Why are my vegetables not growing well in the elevated planter I created?


I created an elevated vegetable planter in a metal trough on legs. I lined it with black landscape cloth. The bottom of the trough has many circular punched out holes for drainage. I put in a mixture of purchased Coast of Maine container (2 parts) and Coast of Maine lobster compost (1 part). I planted radishes, cilantro, celery, leaf lettuce, arugula, spinach, beets, and carrots. Most all came up well but they then are stunted, get stressed and flower, get spindly. I called the Coast of Maine and they felt the mixture I used was fine. I water almost every day and soak it. It is in sun about 6 hours a day. Could it be that the potting mix is getting too hot, the temperature not being mitigated by contact with the earth? Any other ideas? No pests apparent and some plants look good they just stop growing while others flower and don’t produce the crop we expect. 


Rebecca Long, Sustainable Agriculture and Horticulture Professional

Thanks for reaching out! It sounds like your plants are either getting leggy or bolting (or possibly both). Leggy plants can be the result of not enough light or crowding. I suspect crowding may be the issue for some. You can sow them thickly to ensure good germination but you’ll want to thin them to make sure they have enough room to fully develop. For instance radishes need to be thinned to up to 3″ apart (depending on variety) in rows 12″ apart. Good spacing also helps with airflow which cuts down on foliar diseases.

This time of year it is also common to see cool season spring crops begin to bolt (start growing vertically to flower and set seed). Different plants have different triggers for what makes them “bolt” including temperature and day length. For these crops you can pull them now and plan to do another round in fall, and consider planting them earlier next year. Cilantro in particular is quick to bolt (especially if transplanted, direct sowing is ideal) so it’s best to plant multiple successions if you want a continuous supply of leaves.

My last thought is that the mix you used may have been a little heavy on compost (we usually recommend no more than 25 – 30% organic matter. Since the container mix you used also contains a lot of organic matter you are likely beyond that. If those compost is releasing enough nitrogen, that could also be resulting in leggy growth with plants focusing more energy on leaf growth (which could explain your rootless radishes as well). I wouldn’t add anything further this year but if you see it being to subside, consider adding something with less organic matter going forward.