Planting an Avocado Tree: Grafted Plants, Pit-Grown Seedlings and Drainage

A tree from a stone is a houseplant, not an orchard

Sprouting a stone on a jar of water is how most people meet this plant, and it is worth being blunt about what you have. A seedling avocado takes somewhere between five and fifteen years to reach flowering size, and a great many never fruit at all in a garden. When one does, the fruit is a genetic lottery: the seed came from a cross, so the tree will not repeat the fruit you ate.

The other problem is size. A seedling grows straight up on a single dominant leader and wants to be a forest tree, sixty feet (18 m) and more where it is warm enough. It also holds its juvenile habit for years, and juvenile wood does not flower. None of this is a reason to throw the seedling out, but treat it as a foliage plant and a rootstock experiment rather than a source of fruit.

If you want fruit within your own attention span, buy a grafted tree. A graft carries mature wood from a tree that already fruits, so it flowers on schedule regardless of how young the root system is: expect the first small crop two to four years after planting. The graft union is the swollen, often kinked joint a few inches above the soil, and everything above it is what fruits.

If you already have a seedling you are fond of, you can graft mature wood onto it once the trunk is about half an inch (1.2 cm) thick. That converts the years you have already spent into a tree that can flower.

Drainage kills more avocados than cold does

Avocado roots are shallow, fleshy and unusually poor at tolerating low oxygen. Standing water for as little as two or three days in warm soil is enough to start root death, and the fungal root rots that follow are effectively untreatable in a garden. Before you think about anything else, work out where the water goes after heavy rain.

Dig a hole a foot (30 cm) deep where you intend to plant, fill it with water, let it drain, then fill it again. If the second fill has not gone in eight hours, that spot is not suitable for planting at grade. Plant on a mound instead, or use a container. Raising the root zone is not a refinement; on heavy ground it is the difference between a tree and a dead stick.

1. Build the mound before you dig On clay or any slow-draining site, heap native soil into a mound twelve to eighteen inches (30-45 cm) high and three to four feet (90-120 cm) across, then plant into the top of it. The roots stay above the waterlogged layer all winter.
2. Dig only as wide as you need, and no deeper Make the hole the same depth as the rootball and about twice as wide. A deeper hole backfilled with loose soil lets the tree settle, and a sunken trunk base is the classic route to collar rot.
3. Do not enrich the backfill Backfill with the soil you took out. Filling the hole with compost or potting mix creates a sump that holds water against the roots and discourages roots from leaving the hole. Put the organic matter on top as mulch instead.
4. Set the rootball an inch proud Plant so the top of the rootball sits about an inch (2-3 cm) above the surrounding soil, and taper soil up to it. The graft union must stay well clear of the soil and of any mulch you add later.
5. Tease nothing, cut only circling roots Avocado roots snap and resent handling. Slide the rootball out intact and only slice through roots that circle the pot. Aggressive root washing or teasing sets the tree back a whole season.
6. Water in slowly, then leave it alone Give five to ten gallons (20-40 liters) slowly at planting so the rootball and the native soil knit together. After that, water only when the top two inches (5 cm) of soil have dried.

Spacing, shelter and the first summer

Give a grafted tree at least fifteen to twenty feet (4.5-6 m) from walls, fences and other trees, and more if you do not intend to prune. Crowded avocados shed their lower branches, and fruit then sets only where you cannot reach it. In a small garden, plan on keeping the tree to twelve or fourteen feet (3.5-4 m) by annual pruning and space it accordingly.

Young bark burns. A newly planted tree has thin, green-tinged bark and very little canopy to shade it, and a hot, exposed trunk cooks on the sunny side. Paint the trunk and the main limbs with white water-based paint thinned by half with water, or wrap them loosely with light cloth, for the first two summers. This looks fussy and it prevents a very common early loss.

Wind is the other early enemy. The leaves are large and the wood is brittle, and a windy site produces torn foliage, scarred fruit and snapped limbs. A temporary windbreak on the prevailing side for the first two years pays for itself; a permanent one on an exposed site is not optional.

Growing in a container

A container is the honest answer wherever winters drop much below freezing, and it also solves bad drainage. Use a grafted tree on a dwarfing rootstock if you can find one, and accept that the crop will be small: a few dozen fruit at best from a well-run tub, not a bushel.

Pot up in stages rather than starting in the final container. Oversized pots stay wet in the middle, and wet is the one thing this plant will not forgive. Use a coarse, free-draining mix built on bark and pumice or perlite rather than a peat-heavy potting mix, and choose a pot with generous drainage holes that never sits in a saucer of water.

Write down what you planted, the date it went in the ground, whether it is grafted, and which flowering type it is. Three years on, when you are trying to work out why fruit set is poor, you will not remember any of it.