Dendrobium Kingianum buds not opening, going brown

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It's fine to water them in winter. It does not inhibit flowering, nor damage the plants at all. Just don't fertilize after late Summer. Bud drop can be caused by not enough water, too low humidity, too high temperatures and thrips insect damage. Familiarize yourself with thrips. They may damage buds long before the damage is visible. Thrips may damage buds on many different genera of orchids.