are you a native English speaker?

He's not, he speaks Russian natively. He hasn't been seen on this site for quite some time.

I was wondering because that's not a very good translation.

Do you find the continuous tense dubious? But there's got to be some way to keep the difference between убрать & убирать in translation, though.

We would only use the continuous here if another action happened simultaneously: Yesterday morning, I was harvesting potatoes... WHEN I heard a crash on the main road -or- AND all of a sudden it started to rain torrentially. However, unless someone specifically asks what you WERE DOING, then it doesn't really make sense. A: Where were you yesterday at 9am? B: Yesterday I was harvesting potatoes all morning.

The fact is that the only natural way to translate the Russian imperfective describing how one spent past time - with the simple past and perhaps a time element: Last night I read for two hours. My girlfriend called me and we talked for two hours.

In this last example, you may hear some Americans say "My girlfriend called me and we were talking for two hours." as a colloquial device to emphasize the length of the conversation, but it's not standard and to me it sounds very "young."

But then I have an idea: you insert the word 'busy' and get "yesterday morning I was busy harvesting potatoes", which seems perfectly cool and rightly emphatic.

Yes, that's true. But the question remains: if the point of the sentence is part of the potatoes were rotten, why is he telling me what he was busy doing? In other words there can only be one theme: the rotten potatoes or what was he doing yesterday?

The second sentence looks like an afterthought to me, so it may well have a different theme. There is no "by the way", but that's not a must, is it? Just a pause in speech.

ok :)

So then, assuming "yesterday in the morning" is fine, what could be done is adding the "busy" after "was", and then we'll be good, right?

It should be "yesterday morning" unless he's contrasting morning with another time of day. Adding "busy" just reinforces the imperfect interpretation, but then it doesn't go anywhere... starts going on about the state of the potatoes and the listener is still wondering "well... what happened while you were harvesting potatoes?

If the potato sentence was meant to be an afterthought, he would have to continue the story, because he has already activated a storyline in the listeners mind: [storyline]: "Yesterday morning, I was harvesting potatoes. [parenthetical afterthought]: Because of the rain they were partly rotten. [continuation] All of a sudden I heard a loud crash across the field.

I thought on this site, you were only allowed one sentence at a time anyway?

Well, no, actually you can add multiple sentences (monologues and polylogues alike) in one item. It's good, being more diverse.

I see then. Still, it feels rather silly to me that in this case there isn't a way to concisely distinguish between a complete and an incomplete action in English.

If it were that simple, English speakers wouldn't have the trouble they do assimilating aspect in Russian. The fact is you can disambiguate these aspects in English, but since English isn't an aspect driven language, the use of the imperfect has to be validates by an external prompt: either someone wants to know what exactly someone was doing and why -or- as an ongoing action that serves as the backdrop to another simultaneous action. That's why the "story" falls apart in this example - because the listener thinks that he was drawn into the "harvesting" because something interesting happened during that time... AND THEN HE SAYS THE POTATOES ARE PARTLY ROTTEN!!! :)))

This is why I asked if RU was a native.

Conversely, when I started studying Russian (three years ago), I couldn't understand why it was possible to say "Вчера вечером я читал книгу." In our tense system, when you did something last night, it's the simple past, no matter how long it lasted or if you finished UNLESS something else happened while you were doing it - then you have to use the imperfect in order to bring the speaker into the story.