Propagating conditions

What conditions do leafy cuttings need?

1. Very high air humidity;
2. Moderately low light intensity;
3. Equable temperatures;
4. A suitable rooting medium;
5. Protection from wind, heavy raindrops, pests and diseases.

Arrows show water movement; double lines show barriers to it.

Which is the most important?

Lack of any one requirement can damage or kill cuttings. However, keeping them always at a very high humidity (A 34) is the most important, because:

1. most unprotected leafy cuttings lose a lot of water within minutes, even in the humid tropics, by evaporation from their leaves (and stems);
2. at first they have no root systems, so water uptake is slow;
3. even when roots have begun to form, they might not absorb enough water to replace what would be lost by evaporation in the open.

How do I keep cuttings from drying up?

1. By shading the propagation area (A 33);
2. By trimming the leaves (A 41) before taking the cuttings (A 42); and then putting them straight into a polythene bag;
3. By taking them when it is cool and humid (A 34);
4. By rooting them in a poly-propagator, or under automatic mist or ‘fogging’;
5. By keeping them moist with a hand-sprayer while preparing (A 43) and setting them (A 44), and whenever the propagator lid is open;
6. By potting up and weaning rooted cuttings carefully (A 53–54);
7. By checking the conditions regularly (A 50).

Why can't I just stand the cuttings in water?

A few tree species can be rooted this way, but:

1. gums, latex or mucilage, or air bubbles, can block entry of water;
2. the water may quickly go foul, unless aerated as in a ‘bubble-bath’ system (A 40);
3. such root systems can be difficult to transfer successfully to soil.

What is a poly-propagator like?

It is built with a simple frame covered with clear (or white) polythene sheeting, and contains a reserve of water below a moist rooting medium (A 31).

What about automatic mist?

Here the cuttings, set in a well-drained rooting medium, are repeatedly moistened by fine mist produced by water at high pressure passing through special mist jets (A 32).

What is ‘fogging’?

A greenhouse system in which a powerful fan forces many very fine droplets of water into the air. Most of these evaporate, keeping the humidity high even when the vents are open.

Which is the best method?

Poly-propagators are best, at least to start with, because they:

1. re cheaper, and easy to build from locally available materials;
2. do not rely on piped water under pressure;
3. are simpler to operate, with less risk of breakdown;
4. can give better results than mist with some species;
5. can be used either for small or large scale propagation.

When are automatic mist or ‘fogging’ needed, then?

1. for species that root better when covered with fine drops of spray;
2. for research on rooting cuttings at a well-equipped centre;
3. when found to be appropriate for bulk production of rooted cuttings.

What sort of rooting medium is suitable?

One which allows good aeration, retains moisture (but does not get waterlogged) and encourages good root development.
Mixtures of several locally available materials can be made into good rooting media (see A 35 for more details).

Why should I shade the cuttings?

Because:

too bright sunlight may cause overheating of the cutting, or of the air in the polypropagator, both of which can dry out or damage the leaves.

But:

too dim light does not allow the cutting to manufacture much sugar by photosynthesis, which is important for rooting; and it encourages the development of disease.

What is the best way to shade the cuttings?

This is described in A 33.

I can't control the temperature, can I?

Adequate shading should usually stop the air temperature in a poly-propagator from rising above 28–33°C, and the temperature of the rooting medium above 25–30°C.
At higher altitudes and latitudes, try to choose a warmer site, as air temperatures below 16°C, and bed temperatures below 21°C may depress rooting. (If electricity is available, flexible cables and thermostats are available (A 63) to warm the rooting medium to an optimal level - often 25–30°C, while leaving the air cooler.)

Do I need to measure the conditions?

A thermometer with a range from 10–50°C is useful, and there are dials which give a rough idea of relative humidity. When the sky is overcast, a camera at a fixed distance can be used to compare light reflected from a large sheet of white paper. For instance, if the light meter calls for an exposure that is twice as long, then the light level is about 50% of the previous reading.
(Note: Sensors that measure temperature, relative humidity and light accurately may be needed for research.)

What about protection from wind?

1. Put up screens made of polythene sheeting, shadecloth, mats, etc, to protect the propagation area, especially the place where cuttings are prepared (A 43);
2. grow hedges and/or lines of trees to check wind movement, especially to prevent disturbance to automatic mist systems;
3. secure poly-propagator lids, temporary covers, shading and screens against storms.

What about heavy raindrops?

These can knock over or damage cuttings in mist propagation beds. The overhead shading will reduce the impact of the rain; if necessary build a sloping ‘roof’ of polythene sheeting to direct water off the beds.
Lids of poly-propagators may be damaged by pools of standing water.

How should I protect against pests and diseases?

This is described in sheet A 52.

What about leafless cuttings?

The rate of drying up is much slower with these, especially if the stems are no longer green, but are protected by a layer of bark.
They don't need a special propagation conditions, and can be rooted in the open ground (A 4).

How big should poly-propagators be?

They can be built to suit the conditions, materials and space available.
A convenient size is often about 1 m wide × 2–4 m long. The height should be between 0.5 and 1 m, with a sloping cover.

What materials are needed to build one?

1. Frame: wood (metal or concrete are alternatives);
2. Covering: a thick grade of clear (or white) polythene sheet;
3. Filling/drainage (below rooting medium): stones, gravel, sand;
4. Fixing materials: nails, office stapler and drawing pins to join and fix polythene sheeting, hinges + screws, clips to secure cover against storms.

How much of them is needed?

To build one wooden poly-propagator 1 m wide, 3 m long and 0.5–1 m high:

1. Wood: 250 × 25 mm - 8 metres length;
                 50 × 50 mm – 10 metres length;
                 50 × 25 mm – 32 metres length;
2. Polythene sheeting: 2 m wide – 10 metres length.
3. Stones or broken cement blocks (30–120 mm) - 0.5 m³;
   Gravel (5–10 mm) - 0.25 m³
   Coarse sand - 0.25 m³.

All the filling/drainage material needs to be thoroughly washed before use.

Won't the wood rot?

Durable, termite-resistant wood should be used, especially for the parts in or resting on the ground. Alternatively, the wood should be treated with a preservative that will not damage the cuttings.
You could attach the polythene sheeting on the inside of the framework, so that the wood is not permanently wet.

What should I do when the timber frame has been made?

Attach the polythene sheeting, making doubly overlapping joins between one sheet and the next. Use a single piece without holes for the whole of the base plus the lower 0.3–0.4 m of the sides. This should be left loose enough so that when it rests on the ground it will hold the filling/drainage without excessive strain.

Is the poly-propagator now ready to fill?

Not yet. First align its long axis east-west, and then dig four small holes to anchor the ‘legs’ at the corners of the propagator;
Level out the ground between these holes, and spread sand to protect the polythene sheet from getting pierced or stretched;
Make sure the propagator stands level, and then fix it in place with stones;
Put a short piece of plastic pipe or bamboo vertically in the corner (25–30 cm long and about 5 cm in diameter). This will let you check the correct water level easily, and add water if needed, without soaking the rooting medium.

What do I put in first?

Add carefully, so as not to damage the polythene sheet:

1. a thin layer of sand;
2. a thick layer of stones;
3. a thick layer of gravel;
4. a thin layer of sand (adding up to a total of about 15–20 cm).
   Then add water until the filling/drainage layer is fully saturated.
   (Mark where this level is in the plastic tube.)

What about the rooting medium?

Now add about 10 cm depth of rooting medium on top (see A 35). It should be moist but not waterlogged, or the cuttings will not thrive.

What about the cover?

This should be set at a fairly steep angle:

1. to encourage water droplets that condense on the underside of the polythene sheet to run off, instead of forming large drips;
2. to make it easier to work on the low side of the poly-propagator.

The cover can either be attached with several hinges, or can be made in two sections, sliding to and fro. (In both cases it must close tightly!) Make a simple catch to prevent the lid blowing off in a storm.

Is a misting system needed?

This is a non-mist propagator - no need for automatic misting (A 32); However, a clean hand or knapsack sprayer giving a fine spray of water droplets is required, for use:

1. while cuttings are being set (A 44), or potted up (A 53);
2. whenever the propagator is opened (A 34);
3. if the rooting medium needs to be moistened (A 35).

What about shading?

This is essential, and is explained in sheet A 33.

Does the poly-propagator need any maintenance?

Not a lot:

1. clean the outside of the polythene sheeting each week with water and a soft cloth, to avoid scratching it.
   Clean the inside in the same way, preferably just before putting in a new batch of cuttings;
2. check the water level each week, and add more if needed, down the plastic pipe;
   (NOTE: do not saturate the rooting medium!)
3. patch any holes in the polythene sheet with a small piece of sticky tape, or polythene sheet glued on.

What is mist propagation?

The rooting of cuttings carried out under frequent bursts of a fine water spray.

Is this to stop them drying up?

This is the main reason. Little water is lost by the cuttings because:

1. the relative humidity of the air near the shoots is kept very high by the evaporation of the mist;
2. the leaves and stems are covered by many small drops of water, which further reduces evaporation from the cutting.

The mist also tends to lower the temperature of the shoot, through:

3. the evaporation of mist which cools the air;
4. the small drops of water acting as a screen to the sun's rays;
5. the water temperature often being lower than the propagator.

What sort of shading is best?

Plastic shadecloth (50–70% shade) at 2–2.5 m above the whole area (A 33).

How is the mist produced?

By passing water under pressure through mist jets, which are very small, specially made holes. A complete system consists of:

1. A water supply (river, well, reservoir, large tank or piped mains);
2. An electric or diesel pump capable of supplying enough water at a pressure of at least 15 m head, plus a pressure switch and controls;
3. A filtration system which removes particles that would block the mist jets, and can be routinely cleaned;
4. A mist controller (mains- or battery-operated) with a timer that allows adjustment of:
   1. the length of each burst of mist (2–15 secs);
   2. the frequency of the bursts (every 2–60 mins);
   3. a different regime for day and night;
   Alternatively, some controllers have an electronic sensor which detects the evaporation of the mist (or whether the sun is shining), and controls the frequency and length of bursts.
5. A set of mist jets, preferably with valves to turn off those that are not needed.

How often should the controller give bursts of mist?

This depends on the climate, the season and the species. A rough guide to start with is:

06.30–18.30 - 10-second bursts every 4 minutes;
18.30–06.30 - 5-second bursts every 45 minutes.

Won't so much water make the cuttings rot?

Too much water can be a problem. It is best to try out different regimes using a common plant species that roots easily, even a weed.
Work out by trial and error how much mist is needed to keep some water droplets on the leaves during the middle of a hot, sunny day; and throughout a night when there is some wind but no rain.

What about when there is heavy rain?

This can also cause problems. These are some of the things you can do:

1. Make sure that there is very good overall drainage of the site, that can deal with:
   1. heavy rain during thunderstorms;
   2. less heavy but prolonged rainfall;
   3. the water from the mist. (This can be surprisingly large - to calculate the equivalent daily ‘rainfall’ caused by the mist, put some cylindrical containers containing a little oil on the bed, and find the average depth in millimetres of water collecting in them during one day. The oil will collect above the water and stop it evaporating.).
   Unless the subsoil is extremely permeable, good drainage needs to be achieved by combining sufficient slope, adequate ditches and enough stones & gravel below the rooting medium.
2. Arrange any overhead plastic shadecloth (A 33) so that the lowest point is over a ditch (or path), not over a propagation bed.
3. If necessary, lay polythene sheeting under some parts of the overhead shading, as a ‘roof’ to protect the propagation bed.

How wide should drainage ditches and paths be?

Paths need to be wide enough to allow a wheelbarrow or small trolley to pass; ditches should be adequate to catch and carry away water.
On the other hand, keeping the propagation beds close together means that the relative humidity will tend to be higher.
One possibility is to combine the drainage ditch with the path, by filling the ditch with large stones, then coarse gravel, and a finer gravel on top to make a good, clean path.

How should the propagation beds be constructed?

1. so that the top of the rooting medium is at least 30 cm above the level of the paths;
2. construct the sides of the bed out of durable wood or concrete blocks, leaving plenty of space for water to drain out at the bottom;
3. fill the bed with the same materials as for polythene propagators (A 31), but:
   • without polythene sheeting;
   • with a thicker layer of both stones and of gravel;
   • without flooding the filler/drainage material with water;
   • with a rooting medium that does not easily become waterlogged (A 35).

How wide should the beds be?

Between 1 and 1.25 m, so that one can reach the cuttings in the middle.

Won't the wind disturb the mist?

Yes, this can be a real problem. One answer is to put a vertical screen of polythene sheeting all around the propagation bed, up to 30–40 cm higher than the mist jets. (NOTE: do not close off the top!)
Or you could use an extra line of mist jets upwind of your propagation.
Other suggestions for tackling wind problems are given in A 30.

Won't shading make the trees too soft to survive planting out?

No. As with germinating seeds (Manual 2), shading is used to protect the young plants at a critical stage. Later on, when their root systems have developed, shading is progressively reduced so that the plant becomes ‘hardened’ to full sun (A 54).

Should the shade cut out direct sunlight completely?

No. It should allow about 15–25% of full light to reach the propagation bed in a poly-propagator, or about 30–50% for mist propagation.

What kind of shade is best for cuttings?

Use local materials such as matting, woven bamboo, palm-leaf or similar leaves. Or you could buy plastic shadecloth (A 63), or metal sheets with some translucent panels. The shading should:

1. be as even as possible, avoiding both large sun-flecks and areas of dark shade (having the long axis of the poly-propagators east-west is best);
2. extend at least 2 m further than the propagation beds in each direction, so that unshaded sunlight does not reach the cuttings in the early morning or late afternoon. Alternatively, supplement the overhead shade with mats or pieces of shadecloth hanging vertically, or with palm fronds fixed into the ground.

What is the best way to support the shade?

Build a wooden framework at 2–2.5 m, well above head height, over the whole propagation area, including the work area where cuttings are prepared (A 43) and weaned (A 54).
Choose a spacing that fits the sizes of the shading material, and put the uprights at the edges of the propagation beds (polythene sheeting could protect them from being soaked by mist.)

Is plastic shadecloth easy to use?

Yes, and it can last for several years if put up and fixed well (see A 24).

How is it fastened?

By tying it at intervals to the framework. It can be easiest to join some of the pieces together before putting them up.

What about leaves and branches falling on the shading?

Leaves can increase the amount of shade cast, and it may be necessary to arrange access to be able to remove them. Damage from twigs and small branches can usually be repaired easily.

When do I need to reduce shading?

1. For mist propagation during the rainy season - less shading may be needed, because it is usually cloudier. Have two layers of shadecloth, and remove one; or take off some of the palm leaves; (Watch out for bright sunny spells!)
2. For weaning rooted cuttings that have been potted up - Make several small, temporary shading frames, and interchange them to increase the amount of light gradually (A 54).

Why is high humidity so important?

Because below about 90% relative humidity cuttings will soon dry up (A 30).

When is it most likely to drop?

1. in the middle part of the day, especially if the air temperature inside the polypropagator goes above 30 °C;
2. immediately the poly-propagator is opened.

%RH=relative humidity (per cent). Immediately the poly-propagator is opened, the air becomes much drier, even when a hand-sprayer is used ----.

How should I keep humidity up?

(1) in poly-propagators (A 31) by:

1. using enough shading, though not too much (A 33);
2. keeping the propagator shut as much as possible;
3. spraying the cuttings with fine droplets of water weekly, and whenever the propagator is opened (if necessary each night and morning).

4. taking (A 42), setting (A 44), checking (A 51) and potting up cuttings (A 53) early or late in the day, or during misty weather;
5. checking the water level each week;
6. mending any tears in the polythene sheeting.

(2) with mist propagation (A 32) by:

1. preventing wind from disturbing the mist (A 30);
2. operating extra lines of mist jets on each side of the beds containing cuttings.

Won't all this moisture make the cuttings rot?

Yes, there is an added risk of fungal attack. However most rotting is not of healthy cuttings, but of those that have been damaged, leaves that have been shed, etc. There are several things that you can do to discourage disease, like not having too much shading (A 33), using a well-aerated rooting medium (A 35), changing it regularly and removing shed leaves and dead cuttings promptly (A 52).

Does the soil need to be very humid too?

No, not at all. In fact it is better if the rooting medium in a poly-propagator is not watered unless it is starting to dry off. The level at which roots are forming should stay moist from:

1. the moisture added when it was originally prepared;
2. the water lying beneath it;
3. fine spraying of water on the leaves of the cuttings;
4. drips from condensation on the polythene.

In mist propagation, a very freely-drained rooting medium is needed, which does not become waterlogged from the mist plus rainfall.

Can humid air restore wilted cuttings?

They may recover slowly, but it is better to submerge the shoots in water for an hour or two. Afterwards, very humid air can prevent them from losing so much water by evaporation that they wilt again.

Why do I need a special rooting medium?

Because most cuttings root much better in one than in ordinary soil.

What are the features of a good rooting medium?

1. Aeration: for successful rooting, the base of the cutting has to receive an adequate oxygen supply from air spaces in the medium;
2. Moisture retention/drainage: the rooting medium needs to hold moisture, but not be easily waterlogged;
3. Mechanical properties: holes for cuttings should not collapse, cuttings need to be supported, and the roots must be free to penetrate the medium;
4. Clean: Sand, grit and gravel should be washed before use, and other components should not be full of troublesome weeds, animal pests or disease-causing moulds.

CO₂=carbon dioxide; O₂=oxygen; H₂O=water.

Are rooting media difficult to make up?

Not at all. Many of them are mixtures of common materials, such as sharp sand, grit or fine gravel, old weathered sawdust and coconut palm husks. It is not necessary to buy materials such as peat, vermiculite or perlite, except for special purposes.

Why do I need to mix different components?

Because most of them have weaknesses as well as strengths. For example:
- grit and fine gravel are good for aeration and drainage, and can be clean, but are poor for moisture retention and mechanical properties;
- old weathered sawdust is good for moisture retention and mechanical properties, but has to be watched for cleanliness.
Note:- most tropical sawdust has to be ‘weathered’ by leaving it in the open for about a year to break down toxic chemicals.

Can the same media be used for mist propagation?

Free drainage is very important under mist, especially if the beds receive rainfall as well as the considerable amount of water from the intermittent mist. There should be plenty of grit or fine gravel in the mix, therefore.

What mixtures are recommended?

Try 33% grit or fine gravel : 33% sharp sand : 33% old sawdust for poly-propagators (moisten the medium while mixing, but do not soak it);
Try out 50% grit or fine gravel : 50% old sawdust for mist propagation.
The fibre within partly rotted oil-palm stems can be mixed with sharp sand, and old, outer husks from coconuts are greatly prized as a rooting medium.

Will adding fertilisers help the cuttings to root?

No, this might actually hinder rooting, and can encourage small green plants like mosses and algae to grow on the surface of the medium.
Although the leaves of cuttings may go a yellowish green because of a shortage of nutrients, the time to replace these is when potting up (A 53) and when feeding nursery plants (Manual 3).

How often should I change the rooting medium?

As soon as there are signs of unexpected rotting, pests or poor rooting.

When should I consider rooting in containers?

Problem 1) If the numbers of rooted cuttings you produce is getting larger;
Problem 2) If you find a species with unexpectedly high losses during weaning;
Problem 3) If the root systems in conventional black polythene pots are causing trouble after planting;
Problem 4) If you want to do research on plant handling, growing or planting;
Problem 5) If you would like to transport plants over long distances.

Why is this so?

Problem 1) Because handling and potting up the cuttings could be easier and more successful (A 53);
Problem 2) Because root damage can be minimised with containers;
Problem 3) Because rooting in ‘root-trainers’ could be the answer;
Problem 4) Because you could reduce the variability of your test plants (A 45);
Problem 5) Because this might offer a ‘middle way’ between the costs of sending heavy, bulky plants in conventional black polythene pots and the risks of drying out with bare-rooted stock (see Manual 5).

What kinds of containers are suitable?

Any type can be used, including those made of polythene or bamboo but large ones take up too much space in the propagating bed. The best kinds allow free drainage and promote good root systems, such as root-trainers and biodegradable types. However, these have yet to receive extensive tropical tests, so use them first on a trial basis, filling them with a good rooting medium (A 35).

What is the difference between them?

1. Root-trainers have grooves which make the roots go vertically downwards, and are meant to be kept clear of the bed so that roots do not emerge from the bottom. Each contains 4 – 6 sections, and the whole set can be opened to remove the plants without much damage to their root systems. Around 6 – 10 sets go into a carrying tray for easy handling.
2. Biodegradable pots and tubes are made of material which rots after a period of up to 3 months. Their great advantage is that the rooted cutting is potted up or planted out as it is, without taking it out of the pot. Tubes especially need to be supported in trays that will stop the rooting medium falling out of the large hole at the base.

What size of container is best?

Narrow, deep containers are preferable, but larger cuttings may need somewhat wider pots. Top diameters of 2 – 6 cm, and lengths of 10 – 20 cm are suitable, as they don't take up too much space, and the rooted cuttings can easily be potted on into standard polythene pots (A 53), or planted directly into the ground.

What is the most important reason for using containers?

To stimulate the formation of correctly shaped and vigorous root systems which need not be disturbed much, so that trees will establish rapidly after planting out.