Hawthorn Bonsai Flowers

How to make your Hawthorn, and other bonsai, flower

The new Bonsai Book for 2019 by Harry Harrington
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hawthorn bonsai shoot

Immature vegetative shoot of a Hawthorn bonsai extending

Encouraging a Hawthorn to flower

Trees need to reach a certain age before they will ever begin to flower. The age varies according to the exact species; some species will flower after just a couple of years, others, such as Hawthorn need to reach 15-20 years of age before they will begin to flower.

Feeding regimes high in phosphorous can help encourage more flowers on a tree that already produces flowers each year, (do not feed high nitrogen as it will encourage vegetative growth), but will not make a tree enter maturity and start flowering.

The procedure is first to gently slow the vegetative growth by allowing a Hawthorn bonsai to become on the rootbound side, if repotting and rootpruning is absolutely necessary (for the health of the tree), only rootprune lightly. Newly available space around the rootball encourages new rootgrowth and therefore new vegetative top growth. A confined rootball dissuades the tree from trying, or being able, to spread itself and remain immature.

Do not prune the tree hard, reduce the trunk or remove heavy primary branches. Doing so will result in vigorous vegetative growth, very much at the expense of flowering. New collected yamadori (wild trees) that may have flowered well for many years in the wild, will frequently stop flowering for many years after being chopped or pruned hard, until they re-enter a mature-growth phase. When a previously mature tree is in a vegetative/immature stage of growth, existing flowering spurs will simply open a rosette of leaves in the Spring but will neither flower or extend. Occasionally they will produce a vegetative extending shoot but this cannot be relied upon when trying to develop the branch structure of a bonsai. Bonsai that are still having their branch structures developed or are poorly ramified, should be 'completed' before encouraging flowering.

(On bonsai species that flower easily, the reverse is true, remove flower-buds to encourage more vegetative growth on trees in development)

Once the vegetative growth of a well-ramified and pot-bound Hawthorn bonsai slows down, pruning to contain the size of the tree naturally becomes more gentle. The tree begins to produce a new type of shoot that contains flowering 'spurs'. This is mature growth and is subtly different than immature, vegetative growth.

flowering spur bonsai

Two new shoots on a Hawthorn bonsai during the Summer. On the left a mature flowering spur, on the right, a vegetative shoot carrying just leaves.

Flowering shoots on a Hawthorn will have a thorn at its tip, as shown in the image above. These shoots should not be pruned, if possible, otherwise they may become vegetative. Flowering shoots that are left unpruned will produce flowering spurs from which flowers will emerge sometime in the future. Unfortunately with Hawthorn bonsai, encouraging flowers can take a few years to achieve. The thorn itself should not be removed for the same reason.

Importantly, vegetative shoots (without a thorn at their tip) should be pruned by pinching out their tip as they extend to stop them becoming too long rather than allowing them to extend fully and then pruning them back (which encourages further vegetative growth).

flowering spurs

Flowering spurs on a mature shoot in early Spring

The new buds emerging from flowering spurs in the image above have appeared on mature shoots that are a number of years old. These buds will produce flowers in approximately 2 months.

hawthorn leafbuds

Normal vegetative buds starting to unfurl new leaves on a Hawthorn in Spring

bonsai flower buds

A flowering spur on a Hawthorn beginning to open in Spring and revealing a cluster of flower buds.......

flower bud

4-6 weeks later, the flower buds are about to open........

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