Rex

Good breakdown. The rule of thumb is that mobile nutrients show on old leaves first because the plant robs them to feed new growth, and immobile ones show on new leaves.

Check for a reservoir you have forgotten: a cover pot with standing water, a propagation jar, a saucer under the radiator. Eight plants in one room with a persistent population usually means one wet thing is breeding most of them.

The dig test is underrated. I thought I was watering deeply for two seasons and my wet zone was about the size of a mug.

Two metres into a room is a much bigger light change than it looks, often 70 to 80 percent less light, because light falls off with distance and the window frame narrows the angle. A fig responds by shedding the leaves it can no longer afford to run, and those are always the lowest and oldest. Dropping one a week for six weeks is it balancing its budget, not dying. Move it back toward the window but add a sheer curtain instead, which cuts the scorch without cutting the light, and expect the drop to stop within a fortnight.

Phone apps read in the wrong units and average across the frame. If you want a number, measure at the leaf pointing back at the light source, and compare readings between spots rather than trusting the absolute value.

Wait. Feeding a plant that is not growing just salts the root zone. If you want to do something useful, put a dark mulch or a cut fabric square around the base to warm the soil a few degrees.

Peppers sulk. They are a warm soil crop and below about 15C at night they essentially idle: roots barely extend, no top growth, and the leaves often go a darker green than usual. The moment you get a run of warm nights they take off, and by mid-season nobody can tell which ones stalled. Dark green and alive after three weeks is the good version of this story.

Hold off on fertiliser for at least two months. Fresh roots are easy to burn, and a plant with no growth has no demand for nutrients anyway. This is the single most common way people finish off a plant they nearly saved.

The dome coming off at germination rather than later is the bit I had backwards. I assumed they needed the humidity while small.

That is unpollinated fruit aborting, not a disease. Squash carry male and female flowers separately, the female has a tiny fruit behind the flower, and if she is not pollinated in the few hours the flower is open the plant drops the investment. Go out between 7 and 10am, pick a male flower, strip the petals, and rub the anther directly on the female's stigma. Two females per male is fine. You will know within 48 hours because a pollinated fruit visibly swells rather than softens.

The bluish hunched look on brassicas after transplant is usually phosphorus being temporarily unavailable in cool soil rather than a real deficiency. It corrects itself as the soil warms and roots extend. I would not add anything.

Test, in your specific case. One bed behaving differently from four identical neighbours is exactly the situation a test resolves and guessing does not. Purple brassicas with fine beans hints at phosphorus availability or a pH problem, and if your pH is off, adding compost changes almost nothing while lime or sulphur fixes it for years. If all five beds were equally mediocre I would say skip the test and just feed them.

That is a good outcome, honestly. Expect no new growth for six to ten weeks while it rebuilds roots, keep the light the same, and resist the urge to fertilise it back to health.

Permanently damp soil in a plastic pot with bagged compost is the actual problem, and the brown edges are the symptom of roots that cannot drink rather than a plant that has not been offered water. Compost that stays wet for three weeks is compacted and has no air in it, roots suffocate, damaged roots cannot move water to the leaf margins, and the margins die first because they are furthest from the stem. Take it out of the pot and look: healthy monstera roots are firm and pale, bad ones are brown, soft and smell sour. If they are bad, cut them off, repot into something chunky with bark and perlite mixed through, and water thoroughly but only when the mix is nearly dry throughout.

Bagged topsoil is the other half of the problem. It is usually screened but still full of small stones and clay clods that break the taproot. I ran mine through a 10mm sieve for one bed as an experiment and the difference in straight roots was ridiculous.

Use a slightly chunkier mix than you would in summer. In weak winter light the mix's ability to dry is doing half the work of keeping the roots healthy.