Timetable for growing tomatoes: a summary of a decade of learning I started growing tomatoes in the wet summer of 2009 and was quite frankly, not very successful. It probably took me until 2013 to know what I was doing, when I had a breakthrough season, benefiting greatly from a hot, sunny July and a Shirley plant which yielded well over 100 tomatoes grown in a pot out of doors. It was then that I realised that formulaic advice was just that and that personal experience should always trump generic advice lacking context. Since 2013 I have worked on understanding the holistic life cycle of a tomato from seed to composting the haulms in the autumn, trying to align any interventions to the needs of the plant as it grows. I evaluated around a dozen strains of tomato for suitability for growing in pots outdoors and have also grown about six in soil, identifying two or three well suited to that here in NW London.
I have learned to save good tomato seeds and they routinely germinate now within 3-6 days of sowing. Particularly good years for saving like 2014 are still germinating and growing beautifully six years on. I have won plenty of prizes for tomatoes at local shows but showing tomatoes is different to growing for eating: I grow separate strains for showing and use a Quadgrow to ensure perfect conditions throughout the summer. The majority of plants I grow for eating are mainly grown in 30cm pots and live on an outdoor patio, with a covered carport available to protect them when the rains come. As my garden’s soil has improved through five years of no-dig organic/biodynamic gardening, I have found that tomato crops can be harvested from the soil too. From Seed to Final pot/garden position: working backwards to decide when to sow. I have found in NW London that, in general, it is safe to leave tomatoes outdoors permanently from around 21st May. Of course, some years this can be earlier, but for me, the 30cm pot size is when it becomes impossible to bring the tomatoes indoors at night if cold intervenes, so I do not want them potted up too early into their final homes. 15cm pots can happily live indoors overnight, so even if they go out to enjoy spring sunshine and harden off during the day, they are still usually pampered at night. Having decided I want to do final potting up around 21st May (give or take), I have noticed that plants do not want to stay in 15cm pots for more than 17 days (preferably 14 days), since if they do, they start growing vertically too soon. So I don't really want to be potting up into 15cm pots before May 1st in ideal circumstances. I have also found that 10 day old seedlings transplanted into 8cm pots are ready to be potted on after 3-4 weeks. It varies from year to year, depending how sunny and warm April is (in 2019, we had a week of hot summer sunshine in April and my tomato plants were propelled forward with rocket fuel: I potted on my prize tomatoes to 15cm pots on day 19, a record I doubt I will ever surpass). So transplanting seedlings into 8cm pots from around 8-14th April sounds realistic. Finally, I have found that germinating seeds well means that plants are through between day 3 and day 7 in the main. If they are not, either your seeds are duff or you have not given them a good burst of heat above 20C. So the seeds are ready to transplant into 8cm pots from around day 6 - 10. Based on that a sowing date in the last week of March to the first week of April has proven to be the best for me. The effects of earlier or latter sowing dates Of course, tomatoes can be sown earlier or later for specific reasons. Here are three reasons I may choose different sowing dates for a few plants:
- Showing tomatoes in late July - to do this a sowing date in early March is preferable, giving 18-20 weeks of growing time before harvesting show tomatoes in late July;
- Harvesting a June/early July crop - the strains Red Alert and Maskotka are both hardy strains capable of being sown early and harvested early. My record early harvest date for a tomato is June 9th using Maskotka plants and Red Alerts grown in pots will regularly harvest in early July;
- Showing tomatoes in mid September to early October is best achieved using a sowing date of very early May - that way, the plants are only around 20-23 weeks old when show time arrives.