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An established mulberry is deep-rooted and drought-tolerant, and in most seasons you will never water it. The exception is the stretch from fruit set to the start of ripening. A dry spell in that window makes the tree shed part of the crop while it is still green and hard, and shrinks what is left. Watering after the fruit has begun to color does the opposite: it dilutes the flavor and can split the berries.
So the rule is simple. From the time small green fruit is visible until the first berries start turning red, keep the root zone evenly moist, giving a deep soak of fifteen to twenty gallons (60 to 80 L) every week or ten days if there has been no meaningful rain. Once coloring starts, stop, and let the tree finish the crop on what is in the soil.
| Stage | Watering | Why |
|---|---|---|
| Bud break to flowering | Only in prolonged drought | Roots are still in cool moist soil |
| Fruit set to first color | Deep soak weekly if dry | Prevents green fruit drop and small berries |
| Coloring and picking | Stop watering | Water now dilutes flavor and splits fruit |
| After the crop, late summer | Water in severe drought only | Keeps leaves working without forcing soft growth |
| Dormant season | None | Wet roots in cold soil cause more harm than dry |
Feeding: less than you think
Mulberries grow fast without help. Feeding a tree that is already making three feet (90 cm) of extension in a season produces soft, over-long shoots, more leaf shading the fruit, and wood that is slower to harden before winter. A tree in reasonable soil under a mulch of compost needs no fertilizer at all.
Feed only when the tree tells you to. Shoot extension under about eight inches (20 cm) on a young tree, small pale leaves, or a crop that stays undersized two years running are the signals. In those cases spread a balanced granular feed over the root zone in early spring at the rate on the packet, or two to three inches (5 to 8 cm) of well-rotted compost out to the drip line, and then leave it alone for another year. Never feed after midsummer.
Lawn feed drifting onto the root zone is a common accidental cause of rank, unfruitful growth on a mulberry planted in grass. If the tree stands in a lawn you feed, keep a mulched circle around it and steer the spreader away.
Mulch, grass and the surface roots
Mulberry roots run wide and shallow. That is useful, because a surface mulch reaches them directly, and it is a nuisance, because digging or rotavating under the canopy tears roots and provokes suckers. Keep the ground under the tree undisturbed. Renew a two to three inch (5 to 8 cm) mulch of compost, leaf mold or bark each spring, spreading it out to the drip line and leaving a gap around the trunk.
Grass growing right to the trunk competes for water at exactly the depth the tree uses, and the mower is the single most common cause of trunk damage on young mulberries. A mulched circle three feet (90 cm) across solves both problems.
Keeping the size honest
A mulberry left entirely alone becomes a wide, low, heavy-limbed tree, and on an old specimen the outer branches sag until they touch the ground. That is a fine thing in an orchard and a problem in a garden. The way to hold size is little and often over years, not a rescue operation once the tree is enormous. Details of when and how to cut are covered in the pruning guide; the principle for day-to-day care is to shorten anything heading somewhere you do not want it while the shoot is still thumb-thick.
Prop or shorten heavy horizontal limbs before they crack. Mulberry wood is brittle for its weight, and a limb carrying a full crop and a night of rain will split at the union sooner than you expect. Any branch lower than head height across a path will end up dropping staining fruit on people walking under it.
Containers and trees against a wall
A mulberry in a large container stays small enough to move out of the way during the messy weeks, which is the main reason to grow one this way. Use the biggest pot you can shift, twenty gallons (80 L) or more, in a soil-based mix rather than a peat or coir compost, because the tree will live in it for years and the extra weight keeps it upright. A container tree cannot forage, so it needs watering thoroughly through the whole growing season, daily in hot weather, and a balanced liquid feed every two to three weeks from bud break until the fruit starts coloring.
Repot or root-prune every two or three years in the dormant season: slide the tree out, cut an inch or two (3 to 5 cm) off the outside of the root ball all round, and return it with fresh mix. Wall-trained trees are treated the same as any restricted fruit tree, with the framework tied in and side shoots shortened in late summer.
The record that pays off
Keep one line per year for each tree. Write the date of bud break, the date the first fruit colored, whether you had to water and how many times, and roughly what the crop was like. After three or four seasons the pattern is unmistakable: you will know how many weeks after bud break to expect the first pick, whether your soil actually needs the watering you have been doing, and whether the years you fed produced any more fruit than the years you did not. Most gardeners discover from their own notes that the feeding made no difference at all.