Julianne Nicholson is terrific as the mom in ‘Janet Planet.’ What is she doing right?

For years now, in conversations I’ve had with friends and colleagues, the name Julianne Nicholson comes up and it’s praise and admiration all around but maddeningly little specificity from any of us about why she’s so good.

After winning an Emmy as Kate Winslet’s best friend and the stealth MVP of HBO’s “Mare of Easttown,” you heard lots of vagaries along those lines. She’s just so, I don’t know, you know, good! Honest. Natural. Something. That something is crucial to the title role in “Janet Planet,” the supple debut feature from playwright-turned-screenwriter and director Annie Baker.

Now 53, Nicholson plays Janet, a western Massachusetts woman raising her 11-year-old daughter Lacy (played by Zoe Ziegler) across a series of transitional clauses we call a life. The movie takes place in the hazy, birdsong-filled summer in 1991, as Janet bends her days in different ways around three different men, while Lacy navigates her own place on the planet of Baker’s title.

What I love about “Janet Planet” is its devotion to the ambiguities filling the space between emotional extremes in any mother/daughter or parent/child relationship. “What Julianne does so beautifully,” Baker told me, “is hard to describe because she’s doing five different things. She can hold four or five intentions at the same time as a performer. And you never know exactly what she’s thinking.” To Baker, “that’s what real life feels like. And it’s hard to find on screen, and so hard to find an actor with that kind of mysterious nuance.”

I talked to Nicholson on her final day of a four-month, Los Angeles-based project: “Paradise,” the eight-part Hulu series created by Dan Fogelman (“This Is Us”). Nicholson has done episodic television for 27 years and features for 26, plus a lot of theater and, early on, some modeling. Watching some of her early screen work, you’re aware of several things. She was always good, even in not-good material. Her fluid physicality — loose, spontaneous, easy-breathing — plays like the work of someone brought up with plenty of space, time and room to just be. (She was raised partly in rural western Massachusetts, 10 miles from where she made “Janet Planet.”)

And this: The mysterious nuance Baker mentioned may simply be a terrific actor listening, and responding, using instinct and precise, incremental choices as her divining rod, pointing to the root of a character. The following interview has been edited for clarity and length.

Q: So many movies have a way of making the mother in a mother/daughter scenario either completely noble or completely hideous, because everything in between is harder to make interesting. In “Janet Planet” it’s not like that. What did those in-between spaces require from you?

A: Those are what I found so deeply interesting about Annie’s script. On any given day as a parent, you can be the savior, the villain or both. That’s what parenting is! (laughs). But all those moments in between are the most interesting and beautiful and simple, really. That’s where most of our lives take place. I’d rarely seen that on screen, and it felt like something exciting to figure out.

Q: One line in particular I think is so damn good: the moment when Janet tells her daughter, Lacy: “I’ve always had this knowledge deep inside of me that I could make any man fall in love with me, if I really tried. And I think maybe it’s ruined my life.” You barely emphasize the drama inherent in that.

A: That line jumped out at me, too. Totally believable. It’s a jumping-off point for the audience to get to know Janet a little bit more. I’ll say this, too: My tendency sometimes on this film (Nicholson made it in the hot, hot summer of 2022) was for Janet to be warmer with Lacy. But Annie encouraged me against that. And I’m glad she did. It’s more interesting to see both the closeness and the distance between them. Clearly they love each other deeply but in this particular summer of their lives, this is where they are.

Q: When you were 7, you and your sister moved to western Massachusetts with your mother near where you filmed, is that right?

A: That’s right. Ten miles down the road. My stepfather-to-be joined us there later. We moved from Medford, about two hours outside of Boston. My sister and I used to take the Greyhound or the Bonanza bus every other weekend from one (household) to the other, depending on who we were living with.

Q: What was your dynamic with your mother at that time?

A: I remember very clearly being a little threesome. It was probably only for a year and a half or so, but my mom, my sister and I were a threesome. We changed apartments at one point. I think my mom was asked to leave the apartment we were living in, in Medford, because the landlords didn’t want to rent to a single mom. This was in 1978, and there were certain ideas about who was respectable and who wasn’t.

Then we lived in Newton in a great big house with several different characters living there as well. We were there about six months, this tight little unit. There’s a certain closeness, along with some blurry lines, of a single parent and children. The amount of time together is different. It’s a very precious time in my memory.

In Newton we were suddenly living in this house with no electricity or running water, so it was a big adjustment. But kids are adaptable. It didn’t long for us for that to become our life. It was pretty sweet. Live in the woods. Be bored. Stare out the window. Listen to birds. Take walks.

I can’t recall ever seeing a movie filmed in that specific, special part of the Pioneer Valley region. A month before we started filming I went there with Annie. First time in 30 years for me. There’s different air there. You can almost feel it in your mouth watching the movie.

Q: A film like “Janet Planet” has to work so much harder than it might’ve before the pandemic just to find the audience it deserves. The industry right now —

A: I’m concerned. I wish it wasn’t so hard to get a smaller-budget film made, and then get eyes on it. But the industry is changing how we take in — “consume” (makes a fleeting “yuck” face at the word) — our entertainment. I find it sad, and distressing. But I have to trust that there will always be people like Annie, and companies like A24 (distributor of “Janet Planet”), that will continue. And take risks. We all have to make an effort, though. I think every actor should be going to see movies in the theaters. Everyone in the industry. Because if we aren’t doing it, how can we expect it of people who aren’t making movies?

Q: So what’s next for you?

A: I just finished “Paradise,” and I did a series for the BBC called “Dope Girls.”

We just moved to England, so I’ll be going home for a while to be with my family. (Nicholson has been married to actor Jonathan Cake since 2004.) The move came out of different reasons. Our kids were about to start high school. We lived in Topanga Canyon (outside L.A.) which was a big fire hazard; we’d been evacuating regularly. So, you know. Family. Life. Politics. It just felt like a good time to move. And I think we were right.