I find most general gardening explanations to be either confusing or decidedly unhelpful, rather like the instructions for changing the transmission of my Datsun back in 1980.
The first step in the Chilton manual said only, “Remove old transmission.” The exhortation to ‘repot when necessary’ is just about as helpful if you’ve never done either job before. Sure, I figured out how to drop the trannie, and got the car rolling again in time to go to work Monday, but it wouldn’t have hurt them to draw me a map. That’s what this column really hopes to be – a map to why and how to repot.
A plant needs to be repotted when
• Roots grow out of the drainholes or heave out of the soil surface, as in the photo with this column.
• Pots crack or break as roots push for more space.
• Pots drain water very rapidly, indicating crowded roots in proportion to soil.
• Pots dry out overnight or topple over when dry because they are too small for the plant’s top growth.
• Pots do not drain, water puddles on its surface.
• Soil pests such as gnats or ants have been an issue.
• More than 2 years have passed since the last time you repotted. In this case, the potting soil needs to be rejuvenated and the roots may need pruning on specimen plants kept in the same large container for years.
I’ve often read, “Anything can be a container”, if it has a hole so water can drain. Truth is, some things make good containers. But if you’ve ever tried to grow vegetables in big black nursery pots on a concrete driveway in Baton Rouge, you know there are limits to the list of wise containers. Yes, the vegetables grew well, but the heat that built up in the soil dried it out badly and every one of the 20 pots had to be watered twice daily!
The Big Idea in repotting is to make ample room for roots to grow and thrive without encouraging them too much. If you move a plant from a very small pot to a very large one, two problems can develop. The roots may grow to excess at the expense of top growth, and/or the soil may stay too wet for new roots to develop. A good rule of thumb is to move that plant up to a pot not much more than one inch bigger around that its current container. Since the idea is to transplant with as little damage to the roots as possible, break the pot if necessary.
You can push on a plastic container to loosen the roots, but rigid plastic may not ‘give’ and roots can become very tightly packed, too. If needed, cut that container off to avoid crushing the roots. You’ve also got to leave room to water the pot efficiently, about an inch from the top of the soil to the top of the pot (called headspace). Put the plant into its new container at the same depth it was growing, allowing for headspace. Whenever you water a plant, fill the headspace and let the water percolate through the soil to exit the drain holes. On hot summer days, water outdoor containers with another step: refill the headspace again after the water has passed through the first time. Add fertilizer on the second pass to prevent watering it right out of the pot.
Good potting soil does come in bags, but if you’ll add half its volume in ground bark, the resulting mix will fill large pots for dramatic mixed containers. Amplify the mix with another amendment: add compost equal to half the original volume of potting soil and a cup of lime per 2 cu ft of potting soil, and you’ve got a good vegetable-growing medium.
GardenMama Nellie Neal is a writer, photographer, and radio host whose new book, Organic Gardening Down South, will be released in September, 2008, by BB Mackey Books of Wayne, PA. She has been a member of Garden Writers Association since 1993 and is National Spokesperson for Multi Bloom and Mega Green, OMRI listed organic catfish hydrolysate fertilizers made in Isola, MS. Her website is www.gardenmama.com.