The Celtic Solar Calendar

The author (Michael Vescoli) developed the "Celtic Solar Calendar" using the
sacred Druid trees to be used with solar configured astrology placing more
importance in the Greco-Roman Zodiac rather than the Celtic Lunar Zodiac of
Helena Peterson.

In the construction of the Celtic tree circle we find 29 'Egyptian weeks'
(the Egyptians originally divided the year into 36 large weeks of 10 days and
one small week of 5 days) and the question is: where does the number 29 come
from?  The Celts certainly knew the solar month, the time span between two
consecutive transits of the moon of the meridian of the vernal equinox.  It
last just over 27 days.  On the other hand, they were also certainly familiar
with the synodic month, the time span between two similar phases of the moon.
 This lasts for about 29 days.  We could leave it at that.  But whilst we are
wondering why the period of the walnut tree lasts for 19 days, the yew, which
was driven out, steps into the breach. The yew takes up nine days.  Thus the
walnut has only ten days left instead of 29, we now have 30 periods of ten
days.  This fits in well with the number three, the favourite number of the
Celts.  So we have 300 days accounted for. Then we have the time to assign to
the poplar: a short week in February (five days), 14 days in May (a
fortnight) and nine days in August, which makes 28 days.  The elm has 13 days
in January, which is the number of consinants in the Beth-Luis-Nion, and 11
in July.  Now all we need is the nine 'secret' days of the yew and one day
each for the oak, the birch, the olive and the beech for a total of 365 days.

Thus we arrive at :

Oak (21 March)

Hazel (22-31 March)
Rowan (1-10 April)
Maple (11-20 April)
Walnut (21-30 April)
Poplar (1-14 May)
Chestnut (15-24 May)
Ash (25 May - 3 June)
Hornbeam (4-13 June)
Fig (14-23 June)

Birch (24 June)

Apple (25 June - 4 July)
Fir (5-14 July)
Elm (15-25 July)
Cypress (26 July - 4 August)
Poplar (5-13 August)
Cedar (14-23 August)
Pine (24 August - 2 September)
Sail, the Willow (3-12 September)
Lime (13-22 September)

Olive (23 September)

Hazel (24 September - 3 October)
Rowan (4-13 October)
Maple (14-23 October)
Walnut (24 October - 11 November)
Yew (3-11 November)
Chestnut (12-21 November)
Ash (22 November - 1 December)
Hornbeam (2-11 December)
Fig (12-21 December)

Beech (22 December)

Apple (23 December - 1 January)
Fir (2-11 January)
Elm (12-24 January)
Cypress (25 January - 3 February)
Poplar (4-8 February)
Cedar (9-18 February)
Pine (19-29 February)
Willow (1-10 March)
Lime (11-20 March)

From "The Celtic Tree Calendar" by Michael Vescoli