This blog is my root veg irrigation recommendation based on our trial (of which you can see more details at my Solargardener blog) and my personal experience.
Carrot, parsnip and beetroot seeds benefit hugely from regular irrigation when they are germinating as do the plants in the early stages of growth. Germination is more even and plant establishment much faster, leading also to fewer losses from slug/snail damage. (I would still recommend sprinkling a few slug pellets prior to germination, but cover with fleece to keep the birds away)
Beetroots can be harvested earlier and will yield much more with continued irrigation, without any loss of quality. Early sown crops will get very large if left in, so a succession of sowings is needed if you like small beetroots.
Although yield is heavier in carrots and parsnips which continue to be watered, there is a loss of skin quality, an increase in splitting and a reduction in root length when watered in accordance with our trial specs (Once every 5 days). In well drained soils continued watering is probably beneficial, but my recommendation would be to try 2 days watering every 2 weeks – a heavy enough application to really soak in, but without the waterlogging associated with more frequent irrigation.
As an alternative to seephose, use drippers spaced about 30cm (12″) apart. Turn the irrigation on to see where the wet patches are. Using a broom handle make a shallow depression in each wet patch and sow 4 or 5 seeds in it. As the plants grow pull the biggest root to eat, but leave the smaller ones to grow on in the extra space created. Weeds are easier to hoe out as you can hoe both ways. Water usage is reduced. The plant tops and roots spread to catch the light and water, so yields don’t suffer much. I have done this with beetroots and it has worked really well. I will try carrots and parsnips next year, but think pulling them one at a time may be more challenging.