January is the first calendar month of the New Year, but it is not necessarily the first month of action, weather is the prime shaper of actions taken and actions needed. If there is snow on the ground or your garden is flooded then send off for catalogues and plan to commence in February. No point doing more harm than good by working out in weather that is not conducive to growth or task.
The thing to consider in January is that milder wetter winters may be provoking some early showings in the garden from spring bulbs or consequently have prolonged late season blossoms and berries but don't let that trick you into full steam ahead planting of edible crops; there could be harsh frosts in a day or two. If you have the New Year eagerness upon you then the most important thing is get the site right. Chose a place to grow your veg that gets good light and is not too breezy, (wind makes plants need more water as well as damages foliage). If gusty put up a fence or hedge to shelter.
There are prep tasks to be achieved; setting out the site, making raised beds, positioning a trellis or support system for beans or raspberry canes. No amount of enthusiasm can reverse the fact that seed in soggy ground or solid ground will not germinate. Be it January or November, digging over wet ground will just help make slop when the next rainfall comes, digging over solid ground to make fine tilth for sowing is not the best expenditure of your energy. Think instead of covering the ground with compost and manure which will add nutrients and bacteria that will both increase the fertility of your soil and via the action of earthworms and other beneficial insects and garden organisms will physically improve the structure of your soil. Add a layer of membrane over that and you will heat your soil up in the coming weeks, enough for February sown seeds to think it is March. If you have a polytunnel or greenhouse you can start many edibles off under protection. Even a window sill will suffice; you can sow and grow-on via module trays until planting out time in Feb/March.
Sometimes February is the coldest month of the year. Ice or not. Sometimes it is the wettest; if not in actual direct rainfall them simply in the saturation of the soil, a moisture level that has been building all winter, so don't over walk the garden, work off a plank if you can. Compaction of the soil is likely with soggy soil and in compaction nutrients are less available and root growth will be stunted, doubly setting you back. On the bright side, light levels are improving and spring is on the doorstep. It is the ideal month to lay out the garden if you missed that trick in January. While you are laying out what and where to plant, always remember that crop rotation is the key to continued success in the years rather than just single year ahead and that raised beds are the easiest way to manage fertility and soil structure for healthy veg. Crop rotation is simply not planting the same vegetable in the same position in two consecutive years (aim to have quadrants of four and move clockwise with plantings), it keeps the plant moving ahead of diseases that can linger in soil and lets you manage fertility more efficiently too.
Parsnips need to be harvested in early March before they start into re-growth and now is also the time to get up the last of leeks (they will freeze well) and pluck too the last of the late Brussels sprouts (also a good freezer) . To hand will also be chard, spring cauliflower & cabbage, kale, salsify and scorzonera, spring onions and leeks. If fresh to edible gardening then you can commence with the knowledge that March is traditionally associated with planting potatoes and is also the month for crowns as well as tubers so you could also start a corner of Jerusalem artichokes and establish an asparagus row. It is the ideal time to direct sow root crops (Beetroot, Turnips, Radish, Parsnips and carrots etc) but also to start early peas and broad beans, and under cloches or fleece try lettuces, summer cabbages, early cauliflowers, Brussels sprouts.
If you don't have a crop of comfrey (Symphytum ×?uplandicum or S. officinale) on the go then consider starting one; the first cut of comfrey at this time of the year is often utilized as a fertilizer under seed potatoes to boost the future yield and the fermented tea is a wonderful tonic for all edibles at any stage of the year. Late march and early April is a great time to harvest nettle tops for nutritious and tasty soup but nettle parts soaked in a bucket for three weeks makes a brilliant foliar feed with the boon of being a pesticide to booth, and can be made in all months that nettles are about.
April - this is a month where we are really 'motoring'. Every day the light is getting better, longer and stronger. You will see it in the mounting vigour of previously planted crops. You will feel it in your own eagerness to get on with tasks and to get new edibles started. Plants are photosynthesizing like crazy and the temperatures are lifting but sudden cold snaps can be a problem this month and it hit fresh vigour hard so be vigilant and wrap tenders with horticultural fleece if cloud cover is absent at night.
April can be the month that reveals a 'Hungry Gap', this juncture between the last of the winter crops and period that is just a litter prior to the availability of early summer crops. It reminds us that now is the time to sow and there is always a lot to sow this month, especially if March has been a wash out or a freeze out. Think of a vegetable and it can be sown this month. It's not too late to sow seeds with sow in February or March written on them and it's not too early to start (under cloche or greenhouse/windowsill) May seeds either.
It is not all about seed and April will see plugs (seedlings and baby plants) available in garden centres alongside tubers, sets and crowns. So do plant out Asparagus, Globe Artichokes, Jerusalem Artichokes, Potato, Onion sets, Shallot Sets and Strawberries. Strawberries and potatoes do not like to share a bed or follow each other in rotations; they inhibit each other and can pass on pest/diseases. On the subject of pests, or more to the point, nuisances; just as the warmer weather and moisture has crops springing into action, so too are the weeds. If you are glass half full person then remember many weeds are dynamic accumulators; basically they absorb really good nutrients from the depths of the soil and as long as they are deprived of a chance to re-root (mash up or dry out their roots) they will rot down and bestow back all that nutrition to the soil or compost heap.