By September, kale and spring cabbage seedlings planted out a few weeks ago should be about 15cm tall and rooting into a bed that is starting to cool and dry out unevenly. A straw mulch laid now keeps the soil temperature steadier, holds moisture between waterings, and smothers the weed seedlings that would otherwise compete through autumn. It's a job done once per row that keeps working until spring.

Mulch Kale and Spring Cabbage Transplants with Straw for Winter

What you need

1 bale straw sold as mulch or animal bedding, not meadow hay, and from a known source
3 buckets garden compost or well-rotted manure, per 3m of row

Step by step

Hoe off any weed seedlings that have come up between the plants and firm the soil back down. Mulch smothers weeds that haven't germinated yet, but does nothing for ones already up.
10 min
Water the bed well if the soil is dry. Mulch keeps moisture in or out, not up, so start from where you want to be.
5 min
Fork the compost onto the surface around each plant and work it lightly into the top few centimetres of soil without disturbing the roots.
15 min
Spread straw 5-8cm deep along the row, banking it up around each stem but leaving a clear 5cm gap right at the base.
20 min
Firm the straw down with the back of the rake so wind doesn't lift it, and tuck the outer edge under itself along both sides of the row.
10 min
Check a handful of the straw for slugs before you finish and clear any you find, since you've just built them a shelter next to dinner.
5 min

Afterwards

Check the mulch after heavy rain or wind and top it back up where it has washed thin, especially at the row ends. Pull it back from any stem that looks pale or slimy at the base, which is early collar rot, and let that spot dry out before re-covering. By late winter the straw will have flattened and started to rot down; leave it in place as soil improver rather than raking it off.

Questions

Can I use hay instead of straw?

Hay carries far more weed and grass seed than straw and mats down into a slimy layer faster, so it does both jobs the mulch is meant to do less well.

Won't the mulch make slugs worse?

Straw does give slugs cover, but going into a cooling, drying autumn the moisture and frost protection is usually worth the trade-off. Check under it every week or two while it's still mild.

What if I can't get straw?

Shredded autumn leaves or spent hop waste do a similar job, though they mat down flatter and need topping up more often.

How long does the mulch last?

A 5-8cm layer usually holds through to early spring before it has rotted down enough to need forking in or replacing.