Matching feeding to actual growth

April in the courtyard. Like every case in this course, it is an instructional example, set in one temperate Northern Hemisphere city at about 40° N (USDA zone 7a). The courtyard maple, the healthy, established trident maple (Acer buergerianum) whose mix Course 04 documented (Course 04, Lesson 6), is leafing out in its moderate-depth terracotta training pot of akadama, pumice, and lava. It gets morning sun and afternoon shade, and its owner checks it morning and evening. A long low branch has been left to grow freely to thicken the trunk below it. This is a tree in development, and its owner wants a feeding plan they can write down and keep to.

On the courtyard's display bench stands the owner's older trident, in a shallow glazed pot. Years of pruning have given it fine twigs and small leaves, and the owner wants to keep them that way. Both trees will be fed from one bottle of the 8-4-6 liquid fertilizer. Its label, read line by line in Lesson 2, is a fictional label made for this course, as every label in the course is. Should the two trees get the same plan?

On the west balcony, the trident maple was repotted in early March, with a club member's help, into a coarse mix of akadama, pumice, and lava, after its roots had matted over the drainage holes (Course 03, Lesson 7). A month on, its buds have opened and small leaves have unfolded, but no shoot has begun to extend. It has never been fed, and its owner wonders whether a first feed now would help it recover.

Both owners face the question every feeding plan has to answer: how much, and how often, for this tree now? This lesson builds a starting plan from the label for the courtyard maple, then shows how to read the growth, and how the season, the goal of development or refinement, the roots, and the weather change when and how much a tree can use.

A starting plan from the label

Course 01 set the starting point: feed a healthy, actively growing tree at the rate and interval on its fertilizer's label, and note each feeding (Course 01, Lesson 10). The label is the place to start because its maker has set a rate for each use, and no course can give one rate for every product: a can's strength depends on the product and on the directions line you choose (Lesson 2). A plan writes that line down with the tree, its conditions, and what would make you change course.

The courtyard maple's plan

The owner already keeps a batch record for the mix and a watering log. In April, before the first feed, they add the plan:

Each line has a reason. The tree and its conditions are the plan's assumptions: the same product and line could be wrong for a tree just repotted, resting for winter, or kept compact. The mix of akadama, pumice, and lava holds few nutrients of its own, and every thorough watering carries some out, nitrate most readily, so a growing tree in it depends on regular feeding (Lesson 1). The water matters because the 8-4-6 lists no calcium: the city's tap water supplies some calcium and magnesium, while a tree on rainwater alone would need a feed whose label lists both (Lesson 2).

The start, taper, and stop are stages of growth, not dates; the sections below explain each. Feeding a moist mix follows the label's own direction, “Water dry potting mix with plain water first, then apply to the moist mix until a little runs from the drainage holes.” Lesson 6 sets out the line for the feeding record and puts the plan on one card.

On each feeding day, check the tree first, as you would before a watering (Course 03, Lesson 2), then make one of three decisions. Feed as planned means feeding today at the plan's rate. Not now: hold the feed defers it for a reason the plan names. Investigate before feeding is for poor growth or color with a cause you have not checked, such as the roots, the water, the light, salts, or pH: it means checking those first, never feeding by default (Lesson 5).

Weaker, more often

Some bonsai growers split the label's feed into smaller, more frequent ones: for the courtyard maple, half strength, 4 mL in the 2 L can, every 7 days instead of the outdoor line every 14. Over each fortnight the tree gets about the same, so this is one label-consistent way to deliver a similar total, and in a free-draining mix it keeps the supply a little steadier between feeds, at the cost of twice as many feeding days to remember and record. It is a routine, not a gentler kind of feeding: no help to a tree that has just arrived, no cure for weak growth, and no way to feed roots that are not working yet.

Read the growth before you change the plan

A plan is a starting point, and the tree's growth is the evidence of whether it suits. Before you change the amount, the interval, or the product, read what the tree has grown since the last change, against what it usually grows at this stage.

What to look at

Five things are worth a look at every check, and a closer one every week or two:

• Shoot extension. Are new shoots lengthening at this tree's normal pace, and how long are the bare stretches of stem between one leaf, or pair of leaves, and the next? Those stretches are internodes: fast, free growth makes them long, and slower growth in strong light makes them short (Course 01, Lesson 5).
• Leaf size. New leaves at full size for the tree and their place on it, or smaller than the ones before, or larger.
• Leaf color, newest and older. Note whether any paling starts on the older leaves at the base of this year's shoots or on the newest. Because of nutrient mobility, where it starts is a clue to what may be short, not a verdict (Lesson 1).
• Buds and hardening. Later in the season, plump buds forming at the leaf joints and tips, and shoots firming from the base.
• Roots at the holes. New white root tips at the drainage holes or under the rim show roots that are growing. Seeing none is an unknown, not a bad sign.

Judge each against what this kind of tree usually does at this stage, which is what Course 01 calls vigor (Course 01, Lesson 14). In mid-spring a healthy trident can add several pairs of leaves per shoot within a few weeks, while a healthy juniper shows only modest, paler green tips, and feeding a juniper more will not make it grow like a maple. Compare this year with last year too: the bud scale scars at the base of each shoot mark where the season's growth began, and the weekly photo from the same spot that the watering log asks for shows changes too slow to see day to day (Course 03, Lesson 7).

How long a change takes to show

A feed changes the leaves and shoots that form after it, not those already grown: a leaf that expanded small stays small, and one that came out pale may stay pale. So judge a change by the next new growth over the following weeks, against comparable weather and the same stage of the season, and change one thing at a time. If you change the feed in the week the tree moves into more light, the log cannot say which made the difference (Course 03, Lesson 7).

Each row sends you to look somewhere, not to a verdict.

Growth phases change what a tree can use

A growing tree uses mineral nutrients as it builds leaves, shoots, roots, and wood, so what it can use from a feed rises and falls with its growth. A temperate tree's growth starts, peaks, slows, and stops through the year; an indoor tropical tree's follows its light and warmth. The plan's interval belongs to the growing part of the year.

Spring: start once the flush is growing

At bud break a trident has no working leaves, and its first flush runs largely on reserves stored the year before (Course 01, Lesson 9). Its roots are only waking in the cool mix, and cold roots absorb slowly (Course 01, Lesson 10). A feed poured as the buds swell mostly waits in the pot while waterings wash it through, and fertilizer cannot power the buds themselves. Until growth is under way, the decision is Not now: hold the feed until growth starts.

The first feed goes on once the flush is growing: shoots extending, new leaves expanding, and roots active again in a warming pot. For the courtyard maple that usually comes in late April in the example city, though the date moves with each spring. Feeding then mostly supports the growth that follows, as the flush's own leaves take over from the reserves, and from then on the plan runs at the label's rate and interval for as long as the tree keeps growing. No calendar date can stand in for that check: the same day in April can find one trident in full flush and another, freshly repotted, not yet growing.

Late summer and autumn: taper, then stop

In late summer a trident's shoots stop extending and form next year's buds, and the soft new shoots firm and turn woody, which growers call hardening (Course 01, Lesson 13). That bud set is the signal to taper: feed lighter or less often, such as half strength on the same interval, while the leaves stay green. They are still making sugar for the tree to store, and nitrogen the roots take up now can be stored for next spring's flush, so a light feed still has work to do. Slowing growth needs less, and heavy nitrogen this late can push soft new shoots that an early frost may damage.

Stop when the season's growth ends: on a deciduous tree such as a trident, when the leaves begin to color; on an evergreen such as a juniper, when cold halts its growth. A tree resting outdoors gets no feed through winter, since its roots take up little in a cold pot and what goes in washes out unused. Course 06, Seasonal Care and Timing, covers the year's calendar and winter care.

You will often read that feeding late in the season makes a tree less hardy in winter, but the evidence is weak. A three-year field study of autumn fertilizing in street and park trees found no loss of cold hardiness in trident maple and two other species, and only small losses in two more (Smiley and Shirazi, Arboriculture & Urban Forestry, 2003). Hardiness builds as shortening days and cooling nights bring on cold acclimation (Course 01, Lesson 13). The plausible risk is heavy nitrogen pushing soft late shoots, and tapering guards against it while the leaves are still at work.

Trees that keep growing indoors

A tropical tree indoors has no winter rest of its own: it grows whenever its light and warmth allow (Course 01, Lesson 13). At the bright window that pace does not follow the outdoor calendar: winter sun reaches the sill and a grow light runs on a timer, while in summer the high sun barely reaches inside, so the ficus (Ficus microcarpa) keeps growing through the year and can even dry faster in winter (Course 03, Lesson 1). Its owner feeds it the 8-4-6 at the label's line for houseplants and indoor bonsai: every 14 days in spring and summer, and every 28 days in autumn and winter “if still growing,” as that line says. The interval comes from the label; whether each feed goes on comes from the tree. If the ficus stopped growing, the feed would wait, and the light would be the first thing to check.

Development and refinement

A plan also follows what the tree is for. Course 02 traced a bonsai's long path: the trunk and roots are grown first, then the main structure is built, then the fine branching is refined (Course 02, Lesson 6). The two courtyard tridents stand at opposite ends of that path, as the figure at the top of this lesson shows.

Development: the label rate, with growth left free

In development, a tree grows freely to build trunk thickness, branches, and roots before fine shaping. The courtyard maple's long low branch is a sacrifice branch: left long and leafy for a season or more, it thickens the trunk below it, and it is removed once that job is done (Course 01, Lesson 12). The new wood is built from sugar the leaves make by photosynthesis, not from fertilizer. Feeding keeps all that foliage supplied with the nitrogen, potassium, and other nutrients it needs to grow and keep working, so that supply never becomes what holds the tree back.

So development gets the full plan: the label's rate and interval while the shoots grow, the taper in late summer, and the stop when the leaves color, as the plan above sets out, with good light and a mix that drains. A stronger can does not thicken the trunk faster. Once the label's supply keeps up with what the growing tree can use, whichever of light, water, warmth, and root health is shortest becomes the limiting factor, and more feed adds salts and soft growth, not thickness (Course 01, Lesson 6). For faster thickening, the levers are more foliage on the sacrifice branch, more light, and a healthy root zone, not a stronger can.

Refinement: lighter, well-timed feeding

In refinement, the work runs the other way: keeping a developed tree's shape fine and compact, with short shoots, small leaves, and dense twigs. Strong feeding while the spring flush extends works against that, giving long shoots with long gaps and large leaves, the coarse growth refinement is trying to avoid. So the display trident gets lighter feeding through the flush: the 8-4-6 at half strength, 4 mL in the 2 L can, on the label's 14-day interval. Once its first flush has hardened, in early summer, it moves to the outdoor line; it then tapers at bud set and stops on the same signals as the courtyard maple, so its leaves stay green and working, building reserves for next spring and for the pruning to come.

There is more than one lighter, well-timed pattern: a weaker can through the flush, as here, or a first feed held back until the first flush hardens, as the simulation below lets you try. Each gives the tree less while its shoots extend fastest, and enough through the rest of the season to keep it healthy. Pruning and light do most of the shaping, though: pinching and cutting back keep the pads compact (Course 09, Pruning and Managing Growth), and strong light keeps internodes short.

Refinement feeding is never starvation. A tree held short of nutrients does not become a fine, healthy small tree: it grows weak, with small, pale leaves and thin shoots, recovers slowly from pruning, and declines (Course 01, Lesson 1). Pale new leaves, or shoots that barely move in spring, are a sign the plan may be too lean, not a sign of good refinement: check the roots and the light, then the record (Lesson 5). Neither pattern is a rule for every species: junipers and pines keep their own rhythms, which Course 12, Developing Bonsai from Starting Material, and Course 14, Refinement and Long-Term Stewardship, cover in depth.

Roots set the pace

Every feed has to be taken up by living fine roots, which spend energy and need oxygen and warmth to do it (Course 01, Lesson 10). Root work, a root zone that dried out, and one that stayed waterlogged all leave a tree with fewer working fine roots, and fertilizer cannot grow new ones. So whenever the roots have been set back, the feed waits for them.

After root work

Repotting cuts roots and strips away many of their root hairs, so the tree is left with only part of its absorbing surface, and fresh cuts take up little. Its regrowth runs on stored reserves and, once the new leaves work, on their sugar, so an early feed cannot speed recovery, and a strong one can harm the roots that remain (Course 01, Lesson 14). The course's starting point is Not now: wait for new roots: hold the feed until new growth shows the roots working, with shoots extending, new leaves of normal size and color, and white root tips at the holes where you can see them. Then begin at the label rate or a reduced one. A reduced rate suits the first feed or two while new roots are only beginning to grow out into fresh mix, as on the balcony trident below; a tree that has been growing normally for weeks since its root work, with white tips at the holes, starts at the label rate. There is no fixed number of weeks; the tree tells you.

Experienced growers differ on this: some add slow-release fertilizer when they repot, as the Royal Horticultural Society's bonsai guide suggests (RHS: Bonsai), and some feed root-pruned trees normally from the start (Evergreen Gardenworks: Fertilizing your bonsai). The course keeps its starting point for the reasons above, and they weigh most for a tree whose roots were heavily reduced, with few fine roots left and no new growth yet: it has little to take a feed up with, so waiting costs it little, while a strong dose can harm the roots that remain. Repotting and its full aftercare belong to Course 11, Repotting and Root Development.

The balcony trident's owner held the feed. By late May its shoots were extending, its new leaves had come out full-size and green, and white root tips showed at the holes when the pot was tipped back on its grid. Its first two feeds were half strength, 4 mL in the 2 L can, a reduced rate while the roots grew out into the new mix, and from late June it moved to the outdoor line every 14 days. Once signs like these hold, waiting longer gains nothing: a tree growing again in a mostly mineral mix, with no feed coming in, will run short (Lesson 1).

After a dried-out root zone

A root zone that dries out kills the fine roots in its driest layers, and watering brings back the water but not those roots (Course 03, Lesson 4). That lesson's rule was Do not feed, and it left when and how to feed again to this course. The answer is the same as after root work: hold the feed until new growth shows the roots working again, with shoots extending at their normal pace, new foliage of normal size and color, and white root tips where you can see them, then resume at the label rate or a reduced one. Never give a catch-up dose for the feeds it missed: a double feed around roots that are only beginning to regrow, in a mix where salts concentrate as it dries, comes at the worst possible moment.

A new arrival

A tree you have just bought or been given is settling into new light and a new place, and feeding does not help it settle (Course 02, Lesson 8). It may not need feeding yet, either: much nursery stock comes with controlled-release granules in its mix, which keep releasing for months, faster in a warm pot (Lesson 3). So a new arrival waits for three things: it has settled, it is growing normally for its kind and the season, and you know what is already in its pot.

To find out, ask the seller what they used and how long it was rated to last, and read that product's label if you can. Look at the surface too: controlled-release granules are small, smooth, round beads, often cream or tan, that swell and then empty as they release; organic feeds are crumbly pieces or cakes; a top dressing is grit or moss (Course 02, Lesson 8). Note what you find in the arrival record. Once the granules are spent, the label plan can begin; until then they are the tree's feed (Lesson 3).

One root problem gets no feed at all until it is fixed: a root zone that stays waterlogged or smells sour. Roots short of air take up little of what is already there, and Lesson 5 shows what to do instead.

Weather changes the plan

Weather changes how fast a pot dries, how fast a feed releases or washes out, and how much a tree grows, so every feeding day starts with the morning check. Four changes come up every year:

• A dry pot on a feeding day. If the lift and the chopstick say the root zone is Drying or drier, and the tree is otherwise fine, the decision is Feed as planned: water first, then feed the moist mix. Water thoroughly with plain water, let it drain until the root zone checks Moist, then feed until a little runs from the holes, as the label directs. Never feed a dry root zone, where the feed would stay concentrated around the roots.
• A heat wave. Pots dry within the day, salts concentrate as water leaves the mix, a sunny pot wall can overheat the roots (Course 02, Lesson 5), and many trees stop growing until the heat passes. A tree that checks dry in that heat, or droops, even in a droop that passes by evening (Course 03's temporary wilting), is under stress, and a feed would add salts to roots already struggling for water. Check it morning and afternoon, and water it thoroughly whenever a check says so (Course 03, Lesson 5); a droop over a moist pot needs no water, only a look at dusk. Either way, the decision is Not now: hold the feed in the heat. Feed again once the heat has broken and the tree is firm and growing, at the plan's rate and with no catch-up dose.
• A wet spell. Days of heavy rain wash part of the last feed out, nitrate most of all, but the next feed on the interval replaces it. Keep the interval rather than feeding early or doubling the next can, and on the day, feed once the mix has drained to Moist (Lesson 3).
• A cold spell. A cold snap in spring slows the roots and the growth, and organic feeds slow most, because the soil life that releases them slows in the cold (Lesson 3). Keep to the plan rather than adding more to make up; if the cold stops growth altogether, the feed waits until growth starts again.

In all four, the plan's rate stays as written, and the weather changes only whether and when the feed goes on. A feed held back for the weather is skipped, not saved up.

Two trees fed for a goal

Feed for the goal follows two matching young trident maples in the courtyard through one season, fed from the same bottle of 8-4-6. Tree A follows the courtyard plan: the outdoor line from when the spring flush is growing, half strength once the shoots stop, and no feed once the leaves color. After a repot it waits for new roots, feeds at half strength, then moves to the label rate.

First set two things for both trees: the Goal, either Thicken the trunk (each tree grows a long, free low branch) or Keep shoots short and leaves small (both trees are drawn compact), and the Roots, Established or Repotted this spring. Then set Tree B's Amount, Plain water, Half the label rate, At the label rate, or Twice the label's strength, every week (four times the label's supply), and its Start, When growth starts, Half strength through the flush, or After the first flush hardens. On a phone, pick B's setting under Change. Under Your call, choose A, B, or About the same, or press Skip. Press Grow the season to run the year from Buds open to Leaves color, and use Pause, Back, Next, Replay, or Skip to the end to stop on any stage. Below the courtyard, a close-up follows the goal (each trunk cut across, or one shoot from each tree), a small lens beside it shows the roots and the feed in each pot, and the readouts Shoots, Leaves, Thickening, Growth, Roots, and In the pot follow the season in words. Find all four challenges to finish. Try these:

1. The simulation opens on Thicken the trunk, Established, and Half the label rate. Make your call, press Grow the season, and compare the two trunk sections at Leaves color.
2. Change B's Amount to Plain water, then to Twice the label's strength, every week, and watch In the pot, Growth, and Thickening in each run.
3. Switch the Goal to Keep shoots short and leaves small, set B's Amount to At the label rate and its Start to Half strength through the flush, and compare Shoots, Leaves, and In the pot with a run at Half the label rate.
4. Set Roots to Repotted this spring, give B At the label rate and When growth starts, and compare Roots and In the pot on the two trees.

With established roots and the goal of a thicker trunk, Tree A at the label rate ended the season with Strong thickening. Half the label rate built Some, with leaves that stayed Green: its In the pot read Short and its Growth Slow, a shortage that shows only in the growth, and the result card called it too lean. Plain water built Little: by midsummer B's leaves were small and Pale all over and its Growth had stalled, because a mix of akadama, pumice, and lava holds little on its own. Twice the label's strength, every week thickened B no more than A. Light, water, and roots had already set the ceiling, so the extra went into longer, softer shoots and larger leaves, and by midsummer B's In the pot read More than the tree can use: salts building, with Browned tips at the roots. A lighter or later start cost B little thickening, because the spring flush runs largely on last year's reserves.

With the goal of short shoots, A at the label rate from when growth starts grew Steady shoots and Full-size leaves, healthy but not the most compact. B at the label rate with half strength through the flush grew Short shoots with leaves close together and Small leaves that stayed Green, with In the pot at Enough all summer: the balance refinement looks for. Holding the first feed until the flush hardened kept the shoots short too, and the label rate after kept the leaves green and working. Half the label rate all season also kept the shoots short, but once the flush had hardened B could use more than it got, and its growth slowed; a refined tree can take the label rate then. Plain water gave small leaves that were pale and stalled, weak rather than refined, and the weekly double-strength feed gave the coarsest growth of all, with salts building. Every refinement result ended with the same reminder: pruning and light do most of the shaping.

With repotted roots, A waited, then fed at half strength, then at the label rate, and showed New white root tips as its growth recovered. B, fed at the label rate from the start, recovered no faster: its new root tips came at the same pace, and its In the pot read Plenty, more than the regrowing roots could use yet, washing out with watering. At double strength every week, its new tips had browned by the time the first flush hardened. In every run, the feed helped only as far as the tree could use it, and feeding early after root work gained nothing.

Let the growth steer the plan