This year I’m growing tomatoes, bell peppers, zucchini and bush beans in containers. I’m aware of minimum container size requirements for each, just wondering what ratios of medium are best. Here is what I have for a single container:
20% Revitalized Old Potting Mix (with a wetting agent added)
30% New Miracle-Grow Ready-Made Potting Mix
35% Aged Compost or Aged Manure (or a 50/50 combination of both)
15% Perlite
I also have 1 year old leaf mold on hand if you think that would be necessary for improved soil structure.
Is there anything else I should add?
Feedback is appreciated
Thanks
Good for you to be growing vegetables in containers. Even though I have a series of raised garden beds, I still add containers.
We have an excellent guide to container gardening that you might like to check out. In it, you will see some detailed advice about making your own potting mix.
With respect to your specific questions, I’ll address the re-use of last year’s mix, first. Here’s a response we provided to an earlier inquirer. You will notice that we don’t recommend using more than 50% of re-used soil and only if there were no diseases or pests in last year’s containers.
With respect to the additional ingredients you mention, I would caution you about the use of the kinds of potting mixes that contain crystals intended to retain water; with rain and watering, there is a risk of the soil taking so long to dry out that the plants get root rot. With climate change, we are experience more, heavier, longer rainstorms. As for wetting agents, many people are uncomfortable with the chemical compositions. You’ll find them discussed in this detailed article from the University of Massachusetts.
As for manure / compost, since the potting mixes already contain some, be careful not to add too much. Composted manure tends to be high in phosphorus and calcium and, used in excess, can inhibit the uptake of other nutrients, resulting in deficiencies, even though you added it in the interest of nutrition!
35% manure might be a bit much and 50% will definitely be overkill. I would suggest between 20 and 30% depending on the nature of the vegetables being grown. Tomatoes, peppers and zucchini are heavy feeders, so will appreciate the manure. When calculating the percentage to use, don’t forget that if you added manure to last year’s containers, your re-used mix will include some!
Commercial potting mixes all contain perlite or vermiculite, with the intent of loosening or lightening the mix. I expect that you suggest adding some because your re-used mix will have compacted, so that’s a good idea. You could certainly use your leaf mould, as well.
As I mentioned, I do grow vegetables in containers, filling them with 75% ProMix and 25% composted manure. I do replant after harvesting some plants, so add a fish-based fertilizers when planting the second crop. Long growing vegetables may need a boost mid-season as well, since every time you water your containers, some nutrients are leached away. Here’s an article from the University of Vermont on fertilizing vegetables mid-season.
Enjoy your container gardening and the resulting produce!