How we test

Every product recommended on this site has been used on my own box, in my own garden, against a real infestation. This page explains what that does and does not prove.

What the test conditions are

One garden in New Malden, Surrey. Roughly 18 metres of Buxus sempervirens hedging planted in 2018, plus six box balls in containers. Box tree caterpillar arrived in 2019 and has returned every year since. The hedge was completely defoliated once, in 2021, and took two full seasons to come back.

Surrey is the worst-affected region in the country, which makes it a good testing ground and a poor average. Infestation pressure here is at the extreme end and the season runs two to three weeks ahead of northern England.

How products get compared

Where I can, side by side on the same hedge in the same week. The hedge runs in sections, which means I can treat one length with one product and an adjacent length with another, under identical weather, at the same infestation stage. That is the only comparison I trust, and it is how I concluded that nematodes are less reliable than Bt rather than simply less lucky.

Where a side-by-side is impossible — you cannot run a controlled trial on a fertiliser without a spare hedge — I say what I observed and how confident I am in it.

What we measure

• Time to feeding stopping. Checked at 24 and 48 hours by clearing the frass beneath a treated section and seeing whether new pellets appear. This is the fastest reliable signal that a treatment is working.
• Whether the damage stops spreading. Photographed from the same position each week.
• Regrowth. Weeks to visible new buds, then months to closed canopy.
• Whether I actually kept doing it. A treatment that demands perfect conditions and a forty-minute routine is one you will abandon in August. That counts against it here.

What we do not do

• We do not quote prices. Amazon's terms require displayed prices to come from their API and be refreshed within 24 hours. Rather than publish figures that go stale, the buttons take you to the current listing.
• We do not use Amazon review scores as our ratings. Every star rating on this site is our own judgement, labelled 'our rating'.
• We do not review products we have not used. There are several nematode brands and several sprayers I have never touched, and you will not find writeups of them here.
• We do not accept payment for placement, free samples in exchange for coverage, or copy approval from any manufacturer.

What we have not tested

Most nematode brands. I have used nematodes twice, from one supplier, and that is not enough to rank a category — which is why the nematode review declines to name a best product and tells you what to look for instead.

I have also not tested the alternatives to box at any scale. The alternatives guide is built on published growing information and the RHS trial at Wisley rather than on my own plants, and it says so.

Why you should be a bit sceptical anyway

This site earns money when you buy things. That is disclosed on every page, but disclosure does not remove the incentive — it just makes it visible. The protection you actually have is that the advice here consistently tells you to buy less: one product rather than five, a refill rather than a new trap, ordinary bark mulch rather than the branded one, and nothing at all if your hedge is healthy.

If you ever find this site recommending something it has not justified, that is worth an email.