Planting seedlings for revegetation

Advice on planting native seedlings as part of a revegetation project.

About planting with seedlings

Transplanting seedlings as tubestock is more expensive and more labour intensive than direct seeding. However, there are some situations where seedlings will provide a better result.

For revegetation projects aimed at providing a windbreak or screening, planting seedlings gives you more control over plant density and design. 

In sensitive areas with limited access for direct seeding machines, for example riparian areas, revegetation works are best done with low-impact seedling transplanting methods.

Preparing the seedlings for planting

Soak your plants well, just before planting. This will make removing them from their containers easier and will hydrate the root ball before it goes in the ground, giving it the best possible start.

Planting in winter can raise the issue of frost damage. The most difficult situations arise in hollows, such as drainage lines, that collect cold air. These areas can be several degrees cooler than normal landscape temperatures (0°C on your verandah could be -6 °C along your creek line). In some areas, frost can kill seedlings out right.

To mitigate potential frost damage, plants should be ‘hardened off’. Nursery conditions are generally warmer than the paddock that the seedlings are destined for.

To harden plants off, place them for several days in an environment similar to the planting area, under cover at first, then out in the open.

In practice, hardening off is a difficult process as temperatures can remain mild for several weeks then dramatically crash when a severe cold front comes through. If you are planting in late autumn through winter when frosts are likely and you have just picked up your seedlings, you may need to force-harden the plants.

To do this, check the seedlings for soft, fresh growth. This growth is smaller and a different colour than the more developed leaves. Fresh growth drives plant activity pulling extra water through the plant, but it makes the plant very susceptible to frost damage and increases the plants transpiration (water use) rate. 

If your plants have new growth tips, take a pair of sharp garden shears and prune the top 25 per cent of the foliage. This reduces the plant’s water needs (transpiration rate), reducing demands on its root system and rebalancing the foliage to root mass.  

These yellow box seedlings have too much foliage for their root ball size. Once the plant experiences anything other than its usual nursery conditions, it will be placed under stress and have to drop leaves to compensate. 

Pruning by 25% may look harsh, but it will not harm the plant and greatly improves survival rates. Pruning reduces the likelihood of frost damage. The soft, fragile leaves are removed and the older leaves remain. The older leaves have more robust cells and the reduced moisture flow through the plant reduces the volume of water that can freeze and expand.

Seedling planting methods

Any method that successfully positions seedlings in close contact with the soil can be used to get your plants in the ground.

Regardless of the method you use, make sure you plant the root ball deep into the soil, preferably with 5 cm or more of soil over the top of the ball. 

Good root-ball-to-soil contact:

• insulates the root ball from the sun and wind
• gives the roots immediate access to moisture deep in the soil profile. 

Having some of the leaves and stem under the soil will not harm the plant, just ensure the majority of the plants leaves are out and able to photosynthesise.

A good soil moisture profile and soil preparation improves success. Soil that is cloddy and full of air pockets makes it difficult for the roots to break out from the ball.

Even though the surface of the soil is already drying, the seedling will be able to survive for many weeks on this deep soil moisture.  

Mechanical planting

Customised tree planting trailers, such as the Youman tree planter, which can be towed behind a vehicle on a three-point linkage, are used for large-scale revegetation projects, with varying rates of success. These machines have a single tyne at the front to rip the centreline.

A person is seated behind the tyne, with racks on either side of them to hold seedling trays. This person places a seedling down into the prepared soil as they are moving along, in between two press wheels that firm down the soil either side of the seedling and hold it in place. 

Operators need to be mindful of the safety hazards associated with this planting technique.

Mechanical planting is time-efficient and can work well in well-prepared loam and clay loam soils. In some cases, particularly on heavier soils, this method does not create a friable bed for the seedling to be planted in to and leaves too much air around the roots, stressing the plant and resulting in lower planting success rates. This can be partially resolved by having someone follow the planter, to firm down the soil around the plant but this will add to the time and labour required.

Manual planting

In general, hand planting methods are the most effective ways to plant your seedlings, giving you the greatest survival rate of plants.

Hand planting may seem time and labour intensive but it can be a faster job than you think. Getting it right in the first instance will also save you time in the long run, especially if it means you won’t have to replace plant losses.

Pottiputki, Hamilton tree planters and spades are all effective planting tools to assist manual tree planting, when used properly in well prepared soil. 

Planting using a Pottiputki

Developed in Finland, the Pottiputki is ergonomic and efficient for large-scale revegetation.

Benefits:

• No need to bend down.
• Can carry up to 100 plants at once.
• Allows planting at walking pace.

Limitations:

• Works best in soft soil.
• The Pottiputki’s planting tube struggles to cope with large plants. The largest 75 mm planter can handle tubestock, however, any plant that is bushy or growing at an angle can easily get stuck inside the planting tube. Some people also find the 75 mm planter too heavy to use for extended periods of time.

Step by step planting with a pottiputki

1. Prepare the planting zone. For example, with a multi-tine agri-plough followed by a rotary hoe to produce a friable planting bed.
2. Drop the seedling down the planting tube with the planting beak in a closed position.
3. Drive the planter deep into the soil and open the planting beak using the foot lever.
4. Remove the planter using a twisting action, leaving the seedling positioned in the planting hole.
5. Use your boot to push soil into the planting hole from both sides of the seedling.
6. Firm down the soil by pressing on either side of the seedlings with your feet and then move off to the next plant!

Setting up a planting station where the planters can re-fill their trays works well. Be careful that your planting design doesn’t get overlooked in a flurry of activity—plants are easily put in the wrong spot, which is a nuisance to fix.

Planting using a Hamilton tree planter

Australian-designed, the Hamilton planter removes a soil core to create a planting hole. It is ideal for compacted or variable soils.

In soft soil, the Hamilton tree planter can be used using the same principles as a Pottiputki. Create a hole with the planter then lower the seedling and back fill with your feet.

The robust Hamilton tree planter allows you to put your full body weight into creating a planting hole.

Step by step planting with a Hamilton planter

1. Drive the planter to full depth by placing your weight on the stepping platform.
2. The soil is removed with the planter. There is no need to empty the tool
3. The core from the previous hole is pushed out into the next planting spot.
4. The seedling is placed into the hole. Plant deeply to ensure good insulation of the root ball. It doesn’t matter that a few leaves are under the soil.
5. Fill in the hole with soil and firm around the plant. 

Using tree guards to protect your seedlings

Tree guards protect young plants but add cost in both materials and labour.

There are some minor benefits to guards. They can:

• Make seedlings easier to locate.
• Provide limited protection from herbicide drift.

However, for most farm-scale projects, it’s more cost-effective to manage pests directly rather than guard every plant.

Plastic tree guards

Plastic guards are durable but expensive. They can cause environmental issues if not properly installed or removed. They are not recommended for creeklines or waterways.

Installing plastic tree guards

• Gather your materials. You will need a tree guard, three sturdy stakes, a hammering tool and weed mat (optional). The hammering tool pictured is like a small post driver, a tube of good gauge steel capped with a steel plate. This tool is great with bamboo stakes as it does not slip off the stake and minimises bending when hammering. 

• Firmly hammer two stakes in a line behind the planted seedling. Positioning the stakes so the seedling will be in the middle of the triangle formed by the tree guard. Ensure the stakes are perpendicular or have a slight lean away from the seedling. Any lean toward the seedling will result in the guard becoming loose and easily blown away. 

• Place the guard over the two stakes and the seedling then, using the third stake, pull the guard taught to create the triangle. Firmly hammer the stake, again ensuring it is perpendicular or has a slight lean away from the seedling. The guard should feel firm when pushed. The installed guard should remain serviceable and resilient to most wind storms and small animals for a year or so, after which it should be removed for reuse.   

Cardboard carton guards

Wax coated cardboard cartons with two supporting stakes have less environmental impact as the cartons and stakes are biodegradable.

Installing cardboard tree guards

• Gather your materials. You need a carton, two stakes, a hammering tool and a weed mat (optional).   

• Firmly hammer one stake next to seedling at a distance approximately half the width of the carton.

• Opening the carton you will notice that two of corners are on the flattened side of the carton and two on the edge. Place the carton over the stake and seedling ensuring the stake is positioned in one of the corners that was originally flattened (otherwise the guard will return to its manufactured shape, which is flat).
• Using the second stake pull the opposite corner out to finish the square, hammer in firmly ensuring the stake is perpendicular or has a slight lean away from the seedling. The flat pack manufacture of the carton ensures that the natural spring of the carton keeps it taught and square.   

Calendar guide for revegetating with seedlings

Autumn the year before you plant:

• Order seedlings as soon as possible, ideally before the end of December.
• Rip before the autumn break while the ground is hard and dry to get deep shattering of the soil.
• Control exotic perennial plants if they are actively growing.
• Pest animal control. Ensure chosen pest control methods do not irreparably damage existing native plants, native animal habitat or culturally important sites.

Summer:

• Complete all fencing and infrastructure  

Mid-autumn to early winter:

• Final site preparation including slashing, weed control and finer cultivation.

Late-winter to early spring:

• Planting, provided there is a good soil moisture profile 

Your next steps

Get advice on:

• plant species selection
• direct seeding for native revegetation
• planning your on-ground revegetation works.