IBonds and other savings bonds are unique in that they have a fixed principal and variable maturity. You can redeem them anytime after one year, after five years without the three month interest penalty, and after thirty years, they stop earning interest.

With IBonds you can purchase whenever you have a need in your portfolio and the fixed rate appears favorable. You can always redeem them later if the current fixed rates are higher. Also, you can redeem them in a manner to manage your tax liability in any given year.

The purpose of laddering is to allow you to have a percentage of your fixed maturity securities (Bills, Notes, and Bonds) mature each year. With a laddering of say five year notes, you could buy 20% of your allocation each year and rollover that amount each time it matured With the reduction of the minimum purchase amount to $100, you could easily buy monthly even for small portfolios.

With the exception of IBonds, you are really better off buying treasuries in retirement accounts. Only some custodians allow treasury purchases at auction without charge.