March
Written by Nelly Hall
March Greenhouse Growing Guide – Nelly Hall
It’s all systems go this month! Spring at last – after a long and painstakingly slow winter, the signs of the new season are finally emerging. The stirring energy beneath the soil and in the greenhouse is unmistakable, making it the perfect time to get started with March growing. With longer daylight hours ahead, spring sowing is in full swing, bringing new life to gardens and greenhouses alike.
Early Spring Sowing
The daylight hours are on the rise, and we get a glorious increase in light this month – and that wonderful day on March 30th when we jump the clocks forward and create evening light again!
The greenhouse is now packed – the joy of continually emerging new seedlings jostle for space beside potted on seedlings, and pots of herbs and salad leaves. As well as the mostly successful first overwintering of my new love – pelargoniums!
We get going early in our growing at Alitex to show what you can achieve with a greenhouse during the winter months and early Spring when outdoor gardening takes a back seat. Our aim is to keep our show structures looking great and have plants that we can use for our show season and can transport from show to show.
Our main jobs this month are sowing, potting on – getting creative with containers, and pest control. And trying to create as much space to accommodate that as we can!
Sowing first, I love Charles Dowding seed trays; they are the best for any seeds of a decent size. Pack the trays with peat free compost, pop the seed in and job done – when ready to pot on, or plant out, you just push your finger through the hole and the neat little plug pops out ready for the easiest potting on.
This month I will have 2 sowing hats on. First is flowers, herbs and salads for the upcoming shows and to use around Alitex HQ. We are sowing a range of terracotta pots – I love the wide shallow
Mizuna and mustard mixed together, as well as spinach for baby leaves and lots of rocket from now until the end of the year. I also like to sow lettuce such as Lollo Rosso in different shades of red and green and pot on into low trough-like zinc containers as they look stunning in the greenhouse and can be moved in and out according to the weather.
I love nasturtiums and greenhouses aren’t complete without pots of these
through the summer, I am trying a few new ones this year – looking forward to
seeing ‘Ladybird Rose’ this summer! I plant them in some more interesting
containers – old vintage gems that I collect from some wonderful local shops –
and use sticks for them to scramble up and put them on our strawberry boards
for them to tumble down at the same time.
We will also be sowing cosmos, cornflowers and seeing if my own collected Corncockle seeds germinate.
Supermarket basil hack
Julia Parker’s supermarket basil hack has now become a firm favourite, and I start this from now throughout the summer to have a steady supply of basil – along with tomatoes, the absolute scent of summer!
Sowing for home and work
My second sowing hat is veg. Some for work, but also some for home. I will be
sowing peas – thickly in pots for pea shoots, and into the next empty seed tray for the veg garden.
Greenhouse and veg patch crops
I will sow chillies, courgettes, peppers, which will live in the greenhouse for the
summer, and fennel, chard, cabbage and calabrese which I will transfer into the veg patch. I am looking forward to trying Mark Diacono’s thousand headed kale this year.
The Importance of Potting On
Potting on is a necessary part of this time of year, but those seed trays I have
mentioned make that job so easy. I suggest not leaving it too late – they will
fill their root space rapidly at this time of year and you allow them to really
establish & thrive by giving them enough root space.
Pest Control and Vigilance Greenhouse and veg patch crops
The final and probably one of the most important jobs this month is pest control.
You need to do a daily pest check to stay on top – as your crops grow they are creating a wonderful feast for aphids and slugs. Lifting pots to check for sneaky slugs hiding beneath and checking your seedlings for the first sign of tiny white fly is a daily ritual. We do not kill slugs – they get put outside and the local bird population seem to arrive to take over slug control operations. There are several ways to tackle the aphid arrival, soap spray, SB Plant invigorator, ladybirds – even
carnivorous plants, so take your pick. But be vigilant!
Greenhouse and veg patch crops
Finally it is a great month to take moments to appreciate the shift in seasons. Its been a gloomy winter, and any chance to have the sun on your face, and get your hands in the soil is a blessing. There is always room for a chair in a greenhouse, taking a pause – a good cup of coffee or a tipple of your choice is a wonderful ritual to establish to appreciate your labours and watch it unfold around you.
Thanks for reading this March Growing Guide! With longer days and fresh energy in the garden, now is the perfect time to get sowing. Whether you’re filling your greenhouse with vibrant seedlings or prepping for a thriving veg patch, careful planning and potting now will set you up for success in the months ahead. Happy spring sowing!
FAQs: March Growing Guide
March is when conditions finally begin to work in your favour. Daylight hours increase noticeably, soil starts to warm, and plants respond quickly to the change in light and temperature.
What makes it different from earlier months is reliability. Seeds sown now are far less likely to struggle or stall, and growth becomes more consistent. It’s the point where the garden shifts from waiting to actively moving forward.
March is one of the busiest sowing months, particularly under cover where you can control conditions more effectively.
You can begin sowing a wide range of crops, including:
- salads like rocket, spinach, and mustard for quick harvests
- herbs such as basil (with some warmth)
- vegetables like chillies, peppers, and courgettes
- flowers including cosmos and cornflowers
The greenhouse allows you to build momentum early, giving plants a strong start before outdoor planting becomes viable.
Seedlings grow quickly in March, and what starts as a small tray can become overcrowded in a short space of time. If left too long, roots become restricted and plants begin to compete for nutrients and light.
Moving them into larger pots at the right stage gives each plant the space it needs to develop properly. It also reduces stress and leads to stronger, more balanced growth as the season progresses.
The clearest sign is when seedlings develop their first true leaves, which appear after the initial seed leaves. At this stage, the plant is actively growing and beginning to need more space.
You may also notice roots starting to fill the tray or plants becoming crowded. Acting early helps maintain steady growth, rather than waiting until plants begin to struggle.
Early enthusiasm can sometimes lead to avoidable issues. March is productive, but it still requires a bit of control and awareness.
Common mistakes include:
- sowing too much at once and running out of space
- leaving seedlings too long in trays before potting on
- inconsistent watering, especially in a greenhouse
- not allowing enough airflow, leading to pests or disease
Keeping things manageable is just as important as getting started.
As new growth appears, it quickly attracts pests looking for fresh, tender plants. In a greenhouse, where conditions are sheltered, pests can establish themselves very quickly if left unchecked.
Regular checks make a big difference. Catching early signs of aphids, whitefly, or slugs allows you to deal with the problem before it spreads, rather than trying to recover damaged plants later.
Some hardy crops can be sown outdoors, but conditions are still variable. Cold soil and sudden weather changes can slow germination or damage young plants.
For most gardeners, it’s more reliable to start seeds under cover and transplant them later. This gives plants a controlled start and improves their chances of establishing successfully once moved outside.
March often leads to a crowded greenhouse very quickly. With new sowings, established seedlings, and overwintered plants all competing for space, organisation becomes essential.
Rotating plants, using different container sizes, and moving hardy seedlings outside during milder days can help free up room. Staying on top of spacing ensures plants get enough light and airflow, which is just as important as watering and feeding.
