Here's a close-up of the lawn in a patch that's growing quite well

Here's a closeup of a bare patch, with tiny plants growing in it

Another photo of a bare patch

Spring is not the time to seed. If you seed now, you will bring up all the summer weed seeds. Crabgrass is the big one here, and I'm sure, there, too. When you do seed, the idea is to make the turf more dense with grass plants. Your rye and fescue grass grows as individual plants. A grass like Kentucky bluegrass spreads out and fills in thin areas. That might be worth overseeding for you next fall, but it only grows in full sun. If you have half a day of shade, it won't work great for you. KBG also goes dormant in the winter. Depending on where you are in NZ, it might remain green all year.

You can soften your hard soil with shampoo. Any clear shampoo will do. I like generic baby shampoo from Walmart. Shampoo is a surfactant which will penetrate the soil and allow water to penetrate much deeper. If you apply at a rate of 10 cc per 10 square meters, then water it deeply with 3 cm of water, and repeat that in 2 weeks (do you have metric calendars?), your soil should be significantly softer when you irrigate. You don't have to worry about using too much shampoo. One of the gurus on another forum tried it using 20 cc per square meter every week and had no problems. But 10cc is enough. Anyway shampoo works by moderating the soil moisture. It creates a soil environment which is great for the beneficial fungi your soil needs. Once those fungi have repopulated the soil, it will become soft when moist and hard again when dry. The two shampoo treatments have lasted me since 2011. Once you try the shampoo, you'll forget all about core aeration. Core aeration is a way for landscapers to make their boat payments. You can buy expensive surfactants designed for golf courses, but shampoo works very well.

Don't use clay breaker unless you have a soil test which recommends it. NZ/AU might have good soil tests but I know that Logan Labs in Ohio has a great one for $20. Of course let them know where you live and what you're growing.

Find a feed store that sells alfalfa pellets (rabbit chow). It should come in plain, 20-kilo bags. Apply at a rate of 10 kilos per 100 square meters. Moisten the pellets after you apply so they will swell up and burst. Then rake them into the soil or simply drag a hose across them so they fall down to the soil. Give that 3 full weeks to work. You can repeat that as often as you can afford. And I would suggest you use it now and in a month just get started. That same guru tried overdosing his lawn with organic ferts and could not do that, either. 10 kilos per 100 is a start, but you could go to 80 kilos per 100 before smothering the lawn with too much love. It's up to your budget. The alfalfa should green up the lawn and get it growing. If all you have is rye grass, that's all the alfalfa will do. In order to improve the density, you'll have to wait until next fall.

You should be watering about 3 cm, once per month this time of year. Here's a chart for you. It is based on daily high temperatures.

Above 35 degrees C ==> water 3 cm once per week
25 to 35 ==> once every 2 weeks
20 to 25 ==> once every 3 weeks
Less than 20 ==> once per month

Of course Mother Nature will help you out sometimes so you won't need to water the full amount every time.

I forgot to mention how to measure 3 cm for your watering. We have cat food and tuna cans which are about 3 cm tall. Put several of those out in the lawn and turn on your sprinkler or sprinkler system. Measure how long it takes to fill all the cans. That is the time you're looking for to get 3 cm.

Thanks for those tips, very helpful! I'll get some of that alfalfa and give it a go. Nice easy tip on watering volumes and baby shampoo too.

Curious why seeding at the start of spring isn't helpful? There are a lot of empty patches, I've laid seed in the spring before and it grew fine. The cost of seed isn't an issue, if I lay some in spring and it doesn't take I'll just lay more in Autumn anyway.

Any idea what those tiny plants are growing in the bare patches? They're often only 2-5mm high. I'd probably give the lawn empty patches a bit of a rake to try to disturb the surface before I lay and seed, plus that would get rid of some of the leaves.

Thanks again for the tips :)

The problem with Spring seedings is twofold --(1) the Summer heat comes quickly and is tougher on young grass than winter cold, and (2) the watering needed to properly germinate grasses is also the perfect conditions for weed growth, exactly when weeds are ready to germinate -- and you can't then use many weedkillers because of the seedlings.

It looks like your "tiny plants" are probably in the moss family. The slimy blue/green stuff underneath them is most likely Cyanobacteria, which is also called "blue/green algae" although it is not an algae.

Should I treat the lawn with something to get rid of the algee, moss, or fugus type stuff growing there?

Should I treat the lawn with something to get rid of the algee, moss, or fugus type stuff growing there?

Should I treat the lawn with something to get rid of the algee, moss, or fugus type stuff growing there?

Should I treat the lawn with something to get rid of the algee, moss, or fugus type stuff growing there?

Should I treat the lawn with something to get rid of the algee, moss, or fugus type stuff growing there?

Should I treat the lawn with something to get rid of the algee, moss, or fugus type stuff growing there?

Should I treat the lawn with something to get rid of the algee, moss, or fugus type stuff growing there?

The shampoo, infrequent watering, and your normal organic fertilizer should help.

Sorry for the repeated message, not sure what happened there. I'll try the suggestions, thank you for your help.

Please let us know how it comes out. We rarely get international posts here.