Greenhouse Propagation

Propagation by Seed

This is an invaluable source of new plants for the greenhouse and a relatively cheap way of increasing the collection. Because there are few nurseries specialising in unusual greenhouse plants they are often only available as seed. Most seed ordered from reputable firms comes with precise instructions as to how it should be sown. This information is the result of much research on the part of the seed company. In order to get the best results and value from your seeds always follow the instructions as closely as you can.

Moisture is a general requirement for germination and usually has to penetrate the seed coat to start things off. Sometimes germination inhibitors need to be washed away from the seed coat to break dormancy. With large or very hard seed it is sometimes necessary either to soak in lukewarm water or graze the seed coat with a file to speed the process up. Small hard seed can be rubbed firmly between two layers of sand paper. Some people like to nick the seed coat with a knife but I feel there is more likelihood of damaging the embryo plant inside; Any damage to the seed coat should be done away from the tip or ends of the seed.

Light is usually required for germination and some seeds will not germinate without plenty of it. Small seed especially is often surface sown not only because they are too tiny to be buried but because they need all the light they can get. There are also seeds which prefer to germinate in the dark and need to be not only covered with compost but placed in a dark place or covered in some way.

Temperature is important as most seeds have an optimum temperature range at which they will germinate best. This is where it pays to have a thermostatically controlled propagator as part of your equipment. It is not just a question of keeping them as warm as possible. Some seed will not germinate if the temperature rises beyond a certain point.

With all these variables it is obvious that the more information you have concerning the preferences of the seed the best results you will get.

Compost Proprietary peat-based composts are easily available and reliable. The major problem is that they are not as free draining as I would like, in other words they lack sharp sand. The addition of this renders them suitable for a much wider range of seeds.

Loam-based composts, largely represented by John Innes seed compost, are, although the original formula is good, rather variable and can be too stodgy for my liking. There is an excellent compost available from Silvaperl containing fine vermiculite from which I have had good results both for sowing and pricking out.

Method It is essential to prepare pots and pans adequately before sowing. Overfill the container with compost, scraping the compost level with the top using a thin wooden board. Make a collection of ‘pressers’ of various shapes and sizes so that the surface of the compost can be pressed firmly but gently down. When you are satisfied that the surface is even and free of lumps place it on a level surface and water thoroughly using a can with a fine rose. Never begin or finish watering when the can is over the container as heavy drips from the rose will make craters on the surface. If the compost is very cold allow it to warm up before sowing seeds that will need a high temperature. When sowing fine seed this elaborate preparation will pay dividends as seed will not fall down fissures in the compost.

Sow thinly and evenly on to the surface of the compost. It is often recommended that silver sand is mixed with fine seed so that if you cannot see the sand at least you can see something coming out of the packet. Personally I find great trouble with this as the seed is invariably of a different density to the sand and they always seem to separate out so that you might sow all the sand first and a great burst of seed at the end in a heap. I find it easiest to sow from the packet by very slowly and carefully tapping the packet with one finger whilst moving it over the surface, first going around the edge of the container and finishing with the middle. If seed is not to be covered with compost I press it in gently with a dry presser. Providing the compost is moist it is not necessary to water it in. Should subsequent waterings be necessary either do this with a fine mist spray or by standing the container in water. Some seed, though fine, benefits by having a delicate sieving of compost over it which is then pressed down so that it is nestling in rather than covered by compost. Larger seed can be scattered or space sown over the surface and is usually covered by its own depth of compost. Watering in can then be done using a fine rose. Sometimes, especially early in the year, algae grow on the surface of the compost before the seeds germinate. This smothers the seed and makes it far too wet. A very fine covering of vermiculite which has the useful property of letting light through is a good precaution to take if this is likely to happen.

I usually cover fine seed with plastic film before placing them in the propagator. If you are fortunate enough to have a mist unit with a heated bed even fine seed need not be covered but only quick germinating seed will take kindly to being so continuously moist. Providing seed does not mind germinating in the dark the airing cupboard is a very useful alternative to a propagator.

Be sure to remove seed to a light place as soon as germination takes place. Seed germinated in a propagator should either come out when germinated or if the temperature outside the case is too low at least get some ventilation on. The reason for this is that should there be any danger of damping off close warm conditions will make the situation worse. If damping off ever occurs take the precaution of watering all seed and seedlings with the appropriate fungicide. This practice should then become routine as when the disease has arrived it is likely to strike again.

Pricking Out

Just as the first true pair of leaves begins to show beyond the cotyledons (seed leaves) is the ideal time to prick out most seedlings. Preparation of the compost in the container should be done with the same care as for sowing. Always hold the seedling by a leaf and never by the stem which could bruise it and lead to fungal attack. Seedlings of monocotyledonous plants (bulbs, Asparagus, grasses) can be left a little longer until two or three leaves have appeared.

Sowing Fern Spores

Spores can be bought from seed companies or collected off your own plants. You will notice that under the fronds are rusty looking patches which are the sort which hold the spores. Keep a close eye on these and eventually they will change slightly in appearance and begin to shed spores. As soon as you notice this beginning to happen cut the frond from the fern and either place it in an envelope or between two sheets of paper, keep this in a dry place and within a few days the spores should all have been shed and will look like a collection of dust with a few larger bits and pieces. It is the dust which you need to collect and not the larger bits which are only pieces of spore case. If you cannot bear to remove a frond from your fern move it to a dry place away from other ferns and stand the plant on clean white paper. When the paper is covered with spores remove them to sow. It pays not to delay the sowing as fresh spores will give better results.

The best compost to use is a mixture of three parts moss peat to one of sharp sand. Fill a shallow pot with the mixture, sieving the top 2.5 cm (1 in) to give a fine surface which should be pressed down to give an even finish. It is far better if you can sterilise the whole thing which is simply done by drenching the pot and compost with boiling water applied through a watering can with a fine rose. Leave this to cool and allow excess water to drain away before sowing. The reason for this is to get rid of fungus and moss spores which might interfere with the fern spore germination. Having said this I have, when short of time, sowed spores of mixed greenhouse ferns and spores of Dicksonia without sterilising and have achieved good results.

It is very difficult to spread such fine spores evenly over the compost but having done so do not press them in or cover them with more compost. This is why it is important for the surface to be pre-moistened. Stand the pot in a saucer with water in it and place a polythene bag over the top. Always water from the bottom. Now a position of warmth (25°C, 77°F), humidity and shade is required. In summer just under the greenhouse staging is ideal, but in winter a propagator will be necessary. Germination can take anything between a few weeks to a year or more. The first thing to happen is that a green film looking a bit like liverworts will spread over the surface. Do not throw this away because it is the prothalli or initial growth of the fern which contains both male and female organs.

Providing moisture is present fertilisation will take place enabling the spore-bearing part of the fern to develop. This is the frond part which is more easily recognisable as being a fern.

Once small fronds start to appear (or before then if things are getting a little crowded), small patches of growth can be transferred to new, sterilised if possible, compost. Tweezers are best for this job and the patches are just nestled on to the surface. When young ferns are clearly discernible they can be separated into individual pots and grown on.

Vegetative Propagation

Unless you have a good range of sophisticated equipment, including lighting and thermostatically controlled propagators, I would not recommend trying any of these methods during winter when natural light and temperatures are low. Much better returns for your time and effort will be gained by carrying out most propagation during spring and summer.

Division

Probably the simplest form of propagation is division. This is used to multiply plants which form clumps or several different crowns of growth in one pot.

Plants, making sure that both sections have healthy leaves and roots.

Usually this is done when the old plant becomes pot bound and the roots are straining at the side of the pot. Knock the old plant out by turning the pot upside down and tapping the rim sharply against a hard surface. If this is no good try whacking the rim of the pot away from the plant with a trowel handle or stout stick. Failing all else, break the pot but never pull the plant to get it out of the pot as you may be left with a handful of leaves. If the root ball is not too solid carefully prise the clump into several manageable pieces which can then be repotted.

If this is impossible try putting the plant on the floor and using two forks back to back as if it were a herbaceous plant. I tried this with a vast Aspidistra once and it worked a treat.

Having potted the new plants up water them in but be sure to allow the compost to become just dry to the touch on the surface before watering again. This is a crucial stage when ovcrwatering can kill, especially with Spathiphyllum, Maranta and Calathea. Do not feed until a few weeks have passed and you think the roots might have grown into the new compost.

Offsets

Sometimes, when dividing a plant, it is impossible to pull sections apart as they seem to be joined by an underground stem. This is seen in Sansevieria and bromeliads. This is because the new plants are produced as offsets from the parent. All that is needed is to cut through the stem joining the plants together with secateurs or a sharp knife. Offsets are not always underground and may be produced around the top of the plant. Cacti, Cryptanthus and some bulbs are examples. When the offsets are a good size they can be cut or pulled off and treated as a cutting until they have grown their own roots.

Cuttings

Parts of the plant which are cut off and encouraged to grow their own roots and subsequently become new plants are cuttings and there are many different types. While rooting, it is essential for most that they do not become waterlogged. A good rooting compost is equal amounts of moist moss peat and sharp sand or grit. The sharp sand can be replaced by perlite or vermiculite or can be a balance of all three. No fertiliser is necessary. It is also important in most cases to give cuttings humidity in which to root. This is to prevent them from losing too much moisture at a stage when they have no roots to compensate for it. This can be provided by a propagating case, covering of plastic or by using a mist unit. They should also be shaded from hot sun. Things are never as straightforward as they sound and as well as providing humidity, conditions should not be so close that cuttings are in danger of rotting so some provision for ventilation must also usually be made. Cuttings which dislike humidity while rooting include cacti, succulents and Pelargoniums.

Softwood Cuttings

The majority of greenhouse plants can be propagated by softwood cuttings. These usually consist of a shoot tip and 8-10 cm (3-4 in) of stem which is all growth that has been made in the current season. It is best to take the cuttings straight from the plant but if there has to be a delay in making and inserting them they should be kept in a plastic bag away from direct light. One common mistake is to make cuttings too long. A long straggly cutting will make a long straggly plant and only very large growing plants with long internodes should make long cuttings. Nodes are swellings on the stem from which leaves and shoots arise. It is from here that roots usually develop. Internodes are the lengths of stem where nothing is going on. To make a cutting cut under a node and take off any bottom leaves that would end up under the soil. If the plant has long leaves these can be cut in half which keeps the leaf area down and thus saves moisture loss. This also makes it easier to insert five average-sized cuttings to a 9-cm (3-½-in) pot. This may sound like overcrowding but in fact is the best thing to do; not only is one cutting per pot a waste of space but they will not root so well either.

With plants such as Philodendron and Scindapsus one is often presented with one long shoot armed with many nodes to make cuttings from. Not only can the tip be rooted but stem sections usually of two to three nodes. Cut above a node at the top and below at the bottom.

Hormone rooting compounds are generally a good thing as they speed up and improve rooting although there are a few plants such as Ficus which tend to do better without them. The powders have a limited shelf life so if you have been using the same pot for the last ten years stored in full sun on the greenhouse shelf throw it away and buy some more. I find the liquid products very good as they can be made up fresh each time they are required.

Semi Hardwood Cuttings Sometimes there is the opportunity to take a side shoot of just the right length as a cutting. It can be pulled off the parent plant in such a way that it comes away with a small ‘heel’ of older wood from the main stem. These and cuttings of wood from the previous year can be called semi ripe. These will apply mostly to shrubby greenhouse plants.

Hardwood Cuttings

Not many greenhouse plants are propagated by means of hardwood or mature wood cuttings. Whilst giving Bougainvillea a prune up in February it is possible to root 10—13-cm (4—5-in) sections of mature wood, cutting below a node at the bottom and above at the top. These want to be kept at 13-15°C (55-60°F) and should root within two months.

Stem Cuttings Sections of stem with or without leaves can be used as cuttings.

Dieffenbachia and Dracaena which have become straggly and only have a few leaves at the top can be treated in this way. The best stem area is not the really woody area at the bottom or the spindly bit at the top but good average middle growth. Take a sharp knife or secateurs if you must (they can have the effect of squashing) and cut the stem into lengths of about 5 cm (2 in) each containing at least two nodes. These can then be inserted either horizontally or vertically into cutting compost. Do not forget to prune the original plant down to a small stump as it will shoot again if placed in a light position.

Stem cuttings of Aphelandra require only one node. Cut just above and below this, then if faint hearted take one leaf off (they grow opposite) and insert the cutting into compost so that the axil between the leaf and stem where the potential shoot will grow from is pointing upwards. The confident can slice the cutting lengthways so that each half contains one leaf and half the node. They are then treated the same, each retaining its leaf. When the container is in its final place and watered in make sure each cutting is well firmed.

Fiats can be treated similarly by cutting just above and 2.5 cm (1 in) below a node. There will only be one leaf as they are alternately arranged. Insert the cutting with the axil pointing upwards. To do this it will be necessary to roll the leaf, securing it with an elastic band, and tying it to a stake to balance it. It is necessary to keep these leaves on as there are insufficient reserves in the stem to allow the cutting to root and grow. I once managed to grow ten new plants from one 2-m (7-ft) Ficus ‘Black Prince’ using this method.

Root Cuttings

There are not many greenhouse plants that can be propagated by root cuttings. However, with Plumbago rosea this is the best method and gives better results than ordinary shoot cuttings. Take a mature plant out of its pot and find some well developed roots. Do not expect them to be particularly fleshy. Cut off sections 2.5-5 cm (1-2 in) long and plant them horizontally 6 mm (½ in) below the compost. It will take up to two months before any sign of new plants is seen but they will then grow rapidly.

Toes

Did you know that plants have toes? This is the name given to large fleshy roots which usually form towards the bottom of the pot and can be cut off and planted to grow new plants. Aspidistra and Cordyline are the main toe bearers. Pieces 2.5-5 cm (1-2 in) long should be cut off and, as for root cuttings, planted just under the surface of the compost. Each will often give rise to two or three new plants. It is best not to put these in a propagating case but keep them warm.

Leaf Cuttings

There are quite a few plants whose leaves or parts of them can be used to generate new plants. Begonia rex, B. masoniana and others including the Caribbean hybrids are examples. Take a good healthy leaf from Begonia rex and place it upside down on a firm surface. Make cuts across all the major veins then place the leaf veins down on to moist cutting compost. If necessary weigh the cut veins down with small pebbles to make contact with the compost. Placed in a warm humid place, small plants will grow from the cut veins. Alternatively, postage stamp-sized pieces of leaf can be cut each containing a piece of main vein. These are laid down on to compost and should all produce at least one new plant. I have heard of their being inserted upright but this method did not work very well for me when I tried it. B. masoniana is a little more difficult and more reliable results can be had by cutting triangular-shaped leaf pieces each of which contains a section of the main part of the leaf from which all the veins radiate. These are inserted upright.

One method of Streptocarpus leaf cutting is to lay the leaf down and make cuts along each side of the midrib which is then thrown away. Each long piece of leaf is then inserted with the cut ends of the veins downwards. New plants should grow from most of the cut ends. Alternatively, leaves may be cut transversely so that sections 5 cm (2 in) long are made. These are inserted upright and are probably a little more reliable though less prolific than the first method.

Saintpaulia are well known for their ability to produce new plants from leaves. The roots grow from the leafstalk so whole leaves should be cut off with at least 2.5 cm (1 in) of stalk attached. They are then either inserted into compost or water. Try placing aluminium foil over a jam jar so that the leafstalk is pushed through the foil into the water while the leaf sits on top.

Peperomia caperata also roots from the leafstalk but I prefer to insert the cuttings so that the leaf is just in contact with the soil. Leaves of P. argyreia can be cut in half and the tip half inserted upright from which new plants will grow.

There are many succulents, notably Echeveria and Sedum, which will root from leaves pushed into the soil. They are almost a nuisance. If anybody has ever owned a ‘jellybean’ plant (Sedum pachyphytum) its characteristic leaves will fall off at the slightest touch and root almost anywhere.

Plantlets

Some plants have the obliging habit of producing small replicas of themselves on the mother plants. All we have to do is take them off and persuade them to grow roots. One of the best known must be Chlorophytum (Spider Plants) which send out plantlets which can even be pegged down and rooted before being severed from the parent plant. Saxifraga stolonifera (Mother of Thousands) produces small plants on runners. Asplenium bulbiferum is a fern which bears many small plantlets or bulbils on its mature fronds. They certainly are a short cut to sowing spores. Tolmiea menzeisii earns its name of Piggy Back Plant by growing a small plant at the centre of an old leaf. The best way of rooting these is to take the whole leaf off, cut it down in size and push it into the compost. Kalanchoe diagremontianum is the Mexican Hat Plant and produces small plantlets around the edges of its leaves which even grow roots before falling off the plant. This is another nuisance plant as the plantlets seem to grow everywhere except where you want them to.

Layering

There are not many instances where layering is regularly used as a technique for greenhouse plants. However, it will work for Lapageria rosea (Chilean Bell Flower). Place a tray of compost at the base of the plant and disentangle a shoot which can be brought down to the tray. Cut upwards into a node and peg this down into the compost. Unfortunately much patience is required as it can be well over a year before anything significant happens.

Air layering, however, has more application especially with plants like Ficus elastica which may have become too tall. The method is to decide at which point on the old stem you wish roots to develop and remove any unwanted leaves at this point to give access to the stem. With a sharp knife make an upward cut about 1.2 cm (½ in) long just into the node area but only halfway through the stem. Wedge this cut open with a small twig or a few strands of sphagnum moss. This area now has to be encased with a moist medium for roots to be formed. All the old books say the sphagnum moss should be used but this is not always available and well moistened cutting compost does just as well. Take a polythene bag which is open at both ends and bring this sleeve down over the top of the plant. Tie it securely below the cut and fill firmly with compost. Tie again above the cut. I find that black polythene is most effective. After a couple of months roots should have grown out of the cut and they can be felt through the plastic. When you think there are enough roots, open it up and have a look before cutting the rooted plant off and potting it up.

There are of course other methods of propagation but they will be dealt with under individual plants. The most important thing to remember is that no matter how good you are at the technical part of propagation it is the aftercare of the cuttings or seedlings which is ultimately responsible for their success. Think about the conditions that they need and make sure they are given them straight away.

26. June 2013 by admin
Categories: Tips and Advice | Comments Off on Greenhouse Propagation

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