Succession Planting Success

June 29, 2025

June 2025

 

Succession Planting Success!

A tunnel house is a seriously wise investment, and never more so than in the coldest months of the year. It’s at these times that a tunnel house has the capacity to deliver significant quantities of the sort of fresh produce that reaches premium prices in the supermarket. But only if you make it happen. To make use of every square centimetre of space in the tunnel house over winter, many growers rely on succession planting.

 

What is succession planting?

Succession planting is a gardening practice which ensures successive rounds of crops are waiting in the wings while a mature crop is still being harvested. It means there is constant supply of fresh produce and, just as importantly, that fresh food doesn’t go to waste because of an over supply. How does it happen? Read on to find out!

 

Succession planting techniques

Sow careful

Winter tunnel house succession gardeners sow little and often, taking care to choose the seed of vegetables which would normally grow outdoors in autumn and early spring. Depending on how long it takes for a chosen crop to mature, these sowings can be made between 1 and 6 weeks apart. For example, a fast-maturing crop of sprouting peas or autumn mesclun mix may be sown just one week apart. A crop of red winter lettuce or radish, which takes longer to mature, may be sown 2-3 weeks apart. Large brassica, such as cauli or broccoli, are more likely to be transplanted 6 weeks apart.

 

A second sowing technique is bed-sharing. This method involves sowing the seed of two or more vegetables in the same space. As the faster-growing vegetable outpaces the slower-growing one, it is quickly harvested (at baby stage) by being snipped off at its base. This ensures that there is no root disturbance to the slower-growing vegetables around it. Without competition, the slower-growing vegetables are then left to grow on to maturity, or they, too, can be harvested at baby stage. An example of bed-sharing is the simultaneous sowing of fast maturing Feathers Peas (for sprouts), rapid-maturing mizuna (for a baby leaf), and spinach beet (a slower-maturing green that can be harvested at any stage from ‘baby’, onwards).

 

Intercropping

To make the best use of precious tunnel house space, succession gardeners also transplant or sow individual fast-maturing crops between slower-growing ones. The fast-maturing crop takes advantage of the ‘light-wells’ and soil nutrients between the slower-growing crop, and is harvested before its growth impedes that of the slower-growing crop. As an example, spinach may be transplanted into the tunnel house bed in between space-saver cabbages. Or bok choi can be sown between young celery plants.

 

In the wings

Providing a steady stream of seedlings for transplanting purposes is key to successful succession planting. However, in cool conditions, seedling-raising can easily fail, leaving a gap in your planting schedule. However, there are ways to avoid this happening, where possible.

Plugs and germination pads

Individual seed should be sown directly into individual ‘plugs’ or ‘cells’ of quality seed-raising mix (one seed to one plug). To increase the success of germination, and to speed up root and leaf growth on young plants, tunnel house succession gardeners often rely on germination pads. These pads provide a steady bottom heat that warms the soil. In the winter months,  soil and slow growth is a recipe for diseases such as powdery mildew, downy mildew, and leaf spot, all of which contribute to damping-off (the collapse of very young plants due to fungal disease). The advantages of a germination pad can further be enhanced if seed raising containers are covered with a pane of perspex or (where safe to use it) glass. This covering traps in heat and moisture, while allowing light to reach newly germinated plants. When using a clear covering such as perspex or glass in a sunny location, check frequently that excessive heat does not ‘cook’ young seedlings or raise the temperature of the soil above that which is suitable for germination (use a garden thermometer to test). Seed containers on a germination pad will require regular applications of moisture. If using a spray bottle for this purpose (a good idea, as it does not wash the seeds from the soil), always ensure that you are applying sufficient moisture to penetrate the growing medium down as far as the roots.

 

Container choice

Growing directly into plugs or cells ensures there is almost no root disturbance when the seedlings are popped into the tunnel house bed (the aim of succession planting is to speed everything up as much as possible). However, what these plugs or cells are made of is vital to the success of your succession planting. When working in the outdoor garden, growers often choose to sow into individual coir or peat pots. These pots are then transplanted into the garden, along with their seedling, something which avoids root disturbance. However, in order to quickly break down in the soil, and allow for rapid root growth, these kinds of containers require a high moisture environment. In the tunnel house, especially over winter, moisture is kept at a minimum in order to avoid fungal disease. In this drier, undercover-environment, coir or peat pots are unlikely to break down as quickly as they need to. When they don’t, a seedling’s root growth is impeded. When working in the tunnel house, avoid using coir or peat containers to grow your individual seedlings. Instead, choose plastic cells, and when it comes time to transplant, carefully upend them and gently push on the base of the individual cell to prise out the seedling.

 

Tunnel house bed prep

Succession planting seldom allows time or space for the replenishing of soil nutrients. This is because, doing so, inevitably involves working the soil, something that can damage the roots of plants that are already in the bed. Better by far is to thoroughly enrich the soil at the time when spent, warm-season plants, are removed. Ensure you use a humus-rich, sterilised compost (including slow-release fertiliser pellets in the medium can help extend the life of the bed).

 

Harvest

The success of succession growing relies on regular, efficient, and clean harvesting practices. Always harvest at the first available opportunity so that remaining crops have space to continue growing. In warmer regions, this can mean harvesting an entire plant at one time. In cooler regions, where growth is slower, it may mean harvesting individual leaves as soon as they are useable. When harvesting individual leaves or stems from the likes of silver beet, open lettuce, or celery, be sure to snap (don’t cut) the vegetable off at the base of the plant. This avoids leaving torn or ragged plant material that is quick to attract disease.

 

Succession planting is one of the easiest and most efficient methods of ensuring an ongoing harvest from your tunnel house during the winter months. Adopt it and practise it wisely, and in all but a few very cold parts of the country, succession planting will dramatically reduce the need to purchase fresh produce.