How to distinguish between suckers and seedlings;

• Suckers are growths that appear from the root systems of many trees and shrubs. They may appear in borders, lawns, between paving stones or through paths, and can become a nuisance. Poplars, cherries, plums, stags-horn sumach, lilacs and false acacias all
  Suckers are growths that appear from the root systems of many trees and shrubs such as lilac, cherries, Robinia. On grafted plants such as roses, suckers can grow from below the graft union, on the rootstock material. Suckers are usually removed by gently pulling off when young.

  sucker freely. Suckers from non-grafted plants can be removed when they have roots at their base, to be grown on as an easy and low-cost way to produce more plants. 
• Many trees and woody plants also set seedlings profusely, which can be a good thing, as it generates new plants, but can also become an unwanted nuisance in the lawn, borders and other parts of the garden

A seedling is a young plant grown from seed.

seedlings

Suckers

Suckering is part of the natural habit of plants, and is one way they exploit a favourable habitat, instead of relying on seed spread, for example.

Some trees and shrubs are naturally shallow-rooting; many others may develop roots near the surface due to difficult growing conditions, such as a high water table or impervious subsoil. This makes them more prone to suckering.

Suckers can appear after root damage, resulting from digging or forking around trees, damage to surface roots during mowing, or where roots are accidentally or deliberately severed during excavations.

Seedlings

Seedlings can arise from tree and shrub seeds that drift in the air (ash or sycamore keys for example), are buried by wildlife (such as hazelnuts and oak acorns), or excreted by birds (such as holly or Mahonia seeds).

Cultural control

In the first instance, see if a non-chemical control option is feasible;

• Suckers: Remove suckers as close as possible to the point of origin on the root, scraping away soil to reach the base if necessary. Tear, rather than cut away, the shoot so that the majority of dormant basal buds are removed, thus reducing the possibility of regrowth. In grassed areas where roots are surfacing, strip off the turf and raise the soil by 5-7.5cm (2-3in) before replacing the turf in late autumn or early spring
• Seedlings: Dig out as much root as possible. Seedlings are much easier to remove than suckers and less prone to returning

Weedkiller control

• Suckers: Sever the root to isolate the sucker from the parent tree and then carefully treat the sucker with either stump and root killers containing glyphosate (e.g. Roundup Stump Killer, Doff Tree Stump & Tough Weedkiller and Westland Resolva Pro Tree Stump) or triclopyr (Vitax SBK Brushwood Killer). The health or stability of the tree may be affected if several large roots are severed. If treating many suckers that are still attached to a tree, be cautious, as sufficient chemical may be absorbed to cause harm to the tree. These chemicals may also kill surrounding plants if spray is allowed to drift onto beds or borders. Triclopyr (Vitax SBK Brushwood Killer) does not kill grass
• Seedlings: Chemicals are not normally needed, but you can treat freshly cut surfaces with weedkiller, as for suckers

Removal of the tree may be the only solution when suckers are too numerous. Cut down the whole tree, remove any large suckers on the stump and then apply glyphosate (e.g. Roundup Stump Killer, Doff Tree Stump & Tough Weedkiller and Westland Resolva Pro Tree Stump) or triclopyr (Vitax SBK Brushwood Killer) to the freshly cut surface. This helps to reduce the chance of subsequent sucker development, which can occur even some distance away. Sucker production should gradually decline as the stump and root system die.

Seedlings and suckers typically occur in places that are difficult to access, between buildings and sheds, for example. Here foliar treatment (applying it to the leaves) with weedkiller, using the products recommended above, can be effective, as there are seldom nearby plants that will be harmed. Apply weedkiller in summer. More than one application may be required.

Inclusion of a weedkiller product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener.

Downloads

Weedkillers for gardeners (Adobe Acrobat pdf document outlining different weedkillers available for gardeners; see sections 1a and 4)

Links

Chemicals: using a sprayer
Chemicals: using safely and effectively
Chemicals: using spot and broad-scale weedkillers
Weeds: non-chemical control