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Cultivation of Magnolias

Magnolias are easy to grow and relatively pest free. Once established they need the minimum of attention.

The perceived problems of size, first flowering and frost damage – Magnolia myths.

The three things which most frighten people about magnolias is firstly their ultimate height as tall trees, secondly the length of time which they take to produce their first flowers and finally the susceptibility of the early flowers to frost.

Although the 80-100 feet tall Magnolia campbellii, sargentiana robusta and mollicomatas which produce such a spectacle in February and March in Cornish woodland gardens can appear a bit daunting it must be remembered that magnolias grow much taller in Cornwall than they will in other parts of the country where rainfall is much less. There are several species which are smallish shrubs and which are entirely suitable for smaller gardens or even tub growing (e.g. Magnolia stellata, M. lilliflora Nigra and several crosses between these two species - ‘Susan’, ‘Randy’, ‘Ricky’ and ‘Jane’). Most varieties of Magnolia soulangeana are excellent garden plants which will become large shrubs but can readily be pruned. Not all magnolia species and varieties are therefore just the preserve of large country gardens although tree magnolias should clearly not be grown too near houses.

If you grow tree magnolias from seed they may well take 10-15 years until they first flower. In one instance at Caerhays a magnolia took over 40 years to flower. However, most magnolias sold today are GRAFTED plants. This means that the long wait until first flowering can be readily avoided because of scion material used to make the graft comes from the flowering tips and branches of existing plants. Some grafted tree magnolias will even flower while still in their pots but it would be very bad luck for a grafted plant not to be flowering away within 3-5 years from planting. This criticism of magnolias is also therefore a misconception.

Clearly any plant which comes into flower in February or March runs a very real risk of having its flowers frosted. Even in the mild Cornish climate this can and will happen some years. However magnolias adapt to the climate of their surroundings and a Magnolia campbellii in Yorkshire might only come into flower in April in a cold spring. Certainly it might well still get frosted but it is not necessarily going to happen very often.

If you live in a frost pocket or in the North of England or Scotland you need to select magnolias which do not flower until mid April and mid May. There are plenty of taller growing magnolias to choose from and ‘Serene’, ‘Iolanthe’, ‘Caerhays Surprise’, ‘Atlas’ or ‘Apollo’ are all good choices. Additionally most Magnolia Soulangeana hybrids do not come out until May.

So select the variety for your area and stop worrying too much. If our current run of very mild winters continue the risk of frost damage is minimal and magnolia flower buds are very well protected by two furry outer coatings which only drop as the bud opens.

Just because the flowers can occasionally get caught by frost does not mean that magnolia trees and shrubs are not totally hardy. They most definitely are so put these three popular myths behind you and treat them as the uninformed misconceptions that they are.

Soil conditions

Back to Top Magnolias perform best in a loamy, well drained soil but rich in organic matter. You can make an easy contribution to the organic bit by putting plenty of compost or well rooted manure into the planting pit and keeping the plant regularly mulched. Magnolias are surface rooting plants which respond well to mulching.

A slightly acidic soil is best. Lime or alkaline soils are more difficult for magnolias but, while nothing will grow on pure chalk, many Magnolia stellata and Magnolia soulangeana varieties grow perfectly well on ph’s of 7 as opposed to the optimum 5.5 – 6.5. If you look at the magnolia collection in Windsor Great Park and in the Savill Gardens it is hardly an acidic soil area but with the application of peat and fertiliser you would not know it.

Location

Back to Top Magnolias prefer to be grown in full sun but will tolerate dappled shade providing there is plenty of room for them to grow and expand without becoming misshapen and ‘leggy’. If magnolias are squashed or competing for light and space with other trees and shrubs they will not flower well.

Although, as explained, magnolia trees and shrubs are totally hardy it is foolish to plant them in windy or exposed areas where not just the flowers but also their large leaves can get damaged unnecessarily. Magnolias hold their leaves long into autumn which accounts for their phenomenal growth rates. However it makes the trees vulnerable to heavily leafed branches literally splitting off or breaking in strong winds. Some shelter is therefore adviseable.

If you live at the bottom of a hill or a deep valley try to avoid planting your magnolia in the very bottom of a frost pocket. Cold air and frost moves downhill and concentrates in valley bottoms so try to plant uphill if you can.

Pests and Diseases

Back to Top Magnolias are relatively pest and disease free in comparison to say rhododendrons. However, as usual in nature, there are a few things you can do to avoid disasters. The majority of magnolia casualties soon after planting can be attributed to one of the following problems:-

• Biggest Problem 1 - When you plant a grafted magnolia the old soil level in the pot must marry up and be level with the soil level in the ground. If you bury the rootball or potfull more deeply you will very probably end up covering the graft with soil. This will soon cause the graft to become infected and the plant will die even if the rootball survives. You can easily achieve the same result by mulching too thickly and again covering up the graft. For more tips on how to plant trees and how to treat grafted plants please refer to the Planting Advice Section of our main website.



• Biggest Problem 2 - Very often we are told that a customer’s magnolia has come into leaf and then suddenly the leaves have vanished or gone brown or have turned into leaf skeletons. This is the work of small slugs which live in the soil and only emerge in damp weather usually overnight to take their fill of young magnolia shoots and leaves. Snails may help out too but you seldom actually see them at work. Prevention is possible but in extreme cases there is no cure after the event. In April and May as the leaves unfurl you should add slugbait to the base of the plant and repeat this after rain for a couple of weeks until the leaves are fully formed. After 2 or 3 years of growth the plants can usually withstand a slug attack but not before their root systems have formed properly.



• Biggest Problem 3 - The sap in magnolia stems and bark is highly pungent and therefore especially attractive to rabbits. If you planted out 10 trees only on of which was a magnolia, it is a near certainty that the magnolia will get ring barked by rabbits first. You may say that you do not have a rabbit problem but it only takes one! The solution is to put a spiral guard around the main stem but some magnolias have lots of side shoots which makes this difficult. Better still is to make up a circle of 1 inch wire netting which is at least 2 1/2 feet tall and surround the plant with this. This will afford genuine rabbit protection. Happily deer do not seem to like magnolias as much as rabbits at least with us.

Hybridisation of Magnolias

Back to Top Making your own unique cross.

Anyone can hybridise two different magnolia varieties when they are in flower to create a new hybrid (or rather lots of new hybrids) of your own.

Cut and take a flower from one magnolia plant, the ‘Pollen Parent’ and spread the pollen exuding from its stamens onto the stigma (or female reproductive part) of the ‘Seed Parent’ flower on the other magnolia plant.

Then remove all the tepals (petals to you and me!) from the ‘Seed Parent’ flower as well as the male pollen bearing stamens. This should ensure that the ‘Seed Parent’ will not get visited by other winged insects carrying other different pollen as, without the petals, there is nothing to attract them. It will also avoid self fertilisation whereby the flower fertilises itself with its own pollen.

You then clearly mark the twig on which your cross has taken place and hope that the stigma will grow and develop into a seed pod with viable seeds which represent your unique cross. If it does, and there is no guarantee at all that it will, then the seed can be collected in October or November when the seed pod splits and the bright orange individual seeds can easily be seen.

How to grow these magnolia seeds is described later in this article.

Propagation

Back to Top Magnolias can be propagated in three ways:-

• i)From seed – the majority of magnolias are propagated in this way.
  
  
• ii)From cuttings – in reality only the smaller growing shrub or soulangeana varieties will propagate from cuttings. Perhaps only 15-20% of the magnolia varieties grown in the UK can be propagated in this way and, even then, this is not something which the amateur will easily succeed in.
  
  
• iii)By grafting – the majority of tree (sized) magnolias are propagated by grafting scions from named magnolia varieties onto another seedling magnolia rootstock. This is a difficult and complicated procedure which needs specialist greenhouse equipment and is therefore something which is best left to the experts.
  
  

We will therefore concentrate on growing magnolia seed. Details of each picture are given below



Figs. 1 & 2. When you have collected your long ripe magnolia seed pods and their bright orange seeds, remove the seeds from the pods and store them in a mouse proof container. Do not put them in full sun or somewhere hot such as a radiator but do not put them somewhere damp where they will rot either. A sealed plastic box is fine and do not be worried if the seeds grow a little mould.

Figs. 3 - 6. In early March prepare a box or tray of say 18” x 12” x 3” (deep) with a mixture of soil, peat/compost and a little sand. The tray or box must have good drainage. Take each seed and rub it between finger and thumb, or wash in washing up liquid, to remove the sticky orange skin around the seed which in the autumn was designed to make a bird or rodent see and eat it. All you are doing is what the animal’s stomach would have done to remove the seed covering. By March it will probably look more brown than orange but it still needs removing. If you do not do this your germination rates will reduce by 50-70%.

A box of the size outlined above will take about 40-50 individual seeds placed about an inch below the surface.

Fig. 7. Then cover the box or tray with a piece of glass to make it mouse and slug proof. This is essential!

Fig. 8. After 6 or so weeks you will see germination taking place but this will occur sporadically (hopefully) over several weeks and not all the magnolia seedlings will appear at once. The temptation to remove the glass is huge but be careful. Build a bit of a frame over the seedlings and keep the glass over the top. Again this will keep mice out but small slugs and snails can still be a problem.

Fig. 9. In hot weather in May or June put newspaper over the glass to shelter the young seedlings from scorching in direct sun. Once they produce their secondary and tertiary leaves this will not be necessary.

Fig. 10 & 11.If you have done everything right you will, by September, have a tray of seedlings which are variously between 4 and 12 inches tall.

Leave well alone while they are in leaf. However, when they shed their leaves and go dormant you can dismember the box or tray and separate the roots of the individual plants. Pot them on into 1 litre pots before they come into leaf and then again into 3 litre pots in the autumn.

Fig. 12.You then have a plant – perhaps even a unique hybrid of your very own – which should be big enough to plant out in the garden the next spring. Alternatively, if you are a magnolia breeder, you will have a perfect rootstock for grafting in the following year.

Click here to visit Caerhays Castle Gardens, where you can see Magnolias, Camellias and Rhododendrons in full flower each spring.

Fancy a luxury break? Recently renovated and beautifully decorated, this 8 bedroom mansion is a peaceful retreat for you and your friends on the Caerhays Estate. Click here.

Burncoose Nurseries: Gwennap, Redruth, Cornwall TR16 6BJ
Telephone: +44 (0) 1209 860316 Fax: +44 (0) 1209 860011 Email: info@burncoose.co.uk