*UPDATE* I've discovered 'Laundry Sheets' so I am writing about those. My thoughts on powder (rather than liquid/tabs -in-plastic) is still below for you to look at, if laundry sheets work out to be too expensive for you.
You will have seen a few different brands of 'laundry sheets' advertised. Laundry sheets are brilliant. They save so much space and they reduce the carbon footprint of 'doing the laundry' as they are so light to transport (especially compared to laundry liquid).
After much research (you know me!) I settled on the 'Simply Living Eco' laundry sheets as the company is a family-run business in Yorkshire (north-east England) and the sheets themselves are made in the UK.
I pay around £8 for 32 sheets via a monthly subscription deal (I rip them in half to make the packet last longer - this works for me as I also put in 2tbsp of Napisan to sanitise the laundry items at 40 C) - I write more about this in my 52HOME blog... So, I haven't really tested out the stain-busting abilities of these sheets, as Napisan does that. So if you don't use Napisan in your wash, it might be a good idea to get a sample size pack of laundry sheets to try before committing to a whole month's worth.
I buy my laundry sheets straight from the Simply Living Eco website, but they are also stocked by the mighty Welsh eco website Babi Pur.
The Simply Living Eco laundry sheets arrive through the letterbox in a plastic bag (sadly) but at least this bag can be recycled at many supermarkets. Plus a thin cardboard sleeve inside. These laundry sheets contain only 4 ingredients (well the fragrance free ones anyway) and they are palm oil free, not tested on animals and vegan.
Another option is refilling your existing product bottle with an eco version of laundry liquid, from a refill shop. If getting to a zero-waste refill station is convenient (not requiring a special journey out of your way) then once you existing laundry liquid bottle is empty, rinse it well and take it along to be refilled. The refill brand SESI operates an awesome 'closed loop' recycling system for the plastic drums it sends out to refill shops, i.e. it takes back and reuses all of the 5L and 20L containers numerous times, so try to find that brand if you can.
Or, if the laundry sheets / refill liquid options are too expensive, you could still switch from single-use plastic bottles of laundry liquid / single-use plastic boxes of washing tabs to buying washing powder in bulk from your supermarket.
You can bulk-buy washing powder in a large box from the supermarket, Tesco sells Fairy Non Bio Powder in a 4kg cardboard box for about £10. I use far less powder per-wash than is suggested, making the box last even longer. I do add 2 tbsp of Napisan to each wash though (to sanitise the laundry items at 40 C) - I write more about this in my 52HOME blog...
Before I discovered laundry tabs, I chose the box of Fairy as; the cardboard box is enormous (so energy is saved making just one box rather than many), I have the space to store it in a large airtight container, it comes from a store that I shop at anyway (meaning no special wasteful trips), the fragrance is minimal if you don't use too much (I find most laundry products far too scented) and it isn't overly expensive (especially if you use less per wash than suggested).
If you do buy washing powder in a box (having previously used liquid detergent or capsules) you will need to think about storage. If you leave the powder in the box it will clump together (due to moisture in the air) by the time you get to the bottom of the box (or sooner if you buy a huge box!) I keep my washing powder in this 11 litre lidded box from Amazon, which was well worth the £10 price-tag. *Update* - the 11 litre box no longer holds laundry powder in our house, it now holds 3kg of guinea pig-food nuggets, so it is still being put to good use!
I found this an easy 'green' switch to make, I hope you do too.