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Paulownia - Growing Guide
Commonly known as ‘Foxglove Trees’
There is no tree as impressive as a blue flowering paulownia tree in late spring just as the leaves are emerging. Blue is one of those colours which is almost unique in a spring flowering tree and hence gardeners desire to grow them.
However, at Caerhays, we have begun to discover that there is more to paulownias than P. tomentosa. We have flowered P. fortunei, P. lilacina and P. fargesii in recent years. Since these three species all set viable seed we hope shortly to offer these exciting new trees in our mail order catalogue.
P. tomentosa grows very quickly indeed. New growths in young plants can grow 4-6ft in a single year. The ultimate height of these trees is 30-40ft with a spread of 20-30ft. They therefore need plenty of room to grow and a carefully chosen spot.
Paulownia have huge 12in long leaves and therefore need wind protection. They grow best in full sun in a warm spot in a fertile but moist soil. As very greedy plants they will grow just as fast as you can feed them up in rich soil and added compost or manure.
It is because they grow so quickly with succulent pithy new growth that they can be vulnerable to frost damage when young. Although perfectly hardy trees, when you tap the stem or trunk it sounds hollow. The tree has a pithy core in its trunk and, once the sap rises in spring and the leaves begin to emerge, hard frost can have the same effect as splitting in a frozen downpipe on your house. Plant them well up a hill or bank and away from streams or water which are frost pockets at the bottom of the valley.
P. tomentosa flowers emerge in April or May. In dry springs the flowers precede the leaves. In wet ones they can appear together. The individual 2in long flowers are fragrant and blue-purple on the outside with purple and yellow blotches on the inside. They are shaped like a foxglove in upright panicles of around 1ft in height when fully out.
The buds are formed in the previous autumn as spherical brown clusters which are easy to see.
P. fortunei has very beautiful flowers as well. They are lavender-purple or lavender-white on the outside and white or creamy white inside with dark purple spots. This species, after 20 years here, is nowhere near as large or vigorous in growth as other paulownias.
P. lilacina is hugely floriferous with us over several months. In a mild autumn the odd pale lilac flower with a yellow blotch inside can often be found. More flowers open in February and March on bare stems as single flowers rather than as panicles. The main flush of flowers is in March and April. Our eight year old plant is already 20ft tall with a similar spread.
P. fargesii has been shy to flower with us despite achieving even more staggering growth rates than P. lilacina. The flowers are a pale blue and the leaves larger than on any other species. These exponential growth rates may explain why it has been shy to flower.
Some paulownias will form suckers from where the roots rise above the soil surface. These can be dug and lifted. However all paulownia species are easy to grow from seeds sown in containers in the autumn spring. The young seedlings are very delicate and need to be grown in a frost free environment for a couple of years.