Propagating by division
Although the infertile big blue poppies can only be propagated vegetatively, i.e. by division, it is also a very good and reliable way of propagating perennial species in general. Even though you get fewer plants than by seed, the results are more immediate, and it can often be an easier process than propagation by seed. It is also a very good way of rejuvenating an old congested clump; once it has been carried out it should result in more flowers than if the old clump was left untouched.
There are two main times to carry out propagation by division: early spring (March in the UK), and late summer (mid to late August in the UK). These timings help to limit the stress on the plants due to environmental conditions and give the best chance of rooting and growing on by the divided material.
In early spring it is important that it is carried out a time when the soil is warm, and the plants are just emerging from dormancy and beginning active growth. The leaf buds will be visibly expanding, but the leaves will not be extended, when they could easily be damaged.
In late summer the process is normally carried out in the third week of August. In practice it is best to remove the leaves, as at this time the soil is still warm enough for the plants to root and grow new leaves, before they go dormant in mid autumn.
The procedure is the same whichever time of year you choose, with the only difference being in the spring there is no foliage to remove from the lifted material.
First the clumps are lifted with a fork. It is important that the fork is not inserted too close to the clump as several varieties produce rhizomes that run a significant distance from the clump (notably Meconopsis ‘Ascreavie’ and M. ‘Huntfield’).
If this is done in late summer, it is important to cut back the foliage to just a few inches – effectively removing the full-sized leaves altogether. This helps keep the balance of root to leaf so that the offshoots can put more energy into forming roots than supporting the leaves. The new leaves grow amazingly quickly. They will be fully grown before they die back in autumn.
Once the clump is lifted, it should be then divided by hand as the shoots are very delicate and could easily be killed by being sliced in half by a spade! These clumps can be broken down into lots of pieces with one or two rooted shoots on each piece to produce the maximum number of plants. Even tiny pieces grow, but they may take a couple of years to flower. Large pieces will flower in their first season. Alternatively, you can break the clump down into larger pieces, to give new clumps that will almost certainly flower in their first year.
A large clump (3-4 years old) can easily produce as many as 10 new pieces for replanting, even up to 40. It is very important that these new plants are watered in well once they have been replanted. These offshoots can be lifted again after a few years and the process repeated.