Dahlia tasks in March

If you haven't already done so now is the time to start taking cuttings in your heated greenhouse. 
When the shoots are sturdy with two or three leaf joints they are ready to use as cuttings. Use a sharp knife to cut away the shoots a little above their base, where they join the crown. Take care not to cut the crown itself, which would prevent further shoots forming. Trim neatly immediately below a leaf joint, dip in rooting compound such as Strike and plant in either seed trays or pots filled with a gritty seed compost (John Innes Seed) or an equal mixture of peat and sand or seed compost. They may look a little droopy for 7-10 days, this is quite normal! Three weeks on and roots will begin to form. Once the cutting is clearly rooted and showing signs of growth, prick out and pot up in 9 cm pots into a well draining potting compost such as John Innes No 1. We strongly recommend that all purpose or multi purpose composts are not used as they may contain materials that will kill the delicate rooted cutting.

 As you can see in the image some of the cuttings have two leaf nodes and some three.  I don't believe there is a "rule" for this, my own rule is to keep the stem length fairly short and not at all leggy.  Most of the cuttings I take are between 3 and 5 cm.  The exceptions to this are those cultivars that just do not behave and grow not only very quickly but with well spaced leaf nodes.
I have seen other people suggesting cutting most of the leaves away and trimming those that are left, I have no idea what this achieves as we have a success rate of well over 95% of our cuttings rooting when taken as shown above.  Also, I would caution against keeping the cuttings within a polythene bag as there is a real danger of damping off.

Seeds

Towards the end of March any seeds you have harvested should be sown.  Keep the convex side of the seed upwards.  If not the roots will shoot upwards and lose enegy resulting in poor germination.

For those that do not have a heated greenhouse tubers may be started of in trays.