Gadenin日本語Get the appYoung pawpaws scorch in the sun that a mature tree needs
Asimina triloba grows wild as an understory tree, coming up in the filtered light beneath larger hardwoods and only reaching full sun once it has height. That history is written into the seedling. A pawpaw in its first two years carries a light-sensitive leaf that bleaches, browns at the margins and drops if it is planted straight out into open ground, and a tree that defoliates in its first summer may not come back at all.
The adult tree wants the opposite. A pawpaw grown permanently in shade makes a thin, leggy trunk, flowers sparsely and ripens small fruit with poor flavor. Full sun is what fills the canopy and sweetens the crop. So the site you choose has to be a sunny one, and the shade has to be something temporary that you put over the tree and then take away.
The practical answer is 50 percent shade cloth on a simple frame, or a tripod of stakes with burlap on the south and west sides, left in place for the first two growing seasons and removed at the start of the third. Do not plant permanently under a mature tree instead: the root competition and the deep shade both hold the pawpaw back, and you cannot remove a tree canopy the way you can remove a screen.
Watch the leaves rather than the calendar. If new growth in the second summer stays deep green and unbleached at the edges by midday, the tree is ready to come out from under the cloth.
Ground, drainage and pH
Pawpaw is a bottomland tree. In the wild it grows on deep, fertile river-terrace soil that stays moist all summer and never sits waterlogged in winter. Reproduce that and the tree needs very little else. Aim for a slightly acid soil, pH 5.5 to 7.0, with real depth to it, and enrich a wide area with leaf mold or well-rotted compost worked into the top eight inches (20 cm) rather than dumping it in the hole.
The failure to avoid is standing water. Pawpaw tolerates a flood that drains away, but roots left in saturated soil through a cold winter rot. Dig a hole a foot (30 cm) deep and fill it with water; if it has not drained inside twelve hours, plant on a raised mound at least eighteen inches (45 cm) high. Equally, do not plant on a dry, shallow, stony bank. A pawpaw that dries out repeatedly in its first summers stalls for years.
Give the site shelter from wind. The large leaves, up to a foot (30 cm) long, tear and desiccate in an exposed position, and a windy site also empties of the small flies and beetles that carry the pollen.
| Site factor | What pawpaw wants | What goes wrong if you ignore it |
|---|---|---|
| Light, years 1-2 | Roughly 50 percent shade | Leaves bleach and scorch, tree defoliates |
| Light, year 3 onward | Full sun, 6+ hours | Thin growth, few flowers, small bland fruit |
| Soil pH | 5.5-7.0 | Yellowing between the veins on limy ground |
| Drainage | Moist but free-draining | Winter root rot in saturated soil |
| Wind | Sheltered | Torn leaves, poor insect visits at flowering |
| Spacing | 15-25 ft (4.5-7.6 m) apart | Crossing canopies, fruit only in the tops |
You need two genetically different trees
A pawpaw flower will not set fruit from its own pollen, and neither will a flower pollinated from anywhere else on the same tree. The tree is self-incompatible, so one specimen on its own flowers heavily every spring and drops every flower. Suckers pulled off one parent are that same tree genetically, and a row of them will never crop. Two trees raised from different seed parents, or two different grafted selections, are what you need.
Because the pollen is carried by flies and beetles, not by wind or foraging bees, it does not travel far. Plant the pair within 30 feet (9 m) of each other and closer is better. Two trees 100 feet (30 m) apart at opposite ends of a garden will set almost nothing even though both flower well. If space is tight, plant two trees in one wide hole three feet (90 cm) apart and grow them as a twin-stemmed tree.
Getting the tree into the ground without breaking the taproot
Pawpaw makes a long, brittle, sparsely branched taproot with very few fine feeder roots, and it does not regenerate them quickly. That single fact governs how the tree is planted. Bare-root pawpaws transplant badly and often die outright; buy a tree in a deep container, a tall tree pot or root-pruning pot rather than a wide shallow one, and plant it in spring as the buds begin to move rather than in autumn.
- Plant in spring, not autumn Wait until the soil has warmed and the buds are swelling. Pawpaw roots grow only when the soil is warm, so an autumn planting sits inert through winter with a damaged root system and no way to repair it. Spring planting gives the tree a full warm season to re-root.
- Dig deep rather than wide This is the opposite of the usual advice, and it is because of the taproot. Make the hole deep enough that the taproot hangs straight down without curling or being folded back on itself. A coiled taproot strangles the tree over the following few years.
- Slide the rootball out intact Do not tease out, wash or cut the roots. Cut the pot away if you have to. Any handling that shakes soil off the taproot costs the tree a season. Set it at the same depth it grew in the pot and firm gently, then water in with several gallons to close air pockets.
- Mulch, then shade Put down three inches (7.5 cm) of wood chip or leaf mold over the root zone, kept an inch (2.5 cm) clear of the trunk. Then set up the shade screen before the first hot, bright day, not after the leaves have already burned.
- Record what you planted and where Write down which tree came from which source and its position in the garden. When you start hand pollinating you will be moving pollen between specific trees, and knowing which two are genetically different is the difference between a crop and an empty year.
If you are starting from seed
Pawpaw seed is recalcitrant: it dies if it dries out, and it dies quickly. Seed cleaned of pulp and left on a windowsill for a few days is dead seed, and it looks exactly the same as live seed. Clean the pulp off, keep the seed damp from that moment onward, and never let it reach the point where the surface goes dull and papery.
Store the damp seed in a bag of moist sphagnum or barely damp sand in the refrigerator at about 40F (4C) for 90 to 120 days, then sow it an inch (2.5 cm) deep in a deep pot in warm soil, 75F (24C) or above. Germination is slow and hidden: the root goes down for several weeks before any shoot appears, so a pot that looks empty for two months is normal. Seedlings take five to eight years to fruit and will not be identical to the parent.
Never freeze pawpaw seed and never dry it for storage. Refrigerated in damp medium it keeps for a couple of years; dried on a bench it is dead within a week.