Weird Lavender Flowering behavior

MikeP2 says:

If you would please have a quick look at the attached photo. I have a problem with my Lavenders that seems to repeat this year. Normally I would expect the flowers to be open for many weeks in full bloom but many of my plants have the following behaviour:

Only a few of the calyx randomly open, bloom briefly (looking normally) and then the flower wilts away in no no time, therefore the whole spike is never in bloom! It looks kind of sad and worst with the white varieties which look grey with the odd bright white flower! I had great hopes that this year it might be back to normal.

The picture shows the Little Lady variant which is looking quite full despite of the problem. Worst really seem the white varieties that should be bright white but never show much flower at all other than the odd flower.

To the background, all plants are grown on a slope. Most of them are 2-4 years old, should be exposed to th sunlight when the sun is shining. They have never been artificially watered once established, never had any fertiliser. The soil is mostly ordinary top soil mixed with smaller stones, nothing special. Rosemary beetles have been spotted over the years but an effective reward scheme with the children (20p/beetle) has largely eradicated them. There are about 10 lavender varieties.

Would you have any idea what might cause this problem?

Thanks, Mike

(Picture shows issue on Little Lady variety)

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