Spikes on Den. aggregatum blasted!
 

My Den. aggreatum got 7 spikes this year. I was SO excited since it has only ever gotten 1-3 before & most of those I accidentally broke off. Anyway I watered after they were about 3-4" and almost all of them have blasted now. What did I do? Water too soon, water too much or not enough? I only gave it a little water (when I water it normally I usually water every day & quite a lot) Any ideas so I can avoid this next year, please.

I'm not sure what happened in your case, unless the water or air was too cold. I used to jokingly call that orchid Dendrobium aggravatum.

Might be a temperature problem…these dendrobiums want mild to warm in winter, but much cooler nights they can go as low as 45F.... And they need higher light in the winter, too.
Regular watering regimen must resume when flower buds emerge=it means the winter rest is over...so what you did was good....but don't wet the spikes and buds =that might be also a factor why it blasted....

Our temps have been up & down in wide swings here. My growing area is heated but maybe it got too cold after I watered. I water early so things can dry but that is all I can think of. I wish I knew so I could avoid this next year.

Try to invest in a humidifier..... even if you water the roots it still need atmospheric moisture(your grow zone is very dry in winter)....these plants need at least 60% humidity when the dormant period is over....