Planting Seeds: Inside or Outside?

Read time: 4 mins

If you want to plant your own seeds instead of buying seedlings or transplanting, then you can either sow seeds directly into their final growing position, or start them in seed trays or pots, and later transplant them to their final growing position. Some plants you can only really sow the seeds inside, some plants you can only really sow the seeds outside, and some plants you have more of a choice. I say seeds here because most are grown from seeds, but I'm also including potatoes, onions, and garlic, which are grown from the thing itself.

Squashes planted inside in newspaper cups

Why sow seeds inside?

Some plants need to be started early enough that in most places it's going to be too cold to plant them outside. It's recommended to plant these inside to get the most out of the growing season. If you wait to sow them outside then they'll have a shorter growing period and they may not be ready to harvest before the end of the season, or you may get less, smaller or unripe fruit from them.

Quicker plant growth. You can control the light and temperature that they are getting, making it warm enough for them to grow well and extra light than they would be getting outside in winter and spring. This can give your plants a headstart, leading to bigger and/or stronger plants, as well as more fruit.

Reduce the damage from pests. Having plants inside removes most of the pests that may attack a young plant, like slugs, snails and birds. You may still get flies or aphids, but usually less pests than outside. Seeds sown outside can be protected, as can outdoor seedlings, but this won't always work and planting inside removes that from the equation.

You have a mulch outside, which can prevent seeds from sprouting, unless you remove it.

Why sow seeds directly outside?

You don't want to disturb the roots. Plants generally don't like their roots being disturbed, but if you are careful (taking the entire pot or modules worth of soil or compost out with the plants) then many plants don't mind being transplanted. However, crops where the roots are the main part of the crop (potatoes, carrots, etc.) do not like being transplanted. 

The temperature has warmed up by the time the seeds want sowing. This is going to be most of the plants that were traditionally grown in the UK.

You have a way of protecting the young plants from the cold and frosts. Greenhouses, polytunnels, cold frames or fleeces can be used to keep them warm enough during the still cold spring.

You want to plant seeds the easier and quicker way. Needing to only plant once instead of double plant (sowing seeds inside and then planting the seedlings outside).

You don't have the equipment, or don't want to get the equipment needed for planting seeds inside. Speaking of which, what equipment do you need?

A young mustard plant sown directly outside

What do you need to start seeds indoors?

Grow lights

Plants need light, and even southern facing windowsills don't really give seeds enough light. You could get by, but the plant growth won't be as good. A greenhouse or glass conservatory would provide enough light and be good enough, but grow lights would still provide more light.

Heated mat or propagator

Lots of seeds want to be warm to germinate, often between 20 and 30 degrees. The seedlings ideally want to stay above 10 degrees. Heat mats and heated propagators usually increase the temperature of a room by 10 degrees, so if you don't have somewhere that will be those temperatures, then heat mats or propagators may help you.

Trays or pots

Modular trays or individual pots are most commonly used for growing seeds inside, due to the ability to plant them out while minimally disturbing the roots. You may sometimes 'pot up', and move a plant into a bigger pot as they get too big for their current pot to prevent them getting rootbound. They can be bought from any garden centre and should be available in every shop that sells some garden things. Or you can use newspaper, like I sometimes do, with a paper pot maker. Tear strips of newpaper and roll them up, making small pots.

Compost

Use a light compost so that the seedlings can push through when they emerge. Compost should provide enough nutrients in that small pot for the seedlings until you plant them out to their final growing position.

Which to choose?

I'm going to go through all of the plants from Plants to Grow for Beginners, and put them into categories. Plants you should start inside, those to start outside, and those that can be started either way. I will go into more detail in the individual beginner plant posts coming up.

Inside

Tomatoes, cucumber, courgette, winter squash. These can be started outside if you want to, but it's recommended to start them indoors. Basil and coriander fit into this category from the herbs.

Outside

Potatoes, radish, garlic, onion, carrots, parsnip, beetroot. These really need to be started outside as they won't like to be transplanted, and with the potatoes, garlic and possibly onions, you'll be planting something quite big anyway, so may not even have the space inside. Most flowers and herbs can be planted inside, but it's unnecessary and won't really benefit them, so can be planted outside. 

Either

Peas, broad beans, runner beans, kale, cabbage, lettuce, spinach. These plants can do well sown either inside or outside, and it's really personal preference which you do.

I prioritise those that do best from being planted inside, and try to plant enough of those inside for how many I want to grow (grow some extras in case they don't come up or don't survive), and then see how much space I have left for those that can be planted either. Also combined with the timings of when they will be growing. I'll go into more depth in the individual posts for how important it is for each beginner plant, and then in the future when I include other plants I'll do the same for those.

I am proud to be affiliated with JustSeed, a company that I have bought seeds from for a few years now. I believe in what they are doing over there, and if you are going to buy seeds, garden tools, or seedlings, then please consider checking them out and using my link below to do so. Thank you for supporting me.

https://justseed.com/?ref=ANGJ