Optimum Sowing Times for Irish Gardens

I have had a number of mails asking about optimum sowing times for the rest of the season. Always eager to please, I have included my best shot below for what works in my garden in Sligo. If you are based further south you may be able to go a bit earlier by 1 or 2 weeks for some crops, but I would say if you stick to the below you won't go far wrong.

I have also included germination temperatures and times which are handy to know if you're fretting that your seeds haven't come up. Bear in mind that germination temperatures mean both day and night: so even though it can be warm in a greenhouse at this time of year, it'll still be too cold at night. Also: the warmer seeds are the quicker they will germinate, so you could go up by a few degrees if you're in a rush.

All the below refers to sowing in trays under cover, unless otherwise indicated.

Aubergine

Sow: February to March. I would advise that, once you get into March, sow a mini fruit variety like 'Jewel Jet' because larger fruit may struggle to ripen (in Northern gardens).

Germination Temp: 20 - 25˚C
Germination Time: 7-10 days

Sow in modules and pot on 4 weeks later into 7cm pots. Pot on again to 10cm pots 10-14 days later if not ready to plant out. Seedlings must be kept above 14˚C.

Plant mid May/June in greenhouse or polytunnel.

Broad Beans

Sow: in Feb/March; they can be sown in November for earlier harvests the following year, but I must say I never had great success with this. Sow in trays with larger modules, e.g Huw Richards trays or Rootrainers.

Germination Temp: 14˚C +
Germination Time: Up to 2 weeks.

Plant out after 3-4 weeks if sown in modules. Get them planted out as soon as they are large enough; they don't do well hanging around in trays.

Can take up to 2 weeks to germinate. Soaking speeds things up, as does increasing temperature.

French Beans

Sow: middle of May under cover, early June outside.
If growing in the polytunnel, they can be sown late April (much more reliable in cooler gardens).

Sow in a tray with a larger module, e.g Huw Richards trays or Rootrainers.

Germination Temp: 20˚C
Germination Time: 7-10 days

French beans don't like cold and will be killed by frost, so they need to be protected. I recommend covering with fleece for the first 2 weeks when planting outside, even in June.

You also need uninterrupted growth, so plant 3 weeks after sowing so that roots don't get constricted in trays.

Beetroot

Sow: February under cover if not too cold; early March is better until late June. You can sow in July if you're happy with smaller beetroot.

Germination Temp: 20˚C
Germination Time: 5-14 days

Sow 3 or 4 seeds per cell in a 45mm cell tray, e.g. Huw Richards. Thin to 4 seedlings per cell and plant out under fleece 3 weeks later.

Broccoli

Sow: mid February to March for summer cropping purple broccoli varieties. Sow in June for overwintering and cropping in March/April of the following year.
Sow mid February to July for calabrese.

Germination Temp: 18˚C
Germination Time: 3-7 days

I find the quality of the young seedling makes a significant difference to the vigour of the finished plant. I would sow more seeds than you need and choose the very best; we're expecting a lot from both calabrese and purple broccoli, so give it your best shot.

Early sowings should be covered by fleece when planting out.

Brussels Sprouts

Sow: April/May. Sowing too early gives sprouts in autumn rather than winter.

Germination Temp: 19˚C
Germination Time: 3-7 days

As with broccoli, it's better to sow more than you need and pick the best.

Cabbage

Sow: Pointed cabbage - February/March for a May/June harvest.
Autumn ballheads - Sow in May
Sow in July for winter savoy harvests.
Spring cabbage - sow August for April/May harvests.

Germination Temp: 18˚C
Germination Time: 3-7 days

Protect early sowings with fleece when planting out, then mesh to protect from cabbage root fly.

Chilli & Sweet Peppers

Sow: Mid February to mid March; sweet peppers as early as possible.

I sow multiple seeds in small trays, and prick out and pot on after 2-3 weeks. This is handy because it takes up less space - plus leggy seedlings are likely from early sowing at relatively high heat and low light; you can bury long stems when pricking out and potting on to strengthen the plant.

Germination Temp: 20-25˚C
Germination Time: 7-14 days, warmer is quicker.

Carrots

Sow: March outside; February if growing in the polytunnel.

I always sow direct outside (not in trays), but it's a good idea to protect from slugs and ensure there are no slug habitats nearby, as seedlings can easily be eaten before you've noticed they've come up. I cover the bed with fleece with edges well secured; this seems to do the trick and it also speeds up early growth.

Germination Temp: 10˚C +
Germination Time: 10-14 days

Cauliflower

Sow: in February for early to midsummer harvests.
Sow May - June for autumn heads.
Sow in July for overwintering biennial varieties (which crop the following March or April).

Germination temp: 18˚C
Germination time: 3-5 days

Cauliflowers from a single sowing mature at the same time and (especially in summer) don’t hold for long without going into flower. It can be difficult to chow through multiple cauliflowers, so it's a good idea to stagger sowing every couple of weeks for a longer harvest period.

Protect early sowings with fleece when planting out, then mesh to protect from cabbage root fly.

Kohl rabi

Sow: February for early summer harvest.
Sow in July for mid autumn to late winter harvests.

Germination Temp: 18˚C
Germination Time: 3-5 days

Kohl rabi goes woody in early summer - so don’t sow later than February.

Protect early sowings with fleece when planting out, then mesh to protect from cabbage root fly.

Celery & Celeriac

Sow: Mid march for summer celery.
Sow April to early May for autumn celery.
Sow mid March for celeriac.

Germination Temp: 20-25˚C
Germination Time: 10 - 14 days

Both take around 10-14 days and need light to germinate, so it's better not to cover seeds with compost. I sow in small trays and cover with a plastic bag to keep moisture in.

Germination will be much quicker if you go for 25˚C.

Swiss Chard & Perpetual Spinach

Sow: Chard and perpetual spinach flower in early spring, so March sowings will have a significant number of plants run to seed before you get many leaves. April to early May is much better, and will produce leaves right through till winter.

A June sowing will give a fresh stock of plants for autumn/winter - and some early leaf harvests before flowering the following spring.

Germination Temp: 20˚C
Germination Time: 5-7 days

Courgette & Summer Squash

Sow: These plants thrive with plenty of warmth (and really struggle in the cold), so there is no advantage to sowing early. Mid April is the earliest I would suggest - and warm enough in an unheated greenhouse or polytunnel for plants to shoot off.

Remember to protect from cold or frost at night. You could even bring plants into the house at night if frost is forecast.

Germination Temp: 20-25˚C
Germination Time: 5-7 days

Plant out in mid May or later if there is a risk of frost. An early May sowing might be better in more northern gardens, as frost can be about until mid June.

Cover with fleece either way to protect for the first couple of weeks - this will also help plants establish quicker.

Cucumber

Sow: Same notes apply to cucumber as courgette: mid April is the earliest I would sow.

Germination Temp: 20-25˚C
Germination Time: 5-7 days

Seeds can rot in overly watered compost; mix with 50% perlite or vermiculite to be on the safe side. A smaller sized seedling tray cell (e.g. Charles Dowding trays) is good for sowing; then transplant to a 7cm pot.

Pot on until ready to plant indoors in mid May, making sure to protect from frost. Outdoor ridge cucumbers aren't planted out until mid June, so they will need to be potted to progressively larger posts until they can go out.

Florence Fennel

Sow: no later than February for spring crops; otherwise they will run to seed before you get a good size bulb.

Second sowing in July, up to the first week of August.

Germination Temp: 18˚C
Germination Time: 7 to 10 days

Plant out February sowings 4 weeks later and cover with fleece for protection. July sowings will be ready to plant out in 3 weeks in warmer summer temperatures.

Kale

Sow: March - August

Earlier spring sowings grow larger leaves when maturing in summer warmth; these are better for cooking as they are less tender.

June/July sowing results in smaller, more tender leaves in late summer and autumn. Kale is very frost tolerant and will happily stand in the garden all winter: a valuable crop all year round.

Germination Temp: 18˚C
Germination Time: 3-7 days.

Plant out 3-4 weeks after sowing. Protect early planted crops with fleece.

Leeks

Sow: Better to sow later as this reduces the chance of flowering in summer. Early April is the optimum time and you can sow as late as early May.

It's handier to multisow 4-5 seeds in each cell and plant out as a group. You can also broadcast sow in fish boxes, which is kind of fun and produces nice large transplants - though it is a bit more work.

Germination Temp: 18 - 20˚C
Germination Time: 5-10 days

Transplant 6 - 10 weeks after sowing.

Lettuce

Sow from February to early autumn. 4-5 sowings can give lettuce up to late autumn by picking leaves rather than the whole plant.

Germination Temp: 18˚C. Won't germinate if night and day temperatures are above 26˚C; 'night and day' is key here as it will germinate in temps higher than 26˚C provided nights are cooler.
Germination Time: 2 - 6 days.

Transplant 4 weeks after sowing, early crops can be protected with fleece but, after May, will get too hot. Use mesh if protection needed after that.

Melon

Sow: 2nd week in April. It's often recommended to sow earlier but, like cucumbers, they grow fast in warmer conditions with plenty of light. Earlier sowings need a lot of looking after and will not gain much over later sowings, which catch up quickly.

Germination Temp: 21 degrees.
Germination Time: 6 to 9 days.

Plant out in mid June in the polytunnel when all risk of frost has passed. They will need to be potted on to progressively larger pots until ready to plant, always protecting from cold.

Onions

Sow: in February for maincrop onions. Early is good because the more growth that you can get down before the summer solstice, the larger your harvest will be.
February to late May for spring onions. You can continue to sow up to late July for overwintering and spring harvests.

Onion sets are planted after the spring equinox (20th March) to reduce chances of onions bolting.

Germination Temp: 18 - 20˚C
Germination Time: 5-10 days

Parsnip

Sow: directly in garden soil in mid to late March.

It's important to have moisture around the seeds for the first 14 days when germinating. This isn't usually a problem with early sowing, but drills may need to be watered in dry weather.

Germination Temp: 10˚C +
Germination Time: 15-21 days

Peas

Sow: February indoors; March outside.

Starting early is good to get as much growth as possible before peas start to flower. Overall growth slows or stops altogether once flowering starts.

Germination Temp: 10˚C + but quicker if warmer (18˚C ideal).
Germination Time: 6-10 days

It can be handy to sow 3 seeds in a Huw Richards module trays and then plant out in groups of 3. Transplant 2-3 weeks after sowing under fleece for protection.

Potatoes

Sow: Plant mid to late March depending on weather (e.g. if the soil is too wet). Plant up to the second week in April for maincrop varieties.

Sprouting Temp: 10˚C+
Time: 15-25 days.

Ideally seed potato tubers should be the size of large egg; larger ones can be halved. If on the other hand seed potatoes are too small, the harvest will be lesser as it takes longer for plants to establish.

Always have fleece on hand to protect potato shoots from frost that can occur well into June.

Radish

Sow: late winter or early spring; or again in late summer/early autumn.

Germination Temp: 18˚C
Germination Time: 2-4 days

It's easiest/quickest to multisow 5 seeds per cell, thin to 4 and then plant out in a group.

Spinach

Sow: in February for spring crops - no later or they will bolt. Sow in late summer for autumn harvests (with no risk of bolting).

Sow 3 seeds per module, aiming for 2 plants from each.

Germination Temp: 18˚C
Germination Time: 5-8 days

Winter Squash

Sow: mid April

Temp: 20˚C
Time: 4-7 days

Sow in Huw Richards trays, and pot on after 3 weeks if it's too cold to plant outside.

I grow in the polytunnel for better yields, but they are a very large plant so only do this if you have the room. Winter squash also grow very well outside.

Swede

Sow: Early sowings will bolt; instead hold off until mid May for the best autumn/winter harvests.

Germination Temp: 18˚C
Germination Time: 3-5 days

I sow in small trays and prick out into Huw Richards modules to grow a larger plant; turnip and swede seedlings are vulnerable to flea beetle and other pests so I want a decent size plant to plant outside.

Turnip

Sow: Unless sown very early, turnip will bolt if sown before late summer. It's much more successful as an autumn crop.

Multisow 4-5 seeds per module and thin to 4; turnip grows very well planted out in groups.

Temp: 18˚C
Time: 3-5 days

Sweetcorn

Sow: April - May under cover. You can sow outside in mid May, but mice love the seeds so it's better to sow in modular trays.

I grow sweetcorn in the polytunnel, so sow in mid March for an earlier harvest - which works very well. Only about 75% of sweetcorn seeds germinate, and some don’t produce great seedlings - so I would always sow double the amount you want and pick the best.

Temp: 20˚C
Time: 4-7 days

Tomato

Sow: Mid March is the best sowing time for tomatoes, with good daylight hours.

Tomatoes need warmth to germinate, but the temperature can be significantly cooler for seedling growth - ideally as cool as possible down to around 14˚C but no lower than this.

If growing in a polytunnel or greenhouse, plants need to be protected from frost at night. A heat mat is preferable but a double layer of fleece can also be enough if not too cold, tomatoes are tougher than other warm climate crops.

Temp: 20-25˚C
Time: 4 - 7 days