Fertilizer burn on plants

The response is water, not more care. Rinsing the pot through is what lowers the concentration around the roots.

Go back over the last two weeks. A feed, a switch to a new product, a top up of slow release granules, or a stronger mix than usual all belong on that list.

Fresh potting mix already carries a supply of nutrients, so a plant fed straight after repotting gets two doses at once. The same goes for a plant just bought, since nursery mix is usually well charged.

A dose that is fine in summer is too much for a plant in a cool, dim room that has stopped growing. The plant takes up less, so more of it stays in the pot.

Hard tap water adds its own salts on top. In a pot that is watered a little at a time and never rinsed, the two build up together.

If nothing was fed and no crust is visible, look at brown tips from dry air and uneven watering instead. Those look similar and behave differently.

Take the plant out of its outer pot and stand it in a sink or a bath. The pot needs an open drainage hole for this to work at all.

• Scrape off any visible crust and any granules sitting on the surface, along with the top layer of mix if it is heavily encrusted.
• Pour room temperature water slowly over the whole surface until it runs freely out of the base.
• Let it drain, then repeat several times over. The water is carrying the dissolved salts out with it.
• Let the pot drain completely before it goes back, and empty the saucer or outer pot.
• Move it out of direct sun for a few days while it recovers, and keep it out of drafts.
• Water normally afterward, and leave fertilizer alone until new leaves are opening cleanly.

If the plant is collapsing rather than showing edge damage, or if a heavy dose of granular fertilizer went in, take it out of the mix instead. Rinsing moves the salts more slowly than a badly loaded pot can afford.

Lift the plant out, shake off as much of the old mix as the roots allow, and rinse the root ball under lukewarm running water. Cut away roots that have gone dark and soft.

Repot into fresh mix in a clean pot only slightly larger than the root ball, water it in once, and let it drain.

Do not feed a repotted plant. Fresh mix carries its own supply, and damaged roots take up little of anything.

Wait for new growth. Clean new leaves mean the roots are working again, and that is the signal to start feeding, not a date on the calendar.

Follow the strength printed on the product you are using, and mix it in a can of water rather than pouring it onto the soil straight. Concentrate landing on roots is what caused the problem.

Feed onto damp mix rather than a dry root ball. Dry roots take up a concentrated solution faster than they can handle.

Rinse the pot through with plain water from time to time through the feeding season, so salts leave rather than accumulate.

Feed less, or not at all, while a plant is not growing. A plant in a cool, dim room in winter uses very little.

Brown crisp edges also come from dry air, from a root ball that swings between bone dry and soaking wet, and from hard tap water building up over months. All three produce edge damage without any fertilizer involved.

Sun damage sits on the leaf surfaces facing the window and is flat and bleached rather than confined to the margin.

The recent history is what separates these. A feed in the last two weeks and a crust on the surface point at fertilizer, and their absence points elsewhere.

Change one thing and watch the next few leaves. Damaged tissue never recovers, so the new growth is where the answer shows up.