Indoor Tomato Sowing Mistakes To Avoid!

Sowing tomato seeds indoors is the best way to sow them; you can get a good headstart on the year and make great strides towards a bumper harvest.

But as with all things gardening, there are some mistakes you need to avoid, let me help you out!

Understanding Last Frost Dates

You don't want to start tomatoes too early unless you have the room to grow them pretty large indoors. It's ideal to begin 6-8 weeks before the average last frost date of your area.

For me, this is May, which means a sowing date of mid to late March, although I often go a little earlier. But I do have a good indoor setup with grow lights where I can grow my tomatoes quite large before moving them to the greenhouse.

If you sow too early, then you will either have massive plants cramped in your house, or you will have to move them to the greenhouse too early and risk them being killed by an untimely frost.

Sowing On Windowsills

Sowing your tomato seeds on windowsills is a very common way of growing them, but unless you have the perfect south-facing window, then they often won't get enough light.

A much better way is to set up a little seed starting station with grow lights so you can ensure your young plants don't grow leggy!

Using Sterile Potting Mix

When sowing indoors I advise you to use a sterile compost for starting your seeds. If you don't do this, then you will have to get used to having plenty of fungus gnats flying around your plants!

I use coco coir compost, which is sterilised, but another method is to take your regular compost and microwave it - killing any fungus gnat eggs that might be in the soil.

Moistening Soil Before Planting

Seeds need water to germinate - everyone knows that. But watering them after planting can often wash the seeds about and sometimes wash them straight out of the pots or into a neighbouring cell! This can wreak havoc with your labelling system.

So what I do is pre-moisten the compost so I don't need to water it after I have put the seeds in.

Another option is to use a tray and water into the tray rather than watering the soil. The compost will soak the water up from the bottom without moving your seeds.

Seed Depth and Spacing

Tomato seeds should be buried about 3-5 mm deep in the soil. They should be spaced sufficiently to allow for adequate air circulation and growth, typically around 2.5 cm apart within the same tray.

Avoiding Overwatering

Overwatering can lead to diseases such as damping-off. This will cause the roots of your seedlings to die, and your plants will wilt before dying off completely.

Ensure you have drainage holes in the bottom of the container you are growing your seedlings in.

Only water when the top 1cm of soil has properly dried out; this will ensure you don't overwater but also don't underwater them. It is a delicate balancing act.

Hardening Off Seedlings

Before transplanting outdoors, tomato seedlings need to be acclimatised to outdoor conditions. This process, known as hardening off, involves gradually exposing seedlings to outdoor conditions over a week or more.

Timing Your Transplant

Transplanting should be timed so that seedlings go out after the risk of frost has passed and when nighttime temperatures consistently stay above 5°C.

Seedlings should also be well-established plants that are capable of dealing with cooler conditions.