Monday, October 30, 2017

Let's Plant! Tips for Planting and Propagating via Division

Plant Selection

Plant propagation by division is exactly what it sounds like - splitting an existing plant into two or more pieces to replant as new separate plants. For a plant to be propagated through division, it must have multiple stems growing from the ground so that each divided clump can contain both stems (or a portion of the crown which will grow stems) and roots. Division is most common with mature herbaceous perennials, but may also be used with bulbs (what I call lazy lifting), offsets, and plants with suckers or similar.

Although division is a go-to method for large clumping or creeping perennial plants, smaller plants and shrubs that naturally send out suckers to root, such as strawberries and blackberries, are one of the the simplest forms of plant to propagate through division. Runners are are horizontal stems that grow above ground from the crown. Little baby plantlets will set along nodes on the runners and set their own roots, from which the plantlet then matures and grows.  Stolons are similar, but they stretch out from the parent plant below the ground rather than above, popping up baby plants without the visible tether of a runner.  Plants that grow hen-and-chick offsets, like many succulents, have a lateral stem umbilical from the parent plant (hen) that grows an adjoining offset (chick), kind of like a runner but much closer to the parent.  Similarly, bulbs that clump with new bulblet plants developing around the parent plant are also easy candidates for division as they are well-suited to natural separation.

Dividing and Planting

You can divide plants at any time (growing conditions permitting); however, the best opportunity is usually when the plant is not in active growth.  If the plant you wish to divide has a dormant period, the best time for division is usually just as it's about to awaken for regrowth.  Spring and autumn are the most common times for division propagation. Since root disturbance is much lower, there's more leeway for modified division, such as separating runners and stolons from their parent plants by snipping the umbilical and (if needed) transplanting to pots or direct.

Each section of the divided plant must include both roots and crown (or shoots/leaves for suckers, chicks, and other variants).  Rough division cuts and digs out a large plant in smaller clumps that are then immediately replanted. The best tools and techniques will depend on the size and sturdiness of the plant, but its not uncommon for this to involve large digging forks, a spade tipped shovel, or even an axe!  Fine division lifts the plant first for a slightly more selective splitting of the parent plant into smaller clumps. This may involve teasing the plant apart into sections, careful cutting, or a combination of both.  If the plant has a woody crown or fibrous roots, some cutting will usually be needed. If you wish to preserve the size of the parent plant, you can sometimes take small divisions from the edge of the donor parent by splitting them from the parent in-situ using a sharp spade or similar. If you are dividing a mature perennial with a "spent" core in the parent plant, these middle pieces may be nonviable and can be discarded to compost instead of replanting. No harm in trying if you wish (I hate to trow out a possible plant) as you can always pull and compost later if they fail to survive or thrive (see troubleshooting below).

Transplant shock prevention techniques need to be modified for division as, with the exception of modified divisions (runners, chicks, etc.) root disturbance is essential to the separation process of splitting the plant. While many plants cope very well with rough handling for division, the less damage done in removal and division the lower the stresses. While its tempting to go small, larger divisions with ample healthy roots can have better chances of survival.

When planting, the aspect, depth, and other environmental conditions should be well-suited to the type of plant you're propagating.  Prepare your planting area before division if possible so that you can minimise stresses on your plants by replanting as quickly as possible.  If immediate replanting isn't feasible, such as plant sharing or garden works, protect the plants with interim measures as you would any transplant.  Of particular importance, don't let the root ball (or split root balls) dry out during the process. For the short term, wrap the roots until you can replant.  For lengthy delays, you may wish to pot the plants into temporary containers.

To reduce transplant shock, you can use the same techniques as you would for whole plant transplants. Water thoroughly after planting and don't let the new plantings dry out during re-establishment. If the plant you are dividing has ample foliage at the time of separation and replanting, it can be beneficial to prune some of the foliage or cut back the leaves by up-to two thirds to help protect the plant from water losses and encourage the plant to focus on its root system during re-establishment.  If you're a fan of seaweed solution, sugar water, or other tonics, you can try those as well. I always use seaweed solution on my new plantings and transplants.

Plant Care

Once re-established, plant care is the same as the parent plant. Of note, plants that can be propagated through division often benefit from the process of being split every few years. Win win!

Troubleshooting Tips

Divided plants are essentially transplants that get roughed up and split into pieces during the process, so while it's a very easy form of propagation, it doesn't always end in success.  Transplant shock and other difficulties may be encountered with divided plants.

If your divided plants don't survive propagation, review your garden journal notes on plantings and double-check that the varieties you've chosen are well-suited to propagation through division and to their new planting conditions in your garden.  If everything looks good on paper but the plants haven't thrived,  consider whether there have been any adverse conditions during propagation or settle-in that may have compromised the plantings.  Were there any difficulties during division? Did you have trouble digging out the root ball or separating the plants? Did the clumps have enough healthy roots? Did you have any difficulty splitting the crown? It's tempting (so tempting) to overdue splitting in the hopes of maximising the new plants, but larger divisions with ample healthy roots can have better chances of survival, especially if you are autumn propagating before a harsh winter or out-of-season due to other garden works. Were there any delays in replanting or harsh weather, like an unexpected freeze or stretch of hot dry weather while your plants were settling in to their new positions?

If new plantings survive but fail to thrive and there are no obvious issues with variety, pests, or disease, it may be due to adverse conditions during propagation or settle-in (see above) and will hopefully perk up in time, or they may be suffering from other adverse growing conditions in their new home (poor variety for location, low quality soil, poor aspect, over shading, etc.).  Double check your growing conditions and see how things go with time.

If new plantings grow well but fail to impress with blooms and there are no obvious issues with variety, pests, or disease, don't panic just yet. It is not uncommon for divided plants to leaf well but flower poorly in their first year while the plant puts its energy into root development and re-growth.  If this doesn't improve in the next growing cycle, revisit your growing conditions to see if there may be issues with soil quality, shading, etc.

If divided plants were initially performing well but are declining over the years, decreasing soil quality, increasing shade from nearby maturing plantings, or overcrowding may be factors. Some plants benefit greatly if they are divided periodically, as noted above.

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