Potted Plants Need To Be Planted

Black-eyed Susan Seedlings January 30 2019

Potted Seedlings 8/3/2019

Same-aged seedlings planted 3 weeks previous to above

As a gardener, we sometimes wait for just the right time to plant. I've done it lots of times in the past, but in general, the best time to plant a potted specimen is right now. Plants respond to real soil in a way they simply can't in a potting mix. Forget trying to match things up by fertilizing. It is not the same. It is true that most, if not all, potting mixes are short on fertilizer, but it is not a lack of fertility that causes the types of results pictured above with my black-eyed susans (Rudbeckia hirta). I have fertilized the nursery plants, but none of them show the same type of growth that the ones have in my landscape after about 3 weeks. As you can see, their foliage is much denser and they are sending up flower stalks. That is not the case with my nursery plants, though they are healthy with good root systems......... at least they look good.
Soil is much more than fertility. Many gardeners do not fully grasp that which is why I wrote my last book - The Nature of Plants: An Introduction to How Plants Work - and devoted a chapter to soil. Here in Florida, and as a transplant from the Midwest, I understand all those who move here and think that they must amend their sandy soil to get their plants to thrive. We equate sand with fertility. Of course, that is simply wrong. Fertility has nothing to do with soil-grain size and sands can have plenty of fertility. Florida has one of the richest diversities of native plants anywhere in North America and that happens in mostly sandy soils.
Fertility is only one edge of the coin. Equally important is the soil health and that equates to all of the living components found in healthy soil. Plant roots do a generally lousy job of pulling in water and its dissolved nutrients by themselves which is why they seek out soil microorganisms to assist them. Of special importance are the group of fungi known as glomeromycetes - the mycorrhizal fungi. Mychorrizal fungi form mutualistic relationships with plant roots that then enable roots to become super efficient at water absorption - and thus, nutrient absorption as well.  One of the first things a developing root does on emergence is to send signals out through the soil to attract the right mycorrhizae.  This must be a very frustrating thing for plants in pots as the vast majority of potting mixes are sterile. Plants in pots have to rely solely on their own root systems for water and nutrients. The relationships they need to thrive will only occur in living soil.
Soil also contains other microorganisms that improve a plant's health. Though we often think of bacteria and nematodes as destructive creatures, the vast majority are important to plants. They too are only found in healthy soil. As you look and compare the above photos of my black-eyed susans, it is easy to see the difference made by planting into healthy soil. This same story is repeated dozens of times in my new wildflower garden (though it's true for all plants). I have "rescued" dozens of tiny seedlings from my nursery that were destined to die by sticking them into my landscape before they succumbed. Some of these are simply species that "hate" pot culture, but it's true for every plant I've added. Many of them would be dead today if I hadn't have planted them out. It's not the fertility, it's the microorganisms.
I grow most of my plants from seed. I enjoy the whole experience of watching seeds sprout and grow into seedlings, but I try to sell my surplus plants as quickly as possible so that they can get planted out. Plants in pots, no matter how well they seem adjusted, will respond quicker and more vigorously when given a chance to develop relationships with a soil's microorganisms. Unless your ground is frozen or beneath a blanket of snow, the best time to plant something is right after you bring it home.