Job interview- when should I tell them I'm pregnant? And how should I dress?

I have an interview at a garden center on Monday, so the atmosphere is pretty casual. Should I dress casual for the interview?
And should I wear clothes that hide my pregnant belly?
I'm 20 weeks pregnant, due August 29- when should I tell them if I get the job?
Before I start? Or after a few weeks?
I'm not worried about legally, I'm just worried because its a family business and it would be awkward if their new employee is obviously pregnant and just not admitting it.
I don't plan on quitting when the baby is born. But I would obviously need off for a few weeks and then when I came back, it would be part time instead of full time.
Whats the proper etiquette in this situation?

Let's start with what you should wear. I think for any interview you should dress for success. I would say if it's more casual you should wear black dress pants and a nice blouse or something (don't go too casual - especially not in jeans!). Wear what's comfortable for you. You should tell the interviewer that you are pregnant and what your plans are. I am a Supervisor at my company and we brought in a woman that we didn't know was pregnant (you can't ask legally) and the whole reason we brought her in was to cover for a woman who was pregnant and going to be leaving on maternity. Turns out both of them were due at the same time so we really hurt with our productivity because she didn't come out and tell us. Fortunately she worked out really well and we kept her anyway (she was contract). It's just a nice courtesy and respect for you to tell them you are pregnant. Another thing is, you are saying you would come back part time after the baby is born? They need to know that expectation... in addition, do you even know if it's an option??? Proper etiquette is to tell them you are PG, be mature about it and cross your fingers that you'll get the job. :)

I want to commend you for looking for a job while pregnant. I think that working at a nursery sounds like a great job, but I also have some concerns. Is it smart to have a job where you're required to be in the summer heat ALL the time? Also, it's very physically demanding. You said that it is a small family business, so I'm going to assume that the benefits may not be the greatest. The owners may be apprehensive of taking on a pregnant employee for fear of driving up insurance costs.

I would dress however you feel the most comfortable. I wouldn't go to great lengths to hide my stomach, and I wouldn't flaunt it, either. I would volunteer the information after the interview has been conducted. I've never been to an interview where they haven't asked "Do you have any questions?" I think that would be the most opportune time to tell them. Be sure to tell them everything you've told us; that you're willing to work through the pregnancy and return shortly after delivery. Assure them that you feel physically prepared for the job and volunteer to have your doctor write you a note stating that you can lift things and spend long periods outdoors.

Good luck! I'll be thinking of you.

They may not hire you. If you can afford it I would wait until after I have the baby b/4 I go back to work.