I have had great success with phacelia - bee plant, just cut it down when you're ready to plant the next thing. Good idea to mix it with rye, vetch... mix lots of things that will still germinate when you are ready to seed. Bringing insects to your garden will make it so interesting for the kids. Make sure to seed as soon as the soil is put down.
My cheap and easy way of building soil and clearing it for planting is to plant potatoes by dropping them onto the soil, then cover each with a spadeful of
compost or soil and mulch thickly with all the weeds/dead plants I can find. Pull off the mulch to treadure hunt for potatoes and the ground is lovely and ready to plant. Bonus, the decomposing plant matter attracts lots of creepy-crawlies, make sure the class have magnifying glasses and jam jard handy. In my climate, we can plant the potatoes before the easter holidays and dig them either as earlies before the summer holidays or get whoppers when school starts again in autumn.
Snacking plants are a great favourite with the kids - strawberries, peas, rasberries, anything that can be eaten straight off the plant.
Teach them to mulch, it will make your good soil better, less watering and weeding! We have slugs in spring, so we mulch like mad June-November and then let it all rot away until spring. We get grass clippings and leaves. Teaches the kids about not dropping their sweet wrappers.
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