Garden Q&A: How to experiment with growing pomegranates in Maryland

Q: Will pomegranate grow in Maryland? I imagine not, but it would be fun to add to my fruit garden if I can get away with it.

A: Pomegranate (Punica granatum) is a large-growing shrub or small tree that’s rated cold-hardy to USDA zone 8 and above, with the most stalwart selections rated to zone 7, so that would make it borderline hardy overall in Maryland. Even so, D.C. and southern Maryland, plus some of the lower Chesapeake islands, can have success for at least a handful of years at a time before the chances of a harsh cold snap risks causing drastic damage or plant death. The heat-island effect in Baltimore City might similarly make it just insulated enough to be worth a try. Look for cultivars with origins in central Asia, as these tend to be the most cold-hardy.

Depending on temperatures, some years the plants may survive just fine but fail to fruit. I have read that high humidity during flowering (uh-oh) can also result in poor fruiting. Their intensely vibrant orange-red summer flowers that have the petal fullness of a carnation are reason enough to include a plant, though, especially if you have a hot color scheme in the garden or like using species that give a bit of a tropical vibe.

Pomegranate blooms so late in the growing season compared to common fruits that we cut it pretty close when it comes to having enough time for ripening. (They take an average of six months after pollination, or about 180 frost-free days. Maryland ranges from 150 to 225, depending on location.) Some cultivars ripen slightly faster than others, so those would be more suited to cultivation in our area so they can hopefully be harvested just before we start to freeze. Fruits don’t ripen once picked, alas, so you can’t rescue the nearly ready like you can tomatoes at the end of the season.

You can try using microclimate to your advantage, though, by placing plants near sources of reflected and retained heat, such as by a wall, stone pile, or pavement (as long as the rest of the root system has enough good soil). Fortunately, fruits reportedly are at their best when developing in periods of high heat, and the warmth radiating from such surfaces might boost its winter survival odds as well. (All you may need is a few degrees.)

While other insufficiently-hardy fruits can be overwintered indoors, like citrus, pomegranate reportedly does not do well when brought inside as a houseplant. If you wanted to experiment, a cool greenhouse would better meet their needs than under grow lights (or, worse, with no supplemental light) indoors. If you’re not concerned with active growth or leaf retention, perhaps a potted specimen could spend the winter in a sheltered, unheated garage to take the edge off the worst of the cold. You could also see if wrapping an in-ground plant for the winter, as gardeners do with figs, is successful.

Q: Last year I learned I had that new-ish pest fly (forget the name) damaging my garlic. How do I keep it from coming back this year?

A: You’re probably thinking about allium leafminer (ALM), a pest from Europe first recorded in our region back in 2015. The larvae of this fly bore into leaves first — the leafminer part of their name — later moving down the stem into the bulb, which is the more damaging aspect of their behavior. The other part of their name comes, predictably, from their host plant of choice, Allium, the genus to which edible and ornamental onions, leeks, garlic, shallots, chives, and scallions belong.

It may seem premature, but late February to early March is the time to get overwintered Allium crops protected in central Maryland. A floating row cover or fine-mesh insect netting (or a comparable fabric like the tulle you may have used for 2021′s cicada bonanza) should effectively exclude the adults. Since the first generation of adult flies emerges in March/April, having a crop covering already in place should prevent egg-laying and the resulting damage to your plants later in spring.

These spring adults arise from pupae that overwintered in plant debris or in soil, so use caution if covering a bed you know had problems with ALM last autumn, since you don’t want to trap the pest inside with free access to an all-you-can-eat buffet with protection from predators to boot. Alternatively, you can try to knock down the population by lightly cultivating the soil around the plants to bury pupae so they won’t hatch or to expose them to predators or harsh weather. If ALM remains a problem, try to rotate to another crop after the harvest so this pest doesn’t have a ready food supply.

Once that first generation pupates, they sit around and wait out the heat, maturing into adults in early autumn. Since each of the two adult generations can be flying for a window of time almost two months long, keep those covers in place as a first line of defense against infestation. As a last resort you can try an insecticide; visit our Allium Leafminer page for more life cycle details and recommendations for organic pesticide options and their timing of use.

University of Maryland Extension’s Home and Garden Information Center offers free gardening and pest information at extension.umd.edu/hgic. Click “Ask Extension” to send questions and photos.