How to Grow and Care for the Pumpkin Ash

When most people think about pumpkins, they think orange, cool weather, and the ever present "spice," but none of those things have anything to do with the pumpkin ash. It doesn't have orange leaves, doesn't like particularly cool weather, and has absolutely nothing to do with fall spices.

The pumpkin ash is a rare tree that, like other native trees in the genus Fraxinus, has become even more rare in recent years due to the emerald ash borer. It is most commonly found in wet swampy areas, with a habit of growing in deep standing water. The botanical name Fraxinus profunda, or "Deep Seated Ash" comes from this trait. The pumpkin ash can be recognized by the seven to nine leaflets which are often the same color as the white ash on the top, but are a light green with a fine hair on the underside. "Pumpkin" in the common name comes from the swollen appearance of the buttresses or "knees" at the base of its trunk.

Pumpkin Ash Care

If you come across this tree in your landscape, it's more than likely that the tree has naturally grown there, as it is not often available in the nursery trade. One of the rare occasions that the pumpkin ash is desired in a garden setting is in a rain garden, where, if properly maintained and cared for, it can be an intriguing option as the garden’s centerpiece. Even so, due to the tree's issues with the emerald ash borer and other diseases, there are much more desirable options available on the market.

Soil

The pumpkin ash prefers wet, loamy soils. It is very susceptible to drought damage and should have consistently moist soil. The "knees" develop from growing in areas that remain wet throughout the growing season, and provide extra stability for the tree. These buttresses are less prominent in dryer soils.

Water

Water the pumpkin ash often during dry seasons or drought. It is easy to under water but hard to over water this tree.

Light

The pumpkin ash prefers full sun.

Fertilizer

The mature pumpkin ash does not typically need feeding.

Pruning

The basics of pruning are the same on any tree in the genus Fraxinus. Prune to establish a single leader, or main trunk, as you would with any tree with opposing branch structure like the pumpkin ash. Wait to begin pruning for two to three years after planting. This structural pruning is an on-going process that needs to happen yearly while the tree is young. Always try to prune in mid to late winter when the tree is dormant and has the best chance to heal by developing new growth in the spring.

As the tree matures, you will want to prune to remove dead, dying, damaged, or diseased branches, so issues aren't spread to healthy parts of the tree. Pruning also allows for the perfect opportunity for a closer inspection of your tree to find any issues that might not be so clear from afar.

When pruning an ash, always remember to check if you are under quarantine before you dispose of any waste. You can call your local DEP or extension agency for clarification.

Emerald Ash Borer

As with all native ash, the most prevalent threat since 2002 is the invasive emerald ash borer. The borer is currently devastating the ash populations in much of the United States and it is expected to eventually spread to all corners of the country and north into Canada, to a range where cold mitigates the pest's spread. With this in mind, the assumption is that your ash tree will be infested.

Fortunately, borer infestations can be fought with some close inspection and effort. Knowing the signs and symptoms that your tree has become infested is the most important weapon in your arsenal in fighting these terrible insects. Watch for canopy thinning and crown dieback, random leafy growth from stress, woodpecker damage, D-shaped exit holes, S-shaped galleries or grooves, and splitting bark.

When any of these are present, look to see if there are other signs and symptoms of a borer infestation. If there are, you may want to consider the three options available to you: treating it yourself with pesticides, hiring a certified arborist who is also a licensed pesticide applicator, or if more than one third of the tree is damaged, removing the dying tree.

Ash Yellows

Ash yellows is another cause for the decline in ash populations in North America. Unlike a borer infestation, yellows has no known cure. The disease is caused by a virus that affects the vascular system of a tree and leads to its eventual death. The symptoms to look for are slow twig growth and rapid die back. In 2016, a discovery of mature pumpkin ash trees in Central Park led experts to believe it may be somewhat resistant to the disease.