Tunç

Something about potatoes makes it not apply, and it is a nice piece of biology: planting a potato is cloning, not breeding.

A seed potato is a tuber — a piece of the parent plant. Growing it produces a genetically identical plant. Every tuber from one plant carries exactly the same genes, so choosing the small ones rather than the large ones selects nothing at all. There is no genetic variation between them to select on.

What makes one tuber big and another small on the same plant is position, resources and chance during that season, none of which is heritable because nothing is being inherited — it is the same individual continuing.

So the character's strategy is genetically neutral. Over any number of seasons the size distribution stays where the variety and the conditions put it.

They do. Potato plants flower, and if the flowers are pollinated they set small green fruits that look like tiny tomatoes — which makes sense, since the two are close relatives.

Those fruits contain true potato seed, and it stores exactly as you hoped: small, dry, viable for years in a jar. A single fruit contains a great many seeds.

Important warning first, because this catches people out: the fruits are not edible. Like the green parts of the plant, they contain compounds that make them unsafe to eat. They look inviting and small children have eaten them. If you are collecting them, say so out loud to anyone else in the garden.

To collect: let the fruits ripen until they soften slightly, mash them in water, let the good seed sink, rinse and dry thoroughly. Same process as saving tomato seed.

Two things weeds genuinely do that get lost in the nutrients argument, one bad and one good.

Bad: they host pests and disease. Several common weeds are alternate hosts for aphids, viruses and fungal diseases that then move to your crop. That is a stronger argument for clearing certain weeds than competition ever was, and it is species-specific rather than general.

Good: they cover and feed the soil. Roots hold structure, prevent erosion and crusting, feed soil life, and pull nutrients up. Bare soil over winter loses more than a weedy patch does.

Which points at the same conclusion from another direction: the question is not weeds versus no weeds, it is what is covering the ground and whether it is competing with a crop right now.

One thing worth ruling out on the established tree while you are looking: ants nesting in the wood rather than travelling through it.

Some ant species excavate galleries in damaged or rotting timber. They do not eat sound wood, so their presence indicates existing decay rather than causing it — but it is worth knowing about, because it points at a problem in the tree that the ants only revealed.

The tell is sawdust-like debris at the base and ants emerging from a specific point rather than travelling the whole trunk. From your description, aphid farming is far more likely.

On the mechanics, and this is the hard part: cutting suckers on your side will not work and can make it worse.

A suckering tree responds to the loss of a shoot by producing more, often several for each one removed. You are pruning it, from its point of view, and the root system supplying them is under someone else's garden and is not affected by anything you cut.

What can work on your side of the boundary:

• A root barrier. A physical membrane sunk vertically along the boundary to a sufficient depth. This is real work — a trench — and it is the only purely physical measure that reliably stops root spread.
• Treating the suckers rather than cutting them, which for a suckering species means an approach that reaches the root system. This is where local regulation matters, since what may be applied and where varies, and near a boundary you need to be careful about drift onto a neighbour's land.

Both are treating a symptom while the source remains.