarrow of charcoal was sufficient for every 4 trees. 100kg of wet animal offal was applied as 1000 litres of liquid fertiliser (for 100 tree holes). Another 20 litres per tree hole (of fresh water) was used to wash and settle soil into plug. This creates a settling effect (to avoid sink holes).  NOTE: Charcoal is suitable for SOME TREES but not ALL TREES.

Location: Janahn Forest, Jimbour. Q Australia. 190 km West of Noosa on The Western Fall of The Great Divide – 8 km East of Jimbour – part of The Condamine Flood Plain that Flows to Storm Boy Country in South Australia.

Words Explained

BioChar: Also known as charcoal. Best made from a single type of material. eg: (1) all hardwood or (2) all bone or (3) all softwood or (4) all bark. SEE STORY (29) Making BioChar Simple

Tree Hole Plug: Backfill of porous matter – made of (1) biochar (2) sawdust/bark chips (3) twigs and leaves (4) compost (5) sheep cattle manure = mixed with original soil taken out of same tree hole. Porous plugs provide for easier root development – tap roots can get down to access sub-soil moisture.

Humus: Soluble plant food derived from a ratio of 12 parts carbon to 1 part nitrogen. Excess carbon locks up nitrogen and makes it difficult for plants to absorb = result is yellowing of leaves. Excess nitrates can make plants weak and vulnerable to insect attacks. Mineral rich balanced humus provides for plants that are stronger and more tolerant to frost and heat.

Finding Humus Equilibrium: You can alter any soil PH to neutral by adding humus. Charcoal (which has no nitrogen) will increase alkalinity. Add nitrogen to the same charcoal and it will convert to humus over time. Hardwood sawdust has less nitrogen than softwood sawdust.

Protein contains nitrogen. Fats & Carbohydrates do not. Cellulose is a carbohydrate. Feathers are 80% protein. Flesh is maybe 40% protein. Leaves may be 12% to 28% protein. Trunks may be 3% protein. All living things have different levels of protein in different parts of the body.

If you backfill a tree hole plug with low nitrogen material – you need to add nitrogen. This is an acquired skill that one must master relevant to your own unique soil and climate.

Excess nitrogen can kill trees. Some trees are more susceptible than others – especially Hoop, Broad Leaf Bottle Trees and Wilga. All 100 Trees here were fed the same type of nutrient – all were planted at the same time in the same biochar plugs. (unless indicated otherwise in photo – some were planted before or after main planting)

SEAMUNGUS Fish and Seaweed Pellets is one low cost method of making your own liquid fertiliser verses buying liquid seaweed in a bottle.

PHOTO 1: ADD 1 kg of these pellets to 100 litres of water and start to dissolve by agitating. After one day take out 50 litres of now dark fish/seaweed liquid and apply to seedling trees. ADD 50 litres of fresh water to same fish/seaweed liquid and continue the process. It may take 200 litres of water to fully dissolve 1 kg of fish/seaweed pellets.

Applying Seamungus as liquid fertiliser is safe if done gradually. After first application – wait a few days – then apply pure water – then a few days later apply more Seamungus solution – repeat as needed until seedling leaves are dark green.

EXPERIMENT FIRST as excess nitrates will harm all plants – 1 KG of Pellets will safely feed about 10 seedlings. This liquid fertiliser method has been used with great success for recent Pecans & English Oak planted into BioChar Plugs.

OBJECTIVE is to add the right ratio of nitrogen to carbon that converts to humus and in doing so change the PH of the Bio-Char Plug to suit the seedling in its unique tree hole situation during establishment.

Results over last 4 years: In hindsight this mix of biochar and liquid offal was too rich for some trees – while Belah and Kurrajong thrived. Black Frost (more than minus 4) was the biggest adversity. Excess lush green growth was too fragile. Most trees recovered. BEST to reduce watering from Feb/March onwards to reduce green tips going into Winter. NOTE: Winter temperatures here fall to minus 7 degree Celsius. ALSO: since Cyclone Debbie of April 2017, we have had 2 x 10-month periods with NO EFFECTIVE Rainfall. Tree mortality was 15% and they have been replanted.

PHOTO 2: Crown of a Bunya Pine now forming two trunks. To date this Bunya has lost its crown at least 3 times to sheep – frost – heat. The tree itself remains intact. Provided the tree has ample water & is strong enough it will regrow. Date of Photo 01/01/21

100 Trees Hole Plugs

PHOTO 3: Same Bunya from Photo 2 was planted on a divot (shallow pan cut with a grader blade) in the saltbush paddock 6 years ago – now 1.5 metres tall – it has been “slow pruned” of its bottom lateral branches. Lateral branches are cut back to about half way. Maybe the following year they will be cut off at trunk – or simply allowed to fall off over time. Branches were pruned to lighten the tree to avoid potential wind damage. Intact half branches will reduce rubbing from animals. Date of Photo 01/01/21

100 Trees Hole Plugs

PHOTO 3a: This is a pruning method used for Belah, White Cedar, Silky Oak and Bunya (above photo). Lower lateral branches are half cut. Then the following year cut off close to trunk. Reason: Trees grow better? Part of strategy to get crown above grazing height of animals.

100 Trees Hole Plugs

PHOTO 4: Trees in guards in 10 metre grid formation will eventually provide all of this paddock with some shade for part of the day. All trees here are compatible with grasses. This is the alluvial soil section with heavy dark soil. Date of Photo 01/01/21

PHOTO 5: Replanted Bunya with single growth point – now 2 years in ground in sand/clay duplex soil. Date of Photo 01/01/21.

PHOTO 7: Same paddock as in Photo 4 + 8 with row of Bunya and Hoop. Stripes of grass were knocked down with a disc plough and then strips in between were burnt. SEE Photo 8 Below. After the big rain of Jan. 2020, the grass here was too tall and rank for sheep to handle. Now after 100 mm of December 2020 rain sheep will return to keep grass in check. Also: Tall Bambatsi Grass was starting to dominate in this paddock – it grows faster than native grasses – so by moving livestock in after rain we can lessen the Bambatsi dominance. With ample new green grass sheep will ignore the unprotected Bunya and Hoop. Date of Photo 01/01/21

PHOTO 8: Double row in sandy soil paddock. Bunya and Hoop to left with mix of White Cedar and Bottle Trees to right. White Cedar are growing faster here in lighter soil. Winter 2020 Strip of Trees on Fence is easier to protect with a single Electric Hot Wire when needed. Double row of is about 3 metres apart with every tree in both rows spaced at 10 metres.

100 Trees Hole Plugs

PHOTO 9: Best 4 year old White Cedar in heavy dark soil now 3 metres tall. Tree was adversely affected by a hail storm Oct 2018 – so it was pruned back – now in full strength and growth mode above grazing height of sheep and small cattle. Date of Photo 01/01/21

PHOTO 10: Tipuana takes time in this country due to extra cold Winters. For first few years they are base pruned every Spring until they are strong enough to grow about 1.5 metres over Summer – then cut off up higher at 1 metre – then new growth is cut back to 3-4 new branches as seen here. Biggest trees in the district are 10 metres tall on black soil without added water. Date of Photo 01/01/21

PHOTO 11: 12 year old Belah on light sandy soil in Saltbush Paddock planted originally next to a Saltbush. Date of Photo 01/011/21

PHOTO 12: Centre row of Belah and Saltbush was planted 12 years ago. Belah grows much slower in this poor sandy soil – they do gain vigour over time as they accumulate nutrients in their root system in association with mycorrhizal fungi. Date of Photo 01/01/21

PHOTO 13: This English Oak Seedling (inside a stock proof tree guard) was grown from several Acorns direct planted May 2020. Acorns require activation prior to planting – placed at depth to 100mm and covered with sand into a pre-dug and prepared 600mm deep tree. New seedlings emerge after the last frost. Only the strongest seedling will be allowed to grow. The advantage of direct sowing these trees from seed is extra root development – by mid-September roots may be 400mm deep into this biochar tree hole. Date of Photo: 01/12/20

PHOTO 14: 3 Year Old Black Mulberry – 2 metres tall -grown from cutting planted on a BioChar Burrow – pit of charcoal 2metres x 1 metre – 600 mm deep. Heavily pruned to slow growth – and shape tree for long term shape – above grazing height of sheep – Winter deciduous – cattle may then graze if desired. Date of Photo 01/01/21

PHOTO 15: 9-year-old Belah in Adgingbong Paddock with lateral branches cut off to 2 metres (above grazing height of small cattle) – this tree is about 5 metres tall. Date of Photo: Winter 2020

PHOTO 16: Roots of 7-month-old Kurrajongs – will grow best with a soft porous tree hole plug.


You encourage deep tap root development with small regular “drip irrigation” for first 12-24 months. You want the roots to follow the water down – so do not overwater with broad soaking initially if you want to encourage deeper tap root development.

2 x 9 litre watering cans with a rapid refill tub are the fastest method for hand watering on a regular basis. Tree holes when first dug will often hold water. Nutrient added to tree hole plugs will attract all types of micro life forms that will drill and aerate the hole.

Usually after a couple of years when extra water is trickled in – a tree hole it is capable of absorbing hundreds of litres of water – ever increasing as the expanding roots make the sub-soil softer and better suited for water absorption.

AS TREEs GROW they respond to occasional “big soaks”. Not unusual to see Bunya Pine grow 200 mm in a few weeks after 500 litres of trickle water applied to a developed tree hole (usually best in year 2-3 in hard frost areas)

20 litre bucket with small hole in base may be filled with water to function as a drip irrigator.

Yellow Leaves

Dark green leaves do not need feeding. Just add water. Yellow leaves are an indicator of nutrient deficiency or lack of water stress. Top up nutrients via liquid fertiliser or by sprinkling nutrient around the drip line – cover with mulch and water in. Best to keep nitrogen rich nutrients away from trunk – excess nitrates kill trees.

Livestock Movements

After 4 years of care and establishment 80% of these trees are stock safe for sheep and weaner cattle with no tree guards. Silky Oak + Tipuana are the only species that still need protection.

Why Shaded Forest Grazing

When these trees are full size on a 10-metre grid – all parts of the paddock will receive shade for part of the day – say average 30% over the course of a day. Same shade is dappled.

Trees restore the nutrient cycle by bringing up deep stored reserves of micro and macro nutrients from the sub-soil – which is excreted back to the top soil via leaf litter. Roots and leaf litter increase Organic Vegetative Matter aka humus which in turn feeds the pasture and the trees.

Climate Context

This is a 600 mm Rain Fall Zone where extended dry periods are common. Establishment time for all of these trees varies significantly according to soil type/rainfall.

Several key reasons for tree selection:

Silky Oak = One of the fastest growing trees – prefers lighter soil Belah = Fast growing in heavy clay soil Broad Leaf Bottle Trees = Fastest Growing Bottle Tree + Winter Deciduous Bunya + Hoop = Stock Safe Sooner White Cedar = Super Fast + Winter Deciduous + Grows in all Soils Kurrajong = Grows in all Soils + Tough Narrow Leaf Bottle Tree = Nice Tree PLUS THEY all GROW HERE naturally.

Making Charcoal AKA BioChar

Wood ash and charcoal increases PH towards alkalinity – so may potentially be counterproductive if applied excessively – unless neutralised with nitrogen.

Easy way to make biochar – you make a windrow of the same medium EG: Hardwood branches or Iron-Bark Bark for consistent burning. Start the fire at one end of windrow with water ready. As the windrow burns you rake away the coals and extinguish with a spray of water. A full ute load of dry timber branches may take about 1-3 hours to burn down. You need 1000 litres plus of water to extinguish.

PRACTISE FIRST with small pile. A full tradesman’s wheelbarrow of charcoal is then sufficient for about 4 tree holes (variable) with some spread and dug into top one square metres around tree base

ALL IS VARIABLE According to Type of Soil you are working with. Ultimately trees will grow out and away from original tree hole plug – initial work fast tracks the establishment of seedlings.

If you live in a high rainfall zone with rich volcanic soil you may be able to establish trees with minimal effort and simply plant the tree.

Everything explained here was developed to suit our unique environment. Adjust methods to suit your situation. Over time the plugs are absorbed and consumed so trees must match environment.

WOOD SHAVINGS and BARK CHIPS are READILY available and work well in conjunction with applied nitrogen base fertilisers

Sheep skins and cow hides are long term break down plug material – THINK LATERALLY – use whatever is economically suited for you and your environment.

Tree Guards:

All of trees will benefit from guards. Without tree guards this planting would have been extremely difficult – tree mortality would be substantial.

Low-cost Corflute Guards are one option.

PHOTO 17: 4 month old Pitaya Peruvian Apple Cactus available as Small Cactus in Plants PITAYA CACTUS 

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