What to do in March

March is an exciting month in the container garden, as the days warm and lengthen, and plants start to put on more vigorous growth again. 

We can also ease those itchy sowing fingers and sow a variety of seeds for an early harvest. But..... most things are still significantly easier to grow when sown later in the year. So there is no harm in holding back for a few weeks. And if you are new to growing, make it easy on yourself and wait until April and May before you sow outside. 

Chillies, peppers or aubergines, on the other hand, are best sown inside before the end of the month (or wait and buy them as plants later in the year). 

The timings here are based on container gardening in the UK, and will also be relevant for many of those growing in other parts of the Northern Hemisphere.  Look out for a seed sowing calendar for your area and use it in conjunction with the advice here.

This month

1. 1. Some Quick Seed Starting Tips
   2. What  to sow outside
   3. What to sow inside
   4. Hunt out slugs :)
   5. Protect your seedlings
   6. What to harvest now
   7. Common questions

A salad of peashoots, sunflower shoots and orach - all grown in March 2022. 

1. Some Quick Seed Starting Tips

• Even cold hardy plants, like peas and spring onions / scallions, will be slow to come up in the fluctuating temperatures if sown outside at this time of year. They will germinate faster and more consistently inside, ideally in a cooler room in your home. Once germinated, move them outside on a warmer day. Try to avoid putting them out if a cold snap is predicted as the dramatic change of temperature can be a shock and stall their growth or even kill them. 
• Good light is key to raising healthy seedlings inside. Put them in the brightest window you can find - and bear in mind that the warmer a room is, the more light seedlings need for strong growth. An LED grow light is a good investment for raising plants inside at this time of year. This is particularly true if you don't have a bright window or live in a warm house. You will find more tips on how to raise healthy seedlings here. 
• When sowing seeds of tender plants like tomatoes and chillies inside, take into account how much space they will take up before it is warm enough to move them outside. Tomatoes, in particular, grow quickly - and little seedlings will soon grow into large plants that will take over your house! 

2. What you Can Sow Outside

The following will survive light frosts and early sowings can be made outside later this month - or sown inside and moved outside once germinated (see note above).  Sowings this month are good way to get some early harvests. But bear in mind there is also a risk that a cold snap will slow growth or even kill them.  Later sowings will often catch up! If you have plenty of seeds, though, there is no harm in sowing a few seeds now - and if the weather is kind they will hopefully grow well. 

• Hardy salad leaves, including: Asian mustards, rocket / arugula, sorrel, and lettuce.
• Spring onions / scallions. 
• Peas and broad beans / fava beans. 
• Swiss chard and leaf beat.
• Kale.
• Carrots (sow in modules or direct in their final pot - they don’t like their roots disturbed).
• Beetroot (sow in modules or direct in their final pot - they don’t like their roots disturbed).
  
• 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.

3. What You Can Sow Inside

Sow the following inside, moving them outside once the risk of frost is over and the temperature is consistently over 10°C / 50°F. Mid to late March is a good time to start sowing tomatoes, but you can wait until mid April if space is limited. Peppers, chillies and aubergines, on the other hand, need a longer growing season and most varieties are best sown before the end of the month.

• Tomatoes and tomatilloes
• Peppers and Chillies
• Aubergines

As mentioned,  tomatoes, in particular, grow fast and quickly take up a lot of indoor space. A good option is to sow a few tomatoes this month (for an early crop) and the rest in April. 

4. Hunt out slugs

The odd slug won't usually do significant damage to established plants - but they can completely decimate baby plants and seedlings. So this is the time of year to be vigilant and keep slug numbers down. 

(Our goal is not to eliminate slugs in our garden - they are an important part of the ecosystem - but to keep the population under control. Most container gardens in urban areas do not have predators like hedgehogs that eat slugs. So we, as gardeners have to remove some of them.)

Hunt out as many slugs as you can: look under pots and in any other cracks or areas they can hide. Go outside after dark one evening, ideally in wet weather (this is when most slugs are visible and active) armed with a torch, and collect them up. Move the slugs you to a local green space (I deposit mine on the grass on the other side of the road!), feed to the birds, recycle in a worm bin, or give to a friend who has chickens. 

5. Protect your seedlings

If you've sown some of your seeds outside, you can protect them form the weather with a cloche or by laying horticultural fleece over them if a cold snap is predicted. Depending on your climate, this may not be necessary, but they will grow faster and stronger, and survive cold snaps better if protected. I don't normally protect mine, which is a bit of a risk, but they normally do OK.  If birds prove to be a problem (I find sparrows like nibbling my seedlings) cover your seedlings with netting or wire mesh. 

6. What you can harvest this month

• Salads. 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. Salad leaves are often at their most flavoursome at this time of year.

A salad harvested in March from the containers in my front yard. 

• Kale, chard and spinach. Established plants will grow strongly this month, too - and excellent harvests are often possible later in the month.
• Jerusalem artichokes. Harvest any remaining tubers early in the month before they sprout again.
• Herbs. Bay, thyme, rosemary, sage and other evergreen herbs can continue to be harvested sparingly this month.
• The first rhubarb is often ready to harvest at the end of this month.

Rhubarb grows well in a large container. This one is about 60 litres / 12 gallons. 

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 exceptions are tomatoes, chillies and aubergines. Because of how long they take to mature, sow early in the year.  Alternatively, you can always buy these as small plants in April or May instead. This is sometimes the best strategy, particularly if you don't have space or a good light windowsill to raise plants inside.

What variety of potato does best in containers?

'First early' and 'Second early', are the fastest potato varieties to grow (ready by June if planted in March) and are the best choice for containers.  They give you the delicacy of new potatoes , 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. Main crop’ potatoes are slower to grow and need larger containers. They produce higher yields later in the year. They need larger containers.  Read how to grow potatoes in containers here. 

What is hardening off and why is it important?

Hardening off is the term for acclimatising plants that are started inside to the colder temperatures and more turbulent winds outside. It's best done gradually - or the change in climate stresses plants and sets them back. Simply put plants outside for a few hours each day on warm days, bringing them it again at night. Slowly increase the amount of time they are outside. Avoid putting them out on very windy days unless you can protect them from the wind. Even hardy plants (those not sensitive to frost) that are sown inside will often benefit from being hardened off. Most plants benefit from hardening and I recommend it. But it is not always essential. If you need to move plants outside without hardening off, try to move them during a warmer, less windy weather spell if you can. The added benefit of moving seedlings outside during the day is that it gives them a healthy dose of outdoor light. You can read more about the value of this and how to avoid spindly seedlings here.

These are some seedlings that I've put outside for a dose of light on a warm day. The lid keeps them protected from the cold wind - but I'll take this off, too, when the seedlings get a bit bigger and stronger. The masking tape on the side of the lid prevents it blowing off in the wind.

Your turn

What are you doing this month in your container garden? I'd love to hear in the comments.