It's hard to predict if the plant will grow well here for the long term since there are different pomegranate cultivars that have different degrees of cold tolerance. Maryland is borderline as far as winter temperatures go concerning pomegranate, either risking branch or entire-plant dieback if one year's weather is too harsh, or just risking not having enough time to ripen fruit. (An average of 6 months is needed frost-free, and central MD barely reaches that.)

With that said, it's still worth a try since you already have the plant. We have heard from pomegranate growers having success in some of the lower Chesapeake's Bay islands, plus southern Maryland, and while you are in Montgomery County and therefore slightly colder, you can still try using microclimate to your advantage. (More on that in a moment.) You could put the plant in the ground and try to shelter it from winter temperatures similar to how fig growers do (usually by wrapping branches with insulation to minimize wind and provide a few degrees of buffer from low temps, such as with an enclosure filled with fallen autumn leaves), since all you need is a small degree of cold protection. Or, you can grow it in a container that is brought into a cool but protected space in winter, such as an unheated garage or cool basement with windows for light. The goal in the latter case isn't to continue active growth on the plant during the dormant season, but instead to just allow any late-ripening fruit to become harvestable and to reduce the risk of winter damage to the branches while it waits to resume growth in spring.

A one-gallon pot is very small with regards to root insulation, so potting it into a larger container may be best if you try this approach. (We can't say how large, but would guess perhaps 12 inches in diameter, more or less. You could fill a container of the size above with soil to serve as insulation and then just pot the one-gallon plant with its pot still on for now, to make it easier to water while not over-watering.)

Microclimates are areas within a larger space (like portions of a yard) that have differences in growing conditions -- often in relation to warmer temperatures. This can result from structures that absorb, reflect, and/or retain warmth, such as house walls, retaining walls, solid fences, or pavement. They not only radiate heat from sun exposure during the day (which in summer won't bother the pomegranate) but can also boost overnight temperatures in the immediate area by a few degrees as that heat is released back into the air and surrounding soil. Placing plants with sensitivity to winter cold in such a spot, like in a sun-exposed corner of two walls or near a south-facing wall, is sometimes enough to carry them through the winter when they might otherwise be damaged elsewhere in the yard.

Bear in mind that pomegranate isn't a small shrub, so take into account eventual mature size if selecting a microclimate spot that's tight on space. The U.S. National Arboretum in D.C. used to have a well-established pomegranate that was roughly ten feet high and at least half that in width until it disappeared a few years ago; a cold snap it couldn't tolerate might have been the reason it was removed. (Outright cold doesn't always cause plant damage...instead it's sometimes the relatively rapid drop in temperatures from mild to below freezing in the course of a day or two where plants don't have enough time to adjust.)

Whether growing in a pot or in the ground, select a site that drains well and which receives full sun (6-8 or more hours of direct light daily in summer). Since you received the plant recently, it may have to stay indoors as a houseplant for now (especially if it was shipped from a warmer state) just in case it's not hardened-off enough to withstand the cold if planted now. If overwintered indoors, transplant it outside once we get closer to our frost-free date around early May. In the event it's kept like a houseplant, you can probably just leave it in that one-gallon container, periodically checking for watering needs, until spring planting since it won't outgrow that pot size that quickly.

Although UMD Extension has little information on cultivating pomegranate since they are so rarely grown here, there are a few web resources that might be useful if you search, including a ~140-page book called The Incredible Pomegranate. (It used to be available virtually online from the Univ. of California, though now only seems to be available in print from various sellers.) We have read that plants will need to be at least two or three years old before they can start bearing fruit, and since they're self-pollinating, you won't need to worry about a pollinator. Fruits don't ripen once picked, so try to make sure that late-ripening fruits are ready to harvest before picking them. (That is, you can't pick them early like you can with tomatoes.)

Long-term, the plant might sucker (grow new shoots from the root system) if it's growing well, so you may want to keep their number to about a half-dozen or so that become its main stems, removing others as they appear to direct the plant's resources into those main growth points. If branches die back drastically after a winter, give the plant time in spring before writing it off as totally dead, since if the roots survived, the plant can regenerate new branches. (In that case you probably would not get fruit again for a couple of years.)

Clay-based soil is probably okay as long as it drains well. Mixing-in organic matter (compost) can help keep clay soils from compacting too much and starving roots of oxygen. Avoid adding sand to clay for the purposes of improving drainage; it doesn't work well unless very large volumes are added, which would not be practical. If you have concerns about drainage, consider growing the shrub in a raised bed, the same way vegetables and herbs are often grown (though perhaps a bit deeper of a bed, so the shrub roots have more room in that well-drained setting).

Miri