Thornless honeylocust

About Thornless honeylocust

Thornless honeylocust is the thornless form of a native tree. Its tiny leaflets cast light, dappled shade, so lawn grass grows underneath, and they nearly vanish when they fall. Named cultivars are thornless and mostly seedless; the wild tree has big three-forked thorns and long, messy pods and can spread in pastures.

Zones 3-8 (NC State). The wild, thorny form can turn weedy in pastures (NC State).

When to plant

Timing is counted from your average last spring frost (and first fall frost). Sow & Tell works out the actual dates for your ZIP code.

Plant container or balled-and-burlapped trees. Container trees can go in any time the ground can be worked, but fall is the best season in the South because roots keep growing through mild weather (Clemson). Dig the hole no deeper than the root ball and at least twice as wide, keep the top roots level with the soil, and mulch 2-4 inches without touching the trunk. Mowing or cutting roots makes it sprout (NC State).

Soil

Adapts to clay or loam and acidic to alkaline soil, and tolerates drought, salt, wind and pollution; best in moist, well-drained soil (NC State).

Test the soil first. Loosen a wide planting area and mix 10-20 percent compost into the native soil you dig out; don't use uncomposted bark, and don't dig deeper than the root ball (Clemson).

Feeding

• Spring to early summer, after the tree is established, and only if a soil test or pale leaves and weak twig growth show a need: slow-release nitrogen fertilizer with a ratio near 3-1-1 or 3-1-2 (3-0-1 or 3-0-2 if the soil test shows enough phosphorus). Spread it evenly from just outside the trunk flare to the dripline and water it in. Clemson cites 2-4 lb of slow-release nitrogen per 1,000 sq ft per year, split into a spring and a late-summer feeding; follow your soil test.

First-year watering matters far more than fertilizer: water daily for the first 1-2 weeks, every 2-3 days until week 12, then weekly, using about 1-1.5 gallons per inch of trunk diameter, until the tree is established, roughly 1.5 years per inch of trunk (UMN). Don't count on rain unless it was over an inch. Avoid wounding roots and trunk; mowing and cutting make it sprout (NC State). Too much fertilizer can burn roots and push soft growth that pests and cold injure (Clemson).

Harvest

Small, sweet-scented flowers hang in clusters in late spring for about two weeks; no deadheading needed. Wild trees set 12-18 inch twisted pods that turn black and drop over winter (NC State).

Varieties (4)

NC State documents 4 thornless cultivars, all from var. inermis.

Pests to watch for

Fall webworm, Leafminers, Eriophyid mites (rust, bud, blister and gall mites), Annual cicadas (dog-day cicadas), Cankerworms (fall and spring cankerworms)

Diseases and problems

Leaf spot, Canker, Powdery mildew, Rust, Mechanical damage (mower, trimmer and tie wounds), Girdling roots

In the kitchen

The sweet pulp inside wild-type pods is edible raw or cooked, though wildlife and livestock eat most of it (NC State).

Pets: NC State tags honeylocust as non-toxic to cats, dogs and horses. The 'Locust' on the ASPCA's toxic list is black locust (Robinia), a different tree.