I have really mixed feelings about Merrifield. I've been quite a few times and I'm constantly impressed with the knowledge and helpfulness of the outdoors staff. I once brought in a crappy plant photo on my dad's old flip phone and two of them worked together to identify what it was. They are great at recommending native and deer-resistant plants and have a great selection (they even have monkey puzzle trees! I want, but they are $$$). If Merrifield were only the outdoor staff, they would get 5 stars, easily. These guys are great and the plants always look healthy.
Then you walk inside. My biggest complaint is with the greenhouse, but before I get there, I'll say that the staff inside (but in not the greenhouse) seem apathetic and have been generally unhelpful. Not terrible, but definitely don't know enough to answer even basic questions (or they just don't feel like figuring it out--hard to tell). Also, basic stuff (such all ground covers and all the miracle gro brand stuff) can usually be bought half a mile away at Home Depot for literally half the price.
Now for the greenhouse! The six or so times I've been, there has always been the same lady in the greenhouse, and she is impressively unfriendly, unhelpful, and unknowledgeable (triple whammy!). I have a ton of carnivorous plants, succulents, and cacti, so I know some stuff about them. Almost all the succulents and cacti are just labeled "succulent/cacti" + the pot size and the lady wasn't able to identify the species or even the genus when I overheard someone else asking about them. Also, the selection is not that great and a lot of the succulents, cacti, and carnivorous plants are in pretty bad shape. The succulents are clearly overwatered--several were rotted (and definitely not going to recover) but still out for purchase...I guess because the very tops look okay, so someone who knows nothing might still buy it? I pointed it out to the lady who works in the greenhouse and she declared that 'succulents just do that sometimes, it'll be fine' which is completely false. If you have ever owned a succulent and have overwatered it to the extent that its root system has rotted away, the succulent is dead. The only thing you can do is take cuttings from non-rotted areas and hope they re-establish (but that's easier on larger plants, whereas these are little plants that I see rotting at Merrifield). If you are careful in your selection, and don't mind overpaying, you can find some decent succulents of the most common varieties. The little starter pots are $3.99 a piece, the slightly larger ones are $7.99 and $12.99, and then they quickly get more expensive. I have bought succulents here because there aren't many garden centers in the DC area, but I'm always taken aback by how expensive they are. Also, watch for pests! I've noticed problems with some.
The greenhouse has two different types of pitcher plants (both Nepenthes, N. ventrata and N. miranda) and they are always so sad looking, with almost all their pitchers shriveled (they only had two N. miranda last time I was there, and one had all its pitchers at least half shriveled and the other plant had one glorious, happy pitcher, and the rest were all shriveled). Home Depot down the road, much to my surprise, actually has the same two species of Nepenthes and they were in much better condition. The N. miranda at Merrifield cost $59.99 (or maybe it was $56.99) and the N. miranda at Home Depot--which was perhaps slightly smaller but had many more healthy pitchers--was $24.99. The N. ventrata at Merrifield was ~$20 ($19 and change, I think) and was ~$17 and change at Home Depot. The N. ventratas were from the same supplier, too. Couldn't check about the N. mirandas, because the ones at Merrifield were hanging too high up for me to look at the tag.
And one last note on the lady who works in the greenhouse--once I was carrying a ton of plants in a basket and she smacked me (by mistake) with the hose (on her way to over water the poor succulents, I imagine) and tripped me. I spilled a ton of plants out of my basket as I fell (and they sell their succulents with the most obnoxious coarse sand/tiny rock ground cover, so it escapes spectacularly when you fall...also, it holds water well, which isn't great for cacti and succulents). The greenhouse lady looked at me as I struggled to get my plants back upright in the basket and then walked away. That's next level unfriendly!
Edited to add that plants in the greenhouse that do have species labels are often incorrect, so if you are worried about toxicity or want a specific species, google to double check.
