March is an exciting month in the container garden, winter is nearly over. As the days warm and lengthen, it’s time to get your compost and containers ready to go. There is also lots you can sow this month. Having said that, for most crops there is no urgency, you still have plenty of time – and many seeds are much easier to start in April or May than they are in March!
An optimistic month, but we still need be vigilant: heavy frosts may return at any time.
The advice here is for container gardeners in the Northern hemisphere. The timings will be good for most of the UK. For those of you in cooler or warmer regions, the timings will be similar but slightly different: I recommend you look for a seed sowing calendar for your area and use it in conjunction with the advice here.
- Get your containers and compost ready
- Slug vigil
- Crops to sow outside
- Crops to sow inside
- Protect your seedlings
- What you can harvest now
- Common questions
- Do I have to start sowing seeds this month? (Quick answer, NO!)
- What potato varieties are best for containers?
- What is ‘hardening off’ and why is it important?
1. Get your containers and compost ready.
Next month you’ll be able to move a lot of your crops outside into their final containers. Now is a good time to start organizing your containers and compost in preparation.
You can reuse old compost to grow most of your crops – you’ll just want to add some fertiliser or worm compost, as all the nutrients will have been exhausted by last years crop.
Although most crops can grow well in rejuvenated old compost, it is much easier to grow tomatoes, aubergines and chillies successfully in new compost. If a good tomato crop is important for you, buy a few bags of new compost now in preparation.
2. Slug vigil
Slugs are most damaging when your plants are small, easily decimating a seedling in one night. There’s few things more dispiriting than waking up in the morning to find all your seedlings have gone (its happened to me, I know!).
By being rigorous about the slug problem now, you will help keep your seedlings safe – and help get the slug population under control for the rest of the season. (Although this is not a magic cure – you’ll still need to be vigilant and keep on top of the problem regularly).
Out of the dozens of different ways to deter slugs, the ‘dusk slug patrol’ is the most effective in a small space. Armed with a torch, you simply pick them off while they’re on the way to their supper.
3. Sow outside
You can sow the following outside – as most will survive light frosts (they are ‘hardy’ in gardening lingo). Starting some crops off outside now can be a good plan, particularly if you don’t have much space inside to raise seedlings. You just need to be aware that if we have a late cold snap, it may ‘check’ (ie slow) the growth of seedlings. When their growth is checked, some seedlings recover and some don’t – in which case you’ll have to sow them again (this happened to my chard, carrots and spring onions last year – they never really recovered, just sat their looking a bit small and feeble!).
Alternatively, you can sow these crops (except potatoes and artichokes) inside and move them outside on warmer days. This can be a good strategy if slugs or other pests are a big problem or if its very cold.
If you’re planning to sow carrots, beetroot, or turnips you’ll want to know that they don’t like to have their roots disturbed. Sow them in their final container outside or in modules inside – so that you can move them without disturbing their roots.
- Salads (Asian leaves, rocket, sorrel, spring onions).
- Peas and broadbeans
- Swiss chard and leaf beat (bright lights or rainbow chard will add vibrant colour and cheer to your container garden).
- Potatoes, towards the end of March. Cover them with a cloche or some horticultural fleece, as the growing tips are sensitive to frost.
- Jerusalem artichokes
4. Sow inside
You can sow the following inside, and move outside once the weather gets warmer (over 10 degrees C) outside. Mid March is the prime time to sow tomatoes, but you can keep sowing them until mid to late April. Peppers, chillies and aubergines need a longer growing season and should be sown as soon possible, and before the end of March if you can.
- Tomatoes and tomatilloes
- Peppers and Chillies
5. Protect your seedlings
If you’ve sown some of your seeds outside, you’ll want to protect them if a cold snap is predicted. Although some seedlings will survive frost without protection, they will usually grow faster and stronger with it.
You can protect your crops with cloches (eg upturned water cooler bottles or hoops covered in plastic) . Or you can buy, at low cost, ‘horticultural fleece’, which you just lie over your crops.
6. What you can harvest now
If you sowed winter salads in August / September last year, you will notice that they begin to grow faster again as the day lengths get longer and the temperature warms. The leaves always seem particularly tasty at this time of year – and they make a very welcome change from root veg!
7. Common questions
Do I have to start sowing seeds now?
No. You can happily wait until April or May. Seeds will be more willing to grow then and you’ll still have time to start most things off. It’s a lot easier to grow from seed later in the year so if you’re new to growing you may want to try this… or at least don’t be hard on yourself if your early sowings don’t all work out.
The exception is tomatoes, chillies and aubergines, these do need sowing now – but you can always buy these as small plants in April or May instead (also a good a strategy if you don’t have a light space to raise seedling inside).
What variety of potato does best in containers?
Potatoes are categorised by how quickly they grow and mature. ‘First earlies’ are the fastest to grow (ready by June if planted in March), ‘main crop’ grow bigger, and produce higher yields later in the year. For containers, First or Second Earlies are a good choice: they take up less space than main crop varieties, give you the delicacy of new potatoes earlier in the year, and, because you can harvest them in June, free up big pots to grow other crops in (like courgettes or runner beans) over the productive summer months. You can sow them outside from mid to late March.
What is hardening off and why is it important?
This is the term for acclimatising plants that are started inside to the colder temperatures and more turbulent winds outside. This needs to be done gradually – otherwise they may die or be severely set back by the shock.
Plants that are sensitive to frost need to be kept inside at night and on cold days, but, with care, can be put outside – ideally under a cover of some sort – for a breath of fresh air on warmer days. Slowly increase the amount of time they are put outside over two or three weeks, moving them permanently once all risk of frost is over.
Even hardy plants (those not sensitive to frost) that are sown inside need to be hardened off gradually – although they can be planted out before the risk of frost is over.
Moving seedlings outside during the day also gives them a healthy dose of full-on daylight (you can read more about how to avoid spindly seedlings here).
What are you doing this month in your container garden? I’d love to hear.