TEACHER TIPS 4: A focus on plant maintenance

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Plant maintenance, just like growing unit maintenance, is necessary for the  long term survival of planted trees which is a very important part of any successful restoration programme. A high survival rate is virtually assured if the seedlings are robust and healthy when planted out.

Key factors in producing robust and healthy trees for planting out are:

  1. Favourable growing conditions
  2. Successful ‘pricking out’ and ‘potting on’
  3. Absence of pests
  4. Effective hardening off

Managing optimum growing conditions essential for producing healthy seedlings

A well maintained TfS Plant Growing Unit

In TEACHER TIPS 3 growing unit maintenance was highlighted because a well-maintained growing unit will provide optimum light, water and shelter needed for healthy growth.


Growing units using shade cloth provide the optimum light for growing healthy native seedlings. The location of the growing unit is important to ensure that it is not in a shaded spot for extended periods during the day. As seedlings get larger make sure they are not overcrowded since all plants should access the same amount of light.

A poor watering regime can lead to this sort of disaster

The soil in which the seedlings are grown should be kept moist at all times. This is best done with an automatic watering system which distributes water evenly. Make sure that the plants don’t get waterlogged by over-watering or dry out because of insufficient watering. The best way to do this is to set your automatic timer to go on in the morning and late afternoon, then over a period of a few days check the soil moisture regularly. You can change the length of watering time if the soil appears too dry or too wet but it is best to keep watering twice a day.  Remember plants will require more watering in summer when the sun is out than they will in winter.

Read about the proper installation and maintenance of your water timer.

Most well-designed growing units will provide sufficient shelter from wind, driving rain and frosts. The TfS Plant Growing Unit (see picture above) has the additional advantage that the side curtains can be drawn back to allow in more sunlight or closed to reduce light and add protection from the wind etc.

However, probably the most important factor ensuring healthy growth is regular monitoring of the conditions in the unit and responding accordingly if changes are needed.

Root trainers in their baskets ready for pricking out seedlings

Proper pricking out and potting on techniques ensure maximum growth
Schools may grow seedlings from seed or receive punnets of tiny seedlings.  When these tiny seedlings are about 3cm high they need to be pricked out into their own growing container – in most cases a root trainer, although some prefer small individual pots. The main purpose of the root trainer is to ensure that the new roots will grow downwards more than outwards thereby ensuring the development of a good root mass when they are potted on later.

When pricking out is completed the seedlings should be standing up straight, have no roots visible at the soil surface, have no leaves buried in the soil and the stem should be completely visible above the soil. Read more and see a short video on pricking out.

Small seedlings need to be carefully pricked out to ensure healthy growth

After about four months seedlings can be transferred from their root trainers to larger pots or bags. TfS encourages schools to either use 1 litre milk cartons (which are biodegradable) or PB 3/4 black polythene bags (which can be reused).

Just as for pricking out, when potting on has been completed the seedlings should be standing up straight, have no roots visible at the soil surface, have no leaves buried in the soil and the stem should be completely visible above the soil. Read more and see a short video on potting on.

Recently 'potted on' seedlings in the PGU

Seedlings can be 'potted on' into plastic bags or milk carton








In general if potting mix with added nutrients is used as the growing medium no extra fertilizer needs to be added to the soil. However, after ‘potting on’ when the seedlings put on a growth spurt, because their roots have more space in which to grow, a foliar spray can support healthy growth above the ground.

Pests will prevent growing healthy and robust trees.
When plants grow without competition from pests such as weeds, insects, fungi, slugs and snails, they grow faster and bigger and therefore become more resistant to pest attack. 

An aphid infection on the underside of a leaf

First, it is important that weeds are regularly removed from pots and root trainers. Weeds not only compete for resources with your growing plants but they can also result in miss-shaped and distorted plant growth form.

Secondly, teachers need to be aware that while many commercial products are available to kill off pests such as insects, fungi, slugs and snails it is important to consider more environmentally sustainable pest control.


Powdery Mildew can have a serious effect on plant growth

For example, rather than using a commercial insecticide why not try using a soap spray made by mixing 1-2 tablespoons of liquid soap (not detergent) with a litre of water and spray onto your plants, making sure there is a fine coverage both on top of and under the leaves. You may even wish to try a baking soda spray to treat for an attack by the mildew fungus. Just mix a tablespoon of baking soda with half a tablespoon of cooking oil in about 2 litres of water and spray as above. Testing the effectiveness of various sprays would be an excellent classroom experiment.

Harden off your plants before planting day
Before planting out trees which have been grown in the shelter of a growing unit maybe for more than a year it is essential that plants be hardened off. According to DOC all native plants need to spend four to eight weeks in the open to harden off prior to planting out. Only those species that are to be planted under a canopy or sheltered area should be left in the shade house. Plants left out in the open to harden off need good shelter from wind with a hedge, building or other type of wind-break.

Seedlings prior to planting being 'hardened off'


Young trees ready for planting out








A final tip
A growing unit containing labelled plants is beneficial not only for ongoing management (plant counts, growth assessment etc) but also assists students with their plant identification.

Labelling plants in the growing unit is a great strategy for teaching plant names

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