Q. Does anyone have plans for mini-greenhouses that you can build and start seed in to about 3-4 feet tall?
A. We have plans for greenhouses available free on the Foundation website.
The plans for the recommended Mittleider-style greenhouse, with a “continuous ventilator” running along the peak of the roof, are available for the asking, just by sending me an email at firstname.lastname@example.org. The pictorial description of building the greenhouse is included in the free downloadable chapter in the Books section of the website at https://foodforeveryone.org/grow_bed_gardening/, next to the Grow-Bed Gardening book.
And plans and explanation for a smaller, quonset hut-shaped structure are included in the free down-loadable chapter from the book Grow-Box Gardens.
All seven books have an important chapter included for your inspection and study, and we invite you to avail yourselves of the opportunity to learn all you can in this way.
The question is asked if a person can grow his plants to 3 or 4 feet tall in one of these greenhouses (and then presumably take them out to the garden), and I would counsel against it. By the time your plants are about 12″ tall their roots are crowding a one-gallon pot, and the stems are susceptible to falling over, plus they take quite a bit of space for proper light. If you are going to have them in the garden you should time the planting of the seeds to be no more than 12 weeks before that final transplant time. the plants will be about 12″ tall, with strong stocky stems, if you have pruned and cared for them properly.
On the other hand, if you want to grow tomatoes, cucumbers, peppers, etc. throughout the growing season in the greenhouse, they should be transplanted into the final bed location by the time they are 8-12″ tall. And they should be at or near ground level, rather than on tables at that point, in order to give them plenty of height to grow more than 7′ tall.