Hartley Magazine

All the latest news, hints, tips and advice from our experts

March means seed sowing and re-potting!

Still raining? There’s plenty to do in the greenhouse

What a dreadfully wet winter we’re having. I hope that you aren’t suffering too much from the incessant rain from one of the wettest winter’s on record and your garden isn’t too waterlogged, either. Rather than letting the rainwater from the water butts on your greenhouse go to waste, water parts of your garden that are in the rain shadow, which will still be comparatively dry, despite the rain.

One of the advantages of a greenhouse is that it extends the growing season, so plants are growing well once the weather improves. March is sowing time.  Early in the month sow peas, broad beans, lettuce, spring onions, beetroot, kohl-rabi, carrots, chard, leeks, kale and spinach in pots and modules in the unheated greenhouse, as they all germinate at lower temperatures. The label with the name and sowing date, should stay with the plants wherever they go.

Tomatoes, peppers, chillies, aubergines, should have been sown a little earlier, but it is still not too late. Germinate these along with celery, French beans and celeriac in a propagator. Courgettes, cucumbers, squash, pumpkins, can be sown towards the end of the month and kept in the greenhouse until they are planted after ‘hardening off’ once there is no danger of frost. (Dates for the last frost are very variable these days – there have only been three ground frosts in my garden this winter).

Herbs that can be sown too later in the month include. Basil, coriander, dill, chervil lemon balm, rosemary, sage, oregano. There are bedding plants like Ageratum, Lobelia, tender climbers, including Cobaea scandens, the ‘Cup and Saucer’ vine, with a lavender purple flower tube and tender exotics including Amaranthus tricolor ‘Red Army’ boasting flamboyant purple-pink stems, deep purple leaves and deep reddish-purple flower heads, which is wonderful for late colour in the ornamental or vegetable garden.

Some of my cannas have been left in the ground and mulched heavily to protect them through the winter. They are in clay soil which has been improved over the years with plenty of well-rotted organic matter, which has also raised the beds, so they rhizomes aren’t in the heavy clay. Left outdoors, they come into growth later than those which have been stored in the greenhouse, but grow rapidly in hot summers and catch up.  My back up plants in the greenhouse are lightly watered at first, from mid- March, increasing the amount as growth speeds up, once they get growing they are fed with liquid seaweed, as an early season boost. Start watering pelargoniums, overwintered heliotrope and fuchsia, in the same way, giving the latter an early boost with general liquid fertiliser.

It is also time to repot dormant plants like Hippeastrums and houseplants; indeed any plants that are dormant, before they start into growth.  I have a ‘Yuzu’, a relatively hardy citrus hybrid, grown for its fragrant flowers and aromatic rind, will need repotting in citrus compost, too.

Keep a look out for early infestations of greenhouse pests, like aphids and red spider mite and treat them immediately before the problem spreads.  There’s plenty to do when it’s raining outside. Happy gardening!

Aubergine (Black Prince F1) – 5 seeds per 7cm pot, for pricking out

Basil (Sweet Genovese) – 4 seeds per cell (only late in the month)

Calabrese (Green Magic F1) – 1 seed per cell

Cauliflower (for mini cauliflowers) – 1 seed per cell

Celery (Victoria F1) – broadcast in a tray for pricking out later

Chilli peppers (various varieties) – 5 seeds per 7cm pot – only early in the month

Courgette (Parthenon) – 1 seed per 7cm pot

French beans (climbing and dwarf) – 5 seeds per 9cm pot

Kohlrabi (Azur Star) – 1 seed per cell

Lettuce (various types) – 1 to 3 seeds per cell

Oriental salads (mizuna, rocket, tatsoi, etc.) – 5 seeds per cell

Pepper (Roberta F1, Bell Boy F1) – 5 seeds per 7cm pot, for pricking out

Scallions (Parade or Ishikura) – 5 to 10 seeds per cell, depending on how many you like in a bunch

Tomato (Sungold F1 & others) – 5 seeds per 7cm pot, for pricking out.

You can also raise the following vegetables indoors for planting out into your vegetable garden later.

Cabbage (early varieties) – 1 seed per cell

Calabrese (Green Magic F1) – 1 seed per cell

Celery (Victoria F1) – broadcast in a tray for pricking out later

Celeriac (Giant Prague) – broadcast in a tray for pricking out later

Kohlrabi (Azur Star) – 1 seed per cell

Leeks (Hannibal) – 2 seeds per cell

Lettuce (various) – 1 to 3 cells per cell

Onions (Golden Bear F1) – 4 seeds per cell

Scallions (Ishikura Bunching) – 10 seeds per cell

  • Sow aster in a heated propagator for summer and autumn colour.
  • Pot on rooted cuttings of tender perennial plants taken last summer.
  • Sow Ageratum indoors to bring a splash of blue to your summer beds.
  • Start dahlia seeds indoors to produce tubers for lifting in the autumn.
  • Sow Brachycome in a heated propagator – they’re great for filling out baskets and containers.
  • Repot orchids and other house plants before they start into active growth again.
  • Sow Coreopsis indoors or in a heated greenhouse.
  • Sow Celosia in a heated propagator to bring a fiery theme to this year’s beds.
  • Try growing versatile salvia under glass for a long-lasting display throughout the summer and autumn.
  • Sow Cleome on a windowsill indoors as early as possible in the season – it needs fluctuating temperatures to germinate well and this will help ensure it gets a drop in temperature at night.
  • Sow summer bedding plants, such as lobelia, busy Lizzies, petunias and geraniums, in a heated propagator.
  • Pot on hardwood cuttings taken last year.
  • Sow stocks on a bright windowsill for a delicious fragrance in your summer garden.
  • Plant begonia tubers in the greenhouse this month, positioning them just below the compost surface with the indented side facing upwards.
  • Sow your flower seeds now, ready for planting out in June.
  • Start sowing bedding plant seeds ready to plant out after the last frosts.
  • Sow hardy annuals in pots or module trays for planting out later in the spring.
  • Pot up plug plants and grow on in a sunny back bedroom or windowsill. Add some easy feed or plug boost, to give them the very best start. Give the tips a pinch a couple of times while the plants are young, this will make them nice and bushy, with more flowers.