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Q&A - Question & Answer about gardening

Q: Eric Bray – My old camellia trees (at least 30 years and 12 – 15 feet high) have grown very yellow leaves this year, although they are full of flowers.  I presume they are hungry, but what is best to feed them with? Thanks.

A: If your camellias have thrived so well so far, this looks like a recent problem.   The soil may have got too soggy over the last year, which was a really wet one, and this would make it difficult for them to absorb the nutrients they need to keep them healthy.   Try feeding them weekly with an ericaceous plant tonic.   You will need to apply this in liquid form over a large area to make sure the mature roots receive what the plant needs.   It could take several months before the new shoots start to look healthy.

Q: Margaret Savage – My Gleditsia ‘Sunburst’ tree which I love is not budding yet, and a lot of the branches are brittle and snap off when pulled. Am I losing it and if not what can I do to revive it please?

A: The good news is – my ‘Sunburst’ isn’t budding yet, though I know from experience it’s still alive.   The bad news is, Gleditsia ‘Sunburst’ can die back seriously until it gets really well established, as can all related trees, like Robinia ‘Frisia’.   In addition, these trees have very brittle branches, which makes it difficult to decide at this time of year whether they are dead or just dormant.   In view of the late spring, I would wait at least another month and see if it produces shoots further down the branches, or even at the top of the trunk/stem.   If not, it’s probably dead.   If you decide to replace it, it might be worth choosing a more sheltered spot.

Q: Ricky Berg – I bought a Laburnocytisus Adamii from you a few years ago & am very happy with it. It’s going to flower this year for the first time, very excited to finally see one in bloom! I’ve always wondered if it were possible to develop different colour variations of this tree by using other alternative coloured broom, such as white. Would that work?

A: Laburnocytisus ‘Adamii’ is what is known as a graft-chimaera between two species, both members of the pea family – Laburnum anagyroides (common laburnum), and a purple broom, Chamaecytisus purpureus.

A graft-chimaera is technically not a hybrid between two species, but a mixture of cells, each with the genes of one of its parents.  After the grafting process, the tissue of one plant grows within an outer covering of the other one – in this case, the laburnum forms the central core, the outer layer being the broom.   The effect is that most of the branches have laburnum-like leaves, with three leaflets, but there are, in addition, many broom-like shoots, especially on younger specimens, also with three leaflets, but shorter and a darker green than those of the laburnum.

The tree flowers in late spring or early summer and usually some branches produce long, yellow, laburnum-like racemes, while others produce dense clusters of purple flowers resembling those of the purple broom parent.  Sometimes branches will also produce short racemes of coppery-pink flowers on short (8–15 cm) racemes.   As the tree ages, however, the yellow laburnum flowers generally predominate.

This curiosity originated in the nursery of M. Adam near Paris in 1825, and is considered to have arisen as an accidental graft.   The purple broom is normally a low-growing plant and the grafter possibly thought by grafting it onto a straight stem of an upright related species (i.e. the laburnum) he could create a small, semi-standard, weeping tree.   Therefore, it is certainly likely that other +Laburnocytisus could be developed in the same way using different species of laburnum and broom.  

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