Rose doesn't open fully

[Higgs Boson]

Here's a pic of a rosebush that bears abundantly, but most of the blooms don't open fully. What causes this? I'm in Zone 8, So. Calif coastal.

TIA

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[David E. Ross]

The roses with brown petals are afflicted with a fungus, most likely mildew since you are near the coast.

However, many roses never open fully. Only singles and semi-doubles open fully.

True doubles generally keep opening until they fade. But they have so many layers of petals that they do not show their centers until the petals start falling.

[Higgs Boson]

That would seem counterproductive in terms of fertilization. If the insects can't get at the germ material, how can they carry it elsewhere?

HB

[David E. Ross]

Most true doubles are hybrid teas. The were developed by a person cutting away all of the petals from a mature flower of one variety and then collecting the pollen. Then that person cut away all of the petals and stamens from an immature flower of another variety and then immediately tying a small paper bag over what is left of the flower.

When that second flower matures, the bag is briefly removed while the pollen from the first flower is applied. Then the bag is again tied over the flower. Eventually, a rose hip (sometimes called a pip) forms with seeds inside.

The stamens are removed from the second flower to prevent self-fertilization. The bag prevents stray, unknown pollen from fertilizing the flower.

Notice that NO insects are involved. Also notice that a failure of a flower to open completely has no impact.

Wild roses tend to have single flowers, which open completely. Heritage and species roses tend to open completely even if they have double flowers.