What would be the easiest way to ensure the soil is bug free especially if using for seeds? 

If you are seeding in native soil, you may want to consider soil borne pathogens as well as insect pests and nematodes that can infect and infest seeds and seedlings.  I don't think its practical to try and "sterilize" the soil. There are beneficial organisms that you would be killing off too. 

 

I don't know what your project is, what kind of seeds or scope of garden area you want to seed, but guessing that you want to plant a small garden area and not a field crop, I would suggest that you prepare some flats with an artificial growing medium (potting soil), that is essentially pest and disease free. Start your seeds and then when germinated, transplant up to 2" or 4" pots until the seedlings are hardened off and more resistant to pests and disease when you plant them out into native soil. Using high quality seeds for plant varieties that are proven resistant to local pest and disease issues is a key part of intelligent plant management. 

 

Of course the best program is while your seeds are germinating, to prepare your soil well with mineral and biological amendments.  The improved soil will be better for plant resistance to pests and diseases.  

 

You may be interested in the book: How to Grow More Vegetables by John Jeavons.  It outlines the very comprehensive Biointensive approach to preparing your garden, starting plants and ongoing management. 

Sorry should have been clearer.

Really meant for soil in pots indoors to start seeds growing.

A few different veggies herbs etc. Once started then move to outside.

Worst 'bug' is I've heard it called 'cut bug' . The seedlings start to grow then get chopped at ground level and die.

Thought about baking the soil for a while over 100 degrees should kill off any small bugs or bug eggs.

As I learnt it 40 years ago, you could sterilise soil and compost by either steam treatment or chemically. Steam involved heavy tarpaulins and a steam producer, took days. https://en.wikipedia.org/wiki/Soil_steam_sterilization

Chemically we used Basamid, nasty stuff which also wasn't easy to use and required a germination test at the end of the period to be sure the chemical was decomposed. I only used this with seeds that were expensive and on a small scale. There are other chemicals.

Heating up to 100 °C would most likely kill most bugs. but how were you planning to do this? Boiling water poured over the soil won't work.beyong the first few centimetres.

 

Then there is solarisation, which you might want to look at, I know for as fact that the villagers around here used to dig their soil over very roughly and leave it exposed to the sun when they were having problems with soil borns, not sure how well this worked, but you can find instructions on the net, written by people that live in temperate climates.

Wood vinegar is supposed to kill bugs but it didn't kill the ones I wanted to get rid of when I tried it.

I wouldn't worry too much about the fact that all organic life in the soil will be destroyed, this returns very quickly including the bugs unless very large areas have been treated. 

 

I just grow what I know will grow and try to refrain from using chemicals. Some people have gone for aquaponics or growing bags.

17 minutes ago, cooked said:

As I learnt it 40 years ago, you could sterilise soil and compost by either steam treatment or chemically. Steam involved heavy tarpaulins and a steam producer, took days. https://en.wikipedia.org/wiki/Soil_steam_sterilization

Chemically we used Basamid, nasty stuff which also wasn't easy to use and required a germination test at the end of the period to be sure the chemical was decomposed. I only used this with seeds that were expensive and on a small scale. There are other chemicals.

Heating up to 100 °C would most likely kill most bugs. but how were you planning to do this? Boiling water poured over the soil won't work.beyong the first few centimetres.

 

Then there is solarisation, which you might want to look at, I know for as fact that the villagers around here used to dig their soil over very roughly and leave it exposed to the sun when they were having problems with soil borns, not sure how well this worked, but you can find instructions on the net, written by people that live in temperate climates.

Wood vinegar is supposed to kill bugs but it didn't kill the ones I wanted to get rid of when I tried it.

I wouldn't worry too much about the fact that all organic life in the soil will be destroyed, this returns very quickly including the bugs unless very large areas have been treated. 

 

I just grow what I know will grow and try to refrain from using chemicals. Some people have gone for aquaponics or growing bags.

Was having problems with rosemary starting well then just stagnating. Someone suggested watering once a week with 50/50 milk and water and it works. ?

Just now, overherebc said:

Was having problems with rosemary starting well then just stagnating. Someone suggested watering once a week with 50/50 milk and water and it works. ?

That's interesting. Our neighbour pours soured milk onto his plants. 

My rosemary cuttings usually start quite well but keeping a balance with watering is difficult, have lost a few due to root rot, others to putting them out in the sun and forgetting go water. I use bought in potting compost for them.

44 minutes ago, cooked said:

That's interesting. Our neighbour pours soured milk onto his plants. 

My rosemary cuttings usually start quite well but keeping a balance with watering is difficult, have lost a few due to root rot, others to putting them out in the sun and forgetting go water. I use bought in potting compost for them.

Rosemary doesn't like sun here. We have ours where they get sun first thing in the morning then shade all day after.

Seems to work.