Where the decan sits
Decans divide each sign into ten degree faces. This is the second of Virgo's, starting at ten degrees and ending at twenty, roughly the middle third of the Sun's passage through the sign.
In dates, that is about 2 September to about 12 September. The figures shift a little every year. The Sun's entry into Virgo is not fixed to a calendar date, and the whole set of internal boundaries moves with it, by as much as a day and a half. Anyone born within a day or so of either end is better served by a calculated degree than by a printed range.
Saturn one way, Venus the other
The triplicity scheme takes the earth signs in order, Taurus, Virgo, Capricorn, and gives them the decans of each earth sign in that sequence. Virgo is the second earth sign, so its decans start at Virgo and the middle one falls to Capricorn, whose ruler is Saturn.
The Chaldean order is unrelated to element. It repeats Mars, Sun, Venus, Mercury, Moon, Saturn, Jupiter from the start of Aries, and the seventeenth decan lands on Venus.
Saturn and Venus make for a genuinely mixed picture, and this is a decan where it pays to know which scheme a description is based on. Most short articles online quote one ruler and move on without saying where it came from.
What the blend is read as adding
Virgo through Capricorn is described as method with an end in view. Virgo on its own is read as analysis and correction, sometimes without much interest in where the correction leads; the Capricorn colouring is taken to attach that work to a long structure, a career, an institution, a standard that outlives the task. Older readings call this the most durable stretch of Virgo, meaning the part least likely to abandon a project once begun.
Venus, from the Chaldean side, is read as adding taste to the technique. The traditional associations are proportion, pleasantness and the ability to make a thing agreeable as well as correct, and their appearance here is taken to soften what the Capricorn reading would otherwise make austere. Craft rather than mere accuracy is the usual phrasing.
Treat the whole layer as refinement. Decan work descends from Egyptian star lists and is a real and old part of the tradition, but it modifies a chart reading rather than founding one, and it should not be doing the heavy lifting on its own.
There is one detail worth adding about the modes involved. Virgo is mutable and Capricorn is cardinal, so the triplicity colouring here brings an initiating quality into a sign that is generally described as adaptive. Traditional readings pick that up as a decan more willing to set a direction than the rest of Virgo, which is a small point but it is where much of this decan's reputation comes from.
Not just the Sun, and the boundary question
Decans apply to whatever falls in them. The Ascendant is read by decan very commonly, because it is the point in a chart calculated most precisely from the birth time, and the Moon is read the same way. A Mercury or Moon between ten and twenty degrees of Virgo carries this decan regardless of where the Sun is.
The check above takes your birth date and returns your actual solar degree, along with the decan it falls in and both rulers. For a birthday near 2 or 12 September that is a different exercise from looking up a range, because the range itself is only accurate to within a day or so.
Questions people ask about this
What dates fall in the second decan of Virgo?
Around 2 to 12 September, with drift of up to a day and a half depending on the year. The check on this page works out the degree from your date instead of relying on those figures.
Who rules the second decan of Virgo?
Saturn if you follow the triplicity scheme, through Capricorn. Venus if you follow the Chaldean order. Both are standard, and neither supersedes the other.
Why do descriptions of this decan vary so much?
Largely because of the ruler split. A Saturn based reading emphasises structure and endurance, a Venus based one emphasises craft and proportion. Writers rarely say which scheme they used, so the two circulate side by side.
What does Capricorn add to Virgo?
The tradition reads it as ambition applied to detail, work that is meant to build something lasting rather than simply to be correct. That is an interpretive claim, offered as one.
Does this only matter for the Sun?
No. Any placement sits in a decan. The Ascendant and the Moon are read this way routinely, and the Ascendant especially, since its degree is the most exact figure in the chart.
Should I read my decan instead of my sign?
Read it as an addition. The sign carries the bulk of the description in nearly every tradition, and the decan narrows it. Starting from the decan alone tends to produce a portrait that is very specific and poorly grounded.