Planting a Pomegranate: The Long Hot Autumn It Needs

Flowering is easy, ripening is not

Almost every disappointed pomegranate grower has the same tree: healthy, glossy, covered in scarlet flowers through midsummer, and still holding hard leathery fruit the size of a golf ball when the first frost arrives. Nothing is wrong with the plant. The flowers are free because pomegranate flowers on the current season's growth as soon as the wood is warm. Ripening is a separate job, and it takes far longer than most people expect.

From the day a flower is fertilized, a pomegranate needs roughly 120 to 180 frost-free days to fill, color and sweeten the fruit, and it needs those days to be genuinely hot and dry. The last six to eight weeks are the ones that count. If your autumn turns cool and wet while the fruit is still swelling, the sugars never arrive, the skin stays green or dull, and the arils inside are pale and sharp. The tree has not failed to fruit. It has failed to finish.

Before you buy soil or dig a hole, count backwards from your first frost. If you cannot find 150 warm days after midsummer flowering, plant the tree against your hottest wall or in a container you can move under cover, or accept it as an ornamental.

Fruiting forms and ornamental forms are not the same plant

A large share of pomegranates sold in general nurseries are ornamental selections grown for the flower, and many of them are double-flowered. A double flower has had its reproductive parts converted into extra petals. It is spectacular, it flowers for longer than a fruiting form, and it will never set a usable fruit no matter how hot your autumn is. If your tree flowers magnificently and drops every single flower without swelling, look at the flower itself before you look at the weather.

The difference is easy to see once you know it. A fruiting flower is single, with five to seven waxy petals and an obvious swollen base shaped like a small vase or bell sitting behind the petals. That swelling is the ovary and it is already fruit-shaped at bud stage. An ornamental double flower is a tight rosette of many petals like a small carnation, and behind it the stem is straight, with no vase. There are also dwarf forms sold as patio plants which do fruit, but the fruit is small, thin-fleshed and mostly decorative.

Site: heat, drainage, and shelter from autumn rain

Give a pomegranate the hottest, brightest, driest position you own. Eight hours of direct sun is a working minimum and ten is better. Reflected heat from a wall, a paved yard or a gravel bed is worth more than an extra hour of open sun, because it lifts night temperatures and night temperature is what drives sugar accumulation in the fruit.

Drainage matters more than fertility. Pomegranate tolerates poor, stony, alkaline and even mildly saline ground, and it tolerates drought once established, but it resents winter wet around the crown. On heavy clay, plant on a raised mound eight to twelve inches (20 to 30 cm) high rather than digging a deep pit that will hold water. A wall position has a second advantage that only shows in autumn: the overhang keeps some of the rain off the ripening fruit, and rain on ripening fruit is the single commonest cause of a split crop.

Getting the tree in the ground

Plant while the tree is dormant or barely moving, in late winter or early spring once hard frost has passed. Autumn planting works in genuinely mild areas but a young pomegranate sitting in cold wet soil all winter is the one situation that reliably kills them.

1. Dig wide, not deep Make the hole two to three times the width of the rootball and no deeper than the rootball itself. Planting deep is the most common early mistake, and a buried crown rots. The top of the rootball should finish level with the surrounding soil or half an inch (1 cm) proud.
2. Do not enrich the hole Backfill with the soil you dug out. At most add a tenth part of compost. Rich backfill produces a burst of soft leafy growth in the first two years and delays the first crop, and it keeps the root zone wetter than the plant wants.
3. Decide single trunk or multi-stem now A single trunk is tidier and easier to work under. A multi-stem bush of four to six trunks is more cold-hardy, because if one trunk is killed by a hard winter the others carry on. If you want multi-stem, let the basal suckers grow from the start and select the best five.
4. Space for the mature size Allow twelve to eighteen feet (3.5 to 5.5 m) between trees in the open, or eight feet (2.4 m) if you intend to keep them pruned as a fan on a wall. A crowded pomegranate shades its own fruiting wood and the inside of the bush goes bare.
5. Water in hard, then back off Soak the planting hole thoroughly once, then water deeply about once a week through the first summer only. From the second year, established trees need far less than you think.

Record the planting date, the position, and above all whether the first flowers you see are single or double. One line in your notes the first summer saves several years of wondering why a healthy tree never fruits.

Growing in a container where the season is short

A container is the honest answer for anyone whose autumn is too cool or too wet. Pomegranate takes to pots well, flowers young, and being movable means you can stand it in the hottest corner of the yard through summer and pull it under a porch, a carport or into an unheated greenhouse for the final ripening weeks, which is often all the difference you need.

Use a container of at least fifteen to twenty gallons (60 to 80 L) for a fruiting plant, with a gritty free-draining mix and no water-retaining additives. Feed lightly, water consistently rather than heavily, and expect to repot or root-prune every three to four years. Overwinter it dry and cool but frost-free; the plant is deciduous and wants a proper rest, not a warm windowsill.