R; package {stats}; function {ts.plot}; change x-axis labeles

I need to change the x-axis labels so they are words instead of numerals. Currently, the x-axis goes 1, 2, 3, etc. I would like it to go "Placement", "Fresh", etc.

    trendplot <- function(timeseries, color, index, first = FALSE, w = 4, add_main = ""){
  if (first) {
    plot.ts(timeseries[, index], col = color, lwd = w,
         ylim = c(-2, 2),
         ylab = "Scaled Relative Abundance",
         xlab = "Stage",
         main = paste0("Trend Plots", add_main)) # gsub(".", " ", colnames(timeseries)[index], fixed = TRUE)
  } else {
    lines(timeseries[, index], col = color, lwd = w)
  }
}

Update: This code works for what I wanted it be.

stages<-c('Placement','Fresh','Bloat One','Bloat Two','Post-Bloat One','Post-Bloat Two')
trendplot <- function(timeseries, color, index, first = FALSE, w = 4, add_main = ""){
  if (first) {
    plot.ts(timeseries[, index], col = color, lwd = w, axes = FALSE,
         ylim = c(-2, 2),
         ylab = "Scaled Measurement",
         xlab = "Time Point",
         main = paste0("Trend Plots", add_main)) # gsub(".", " ", colnames(timeseries)[index], fixed = TRUE)+
  } else {
    lines(timeseries[, index], col = color, lwd = w)
  }
  {axis(1, at=1:6, labels=stages, cex.axis=0.5)}
}
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