More information about plants in Plant of the Week

Magnolia Grandiflora

Magnolia Management

Planting and Growing Magnolias:
Magnolias are some of the first trees to lift the veil of winter with their fresh and sometimes vibrant flowers gracing bare branches in spring. With a little care and planning they are versitile plants which can form the backbone of any garden.
Magnolias come in two basic types:
Evergreen varieties which mainly have flowers of white and cream, but if michelias are included here, there is an increasing range of sizes, some with purplish tones in their flowers as well as perfume.
Larger growing types are mainly Magnolia grandiflora selections, but Magnolia delavayi is a bold foliage plant with interesting flowers that resemble ice cream cones. Michelia doltsopa 'Silver Cloud' is particularly spectacular in July and August, and its prolific cream, spicy scented blooms give the garden a lift at the end of winter.
Smaller growing types include Magnolia grandiflora "Little Gem', which eventually get as big as conventional grandifloras, but takes a bit longer. It flowers more freely than other M. grandiflora selections and makes a good container plant. (cream) and Michelia figo(the "Port Wine Magnolia") are good perfumed species which are suitable for the smaller garden.

Deciduous varieties which cover the greatest range of variations in tree size, flower colour and shape.
Smaller growing types include M. stellata which are commonly known as the "Star" Magnolias due to their many petals. Magnolia stellata selections come in white and shades of pink. For deeper coloured dwarf magnolias M. liliflora Nigra is hard to beat, with more lily shaped flowers in a rich reddish purple. This form has been used to produce hybrids such as 'Ann','Betty', 'Ricki' and 'Susan'.

Magnolia x loebneri "Leonard Messel" is a larger growing M. stellata hybrid with typical starry flowers and the richest colloured purplish pink flowers of any of the stellata types. It is well worth a place in any garden and flowers for 4-5 weeks when established.
Larger hybrids with flowers up to 35cm across in the case of Magnolia x 'Atlas', are quite spectacular on bare branches in spring. Selections with white, pink, purple and reddish purple are now available.
Magnolia x 'Atlas' 

Yellow magnolias are catching on with 'Koban Dori' ("Golden Plate Bird" in Japanese) being the only small growing selection and x 'Yellow Fever' and x 'Elizabeth' growing to timber trees, but producing creamy yellow flowers on bare branches in September. The yellow hybrids are best planted to be viewed with the sun shining through them from behind and highlighted by a dark background, such as a building, a hedge or even a hillside.

Planting:
When planting magnolias dig in as much compost as possible and work the soil in an area twice the diameter of the root ball of the plant. Place the plant in the hole then put in a strong stake before back filling so that the roots are not damaged by putting it in afterward.
Magnolias like a cool root zone so a good mulch after planting will pay dividends. Watch the plant does not get too dry in the first season since magnolias spend the first year from planting getting settled in. If they get too dry they will tend to sulk.

If there is some concern about bad drainage, plant your magnolia in a slightly raised bed so it does not sit in a pool of wet soil. If you want to plant a magnolia near water, make sure the plant has 40 - 50 centimetres of well prepared and aerated soil above the water table to get itself established in. It will appreciate the close proximity of the extra water, but let it decide how close it wants to put its roots to it.

When transplanting a magnolia it is best to move as large a block of undisturbed soil as possible and the resulting stress will be proportionally less. If the root ball gets disturbed or even shaken out completely, then the plant will benefit from a reduction of branches by at least a third. Evergreen species should be root-pruned in autumn before tranplanting, and deciduous species are best moved when dormant, though they can be treated as evergreens and root-pruned for shifting in the autumn, as long as their growth has matured when the root-pruning process starts. If you have to move one in growth, trim out all the active growing tips, and if possible spray with an anti-dessicant spray at label rates.

Pruning:
Magnolias generally dont need a lot of pruning, but if you understand their growth habit they may be modified to fit a smaller growing space than they would normally require. With careful selecting of varieties, pruning will also increase the production of pickable flowers.
All magnolias go through an establishment growth phase which is characterised by open upright growth with few flowers followed by a maturing twiggy phase as the growth slows down to produce a more horizontal, tiered framework with many more flowers. From time to time they will also send up strong growths from the base or the main branches. Some varieties do this more than others, and with grafted plants it is important to know whether these shoots are from the rootstock or the grafted portion. Leaf form is a good guide, but if there is any doubt, these shoots should be removed. These shoots can produce a secondary leader with a very tight fork, which if left to develop can create a weakness that will sometimes split out in strong winds and damage the tree severely. Newly planted magnolias will often produce this type of strong growth in the second or third year from planting, showing they have settled in and are ready to build their branch framework. When this happens you can either leave the strong growth to develop a vertical trunk with a more even framework than the original plant, or if you are happy with the original structure, you should remove them as soon as they appear.

Redeveloping the framework takes about three years or more but it is well worth the effort to enhance the elegant stature of the tree as it matures into a formal framework.
In the first year the older part of the tree should be pruned by about a third to encourage more vigour into the new shoot, and each year after that the old framework should be pruned to allow the new structure to develop evenly. In the second or third year, the old portion may be removed completely, once the new frame is about half the total framework of the tree. Be sure to seal the cut with pruning paste to prevent rot entering.

When older trees produce these vertical shoots they will grow upwards till they reach the canopy then branch out and settle down to flower. If the tree needs to be reduced in size then it can be pruned back to these shoots and pruning paste applied to seal the cut. These shoots will mature faster when the tree is pruned to give them more light.

The overall size of a magnolia can be limited by annual pruning immediately after blooming. As long as the twiggy flowering wood is left and the long shoots and any dead wood is removed, the flower display is maintained on a compact tree. On some varieties this annual prune encourages the tree to produce stems which have up to six or eight flowers spaced along them, Apollo, Iolanthe, Denudata and SanJose being among these types.
Alternately magnolias may be limbed up to make shade trees or even timber trees. It is a little more difficult to limit the bushier types to a single stem, but as long as you remove undesired shoots as soon as they appear, they will respond to training. 
 
Checking a magnolia flower is at the right stage for picking: This illustration shows the stigmatic column in the centre of a magnolia flower.
The upper portion that looks like a pineapple top is the stigma which shows a slight crystaline look, which means it is still receptive to pollen. The lower portion of purple and white striped anthers are still tightly closed.
They will not open until the lobes of the stigma fold upwards, which means to set seed a magnolia flower must receive pollen from another flower.
 
Annual pruning also produces flowers with straight stems suitable for picking. Some varieties respond better as cut flowers than others, with Heaven Scent lasting up to nine days in a vase. We often enjoy the beauty of magnolias inside by picking them when they are first opening,with at least one or two tepals unfurled. At this stage the top of the stigmatic column in the centre of the flower should still have a glistening look about it which means it is just opening and still female receptive. They should be put into water as soon as they have been cut, and if in not too hot a place, will last a week or more in water, depending on variety.

Pest and Diseases:
Magnolias are generally trouble free garden plants. The commonest problem is bacterial leaf spot which appears on the new growth in the earlier part of the season while conditions are warm and moist. Some varieties are much more prone to it than others. This is best controlled by a copper spray in winter, followed by copper sprays 2 - 3 weeks apart at summer strength while the plants are putting on their spring growth. If you grow potatoes or tomatoes and spray to prevent blight, just mix up a little more spray and do your magnolias if this is a problem for you.
Another problem is borer. Keep an eye out for the tell-tale dark holes on the stems, which sometimes weep if water is getting in, and the accumulation of white frass, which is actually fine "sawdust" that has been excreted by the grub.

A problem which occurs sometimes is a blackening and death of the stems associated with a strange fermenting smell when examined closely. Sometimes half of the tree may be infected, but very rarely is it completely fatal. Again, some varieties are more prone than others, and unfortunately it is often grafted varieties where seedling rootstocks are more susceptible to the root problems. This problem is generally associated with poor root conditions as a result of bad drainage or root damage, as well as low fertility. Good soil preparation and site selection as well as adding as much compost as you can, followed by annual mulching will avoid this problem.(see planting hints)

Look at the magnolias growing in your area and see which types are doing well. The friendly staff at your local garden centre will also be able to help you choose the one that will bet suit your situation.
 
This article was kindly supplied by Vance Hooper http://www.vanplant.co.nz