I have a lot of buzy lizzies in the garden but some are failing

It could be too much sun, but if only a few out the whole lot are doing it then probably not. At the nursery where i work we grow them in shade from february in greenhouse untill we sell out.
There is a mildew thats has recently been attacking Buzy lizzies in many nursery magazines a letters from suppliers, may be that, but not sure how it comes about, best to remove manky leaves and fallen ones and bin or burn. Same with badly affected plants.
Dont think you can grow them again in same place next year as spores stay in soil and it can build up over time.

I usually grow most of my busy lizzies in pots and I seem to have more control of them than in the ground. Every now and again, when they are in flower, I hold them upside down on top of the compost bin and give them a bit of a good shaking as then all the loose 'bits' fall off into the bin.

Check among the roots of the sick ones to see if you have vine weevil, little white grubs which eventually cause the plants to keel over.

hello, if you go to the R.H.S. site and type into the search bar bizzy lizzies you will find your answer on the fourth link down,you are looking for "impatiens downey mildew", i had the same problem last year when i lost all my bizzy lizzies and it took me ages to find out why, good luck

The answer is as follows:-

Impatiens downy mildew is a fungal disease that causes yellowing leaves, leaf loss, and death of bedding Impatiens, commonly called busy Lizzies, during favourable wet weather conditions.

Impatiens downy mildew is a disease caused by the fungus-like organism Plasmopara obducens.

It was found for the first time in the UK in 2003 and is likely to have arrived on imported commercial propagation material (seed or cuttings). For a short time statutory action was taken by Defra against confirmed outbreaks of the disease, but this approach was soon dropped. The wet summer of 2008 triggered the most widespread outbreak of the disease so far, with many gardens, nurseries and local authority displays affected. Attacks are most likely in summer, or spring in greenhouses.

Outbreaks of downy mildew have been confined to Impatiens walleriana, the common bedding busy Lizzie. No cases have been found on New Guinea Impatiens, Impatiens x hawkeri, or on the few species of Impatiens found growing in the wild in the UK.

You may see the following symptoms:

On leaves: Affected leaves turn yellow and are rapidly shed from the plant. A fine white fungal growth may be visible on the lower leaf surface, but affected leaves decay rapidly.
On flowers: Flowers are also commonly shed, and the plant is often reduced to bare branches with a small tuft of yellow leaves and flower buds at the tip. Severely affected plants will eventually die.
There have been some reports of variations in disease severity between different varieties, but these have yet to be confirmed.

Non-chemical control
Affected plants should be disposed of as soon as possible. Do not compost them. Ideally burn them or bury them deeper than 50cm (20in).

Because of the risk of soil contamination, rest affected areas from Impatiens for at least a year (some species of Plasmopara affecting other plants produce resting spores that can survive for several years).

Where infected plants have been grown in containers, replace the compost and wash and disinfect the container if you intend to grow Impatiens in it again the following year. The disease is specific to Impatiens, so any other bedding plant can be grown without risk.

Unfortunately, growing Impatiens in another part of the garden will not guarantee freedom from infection, as the disease may well arrive again as airborne spores from infected plants growing elsewhere. There is also a risk of purchasing infected plants, as this type of disease often has a lengthy ‘latent period’, when plants are already infected but not yet showing obvious symptoms.

There are no fungicides available to amateur gardeners for the control of this disease.

Downy mildews are a large group of plant diseases caused by microscopic fungus-like organisms related to the pathogen that causes tomato and potato blight. Despite a similar name and certain similarities in symptoms, they are unrelated to the powdery mildews.

The disease is spread by spores produced on the underside of infected leaves. These spores are splashed by rain, and are also carried for long distances on the wind. Extended periods of leaf wetness are required for spore production and infection, so severe outbreaks of downy mildew are only likely to occur during wet summers.

The airborne spores remain viable for just a short time, but it is thought that the fungus can also produce a second spore type (a resting spore) within the affected plant tissues. These resting spores are much more resilient, and are released into the soil as the diseased material rots down. They are likely to survive within the soil for an extended period.