There's an old adage in project management that you can only ever achieve 2 out of these three desirable outcomes: Cost, Quality, and Time. In other words, there's always a trade-off, and something has to give.
It's a bit like that with blogging. Until you have got a good rhythm you'll likely need to choose two of Quality, Quantity and Time.
If you're creating highly-researched 3000 word cornerstone tomes then the number of posts you make is going to be lower. Highly-researched, well-written 1800 word cornerstone tomes will take even longer.
Once you've found your voice and know your audience your writing will be easier and be quicker, and you'll be able to meet all three outcomes.
Until then -
When inspiration strikes: write, write, write. Stack up content and drip-feed it on your blog when you're shorter on time.
If you get an idea for a blog, add it as a draft or jot it down in a notebook (I indulge with a Moleskine notebook for this. They're more expensive than a WH Smith own-brand pad, but ideas for content are valuable and should be treated as such). You can pad it out and publish later.
The 'ideas' well should never dry up if you're passionate and knowledgeable about your niche. If you 'um' and 'er' about what to write, step away from the 'New Post' page and go and do some reading, talk to people, look at some photos, reminisce, see what posts get good feedback or many visitors... and only write when you've got a good idea.
Writing is far easier and far more fun that way.
