Question 1

What is damping off, and how do you prevent it?

Accepted Answer

**Damping off** is a fungal disease that kills seedlings at or just below soil level — usually overnight, usually just as a tray was coming along nicely, and it is one of the most common reasons a promising sowing collapses.

**What it looks like.** Seedlings **topple over** with a thin, dark, water-soaked constriction at the base of the stem. The top of the plant may still look green and healthy for a while, which is what makes it so disheartening. It typically spreads outward from a patch, taking the surrounding seedlings within a day or two.

**Pre-emergence damping off** is the same organisms killing the seed or seedling before it appears, which simply presents as poor germination — so it is under-diagnosed.

**What causes it.** Several soil-borne organisms, principally *Pythium*, *Phytophthora*, *Rhizoctonia* and *Fusarium*. They are widespread and largely unavoidable in the environment; what matters is whether conditions favour them.

**The conditions that favour it**, which is where all the control lies:

**Overwatering and poor drainage.** The single biggest factor. These organisms need free water to spread.

**Poor air circulation** and high humidity, especially under a propagator lid left on too long.

**Sowing too thickly**, so seedlings crowd each other and airflow at soil level is nil.

**Low light and low temperature**, producing slow, weak growth that stays vulnerable for longer.

**Reused compost, dirty pots and trays**, and water from a butt rather than a tap.

**How to prevent it:**

**Use fresh seed compost**, not garden soil or last year's leftovers.

**Clean pots, trays and the bench** properly before sowing.

**Sow thinly** and prick out promptly.

**Water from below**, and let the surface dry between waterings. A surface that is constantly wet is the problem.

**Remove the propagator lid** as soon as germination is underway, and give ventilation.

**Use mains water** for seedlings.

**There is no cure once it starts.** Remove affected seedlings and their compost immediately, improve ventilation, and reduce watering. Salvaging the remainder by pricking out healthy seedlings into fresh compost sometimes works.

Question 2

What does it mean to harden off seedlings?

Accepted Answer

Hardening off is gradually acclimatising indoor-raised plants to outdoor conditions before planting them out. Skipping it is one of the most common reasons healthy-looking seedlings collapse within

Question 3

Why did my seeds fail to germinate?

Accepted Answer

Almost always one of five things, and the order below is roughly how often each is the culprit. Temperature. This is the most common cause and the least visible. Every species has a soil temperature

Question 4

Why does a plant look worse at home than it did in the garden centre?

Accepted Answer

Because it was grown in conditions you cannot reproduce, and what you bought was a plant at an artificial peak rather than a plant in a stable state. What commercial growing does to a plant: Ideal

Question 5

Why are there tiny flies in my houseplant soil?

Accepted Answer

They are almost certainly fungus gnats, and they are a symptom rather than the problem. Fungus gnats breed in permanently damp compost, so their presence is telling you the pot is staying wetter than

Question 6

Why do my seedlings grow tall and floppy?

Accepted Answer

Tall, thin, pale seedlings that fall over are stretching toward light, a response called etiolation. The plant is investing everything in height to escape shade, at the expense of stem thickness and

Question 7

How do plant diseases spread?

Accepted Answer

Through a small number of routes, and knowing which one a given disease uses tells you exactly which intervention will work — most garden disease advice fails because it addresses the wrong route.

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