Gardening broadcaster Matthew Biggs reveals how fluctuating temperatures of spring and early summer may affect harvests this year - plus, find out what else needs doing in the garden this week.

By Hannah Stephenson.

As more people continue to grow their own, there should be no shortage of takers for Matthew Biggs's advice sessions at this year's BBC Gardeners' World Live event at Birmingham's NEC.

Biggs, a regular panellist on BBC Radio 4's Gardeners' Question Time, says that the cold, wet weather of late spring shouldn't hamper crops too much, although germination will have been slower.

"Depending on the soil type you have, the cold, wet weather early on will mean that the soil will have warmed up very slowly, particularly clay which gets waterlogged. It has slowed the season down.

"A lot of people sowed and planted early. Many won't have had the germination at the time. But now everything should be germinating quickly."

Seeds sown early may have ended up waterlogged and rotting, or germination will have been erratic. But it's not necessarily too late for a second sowing, he says.

"What happens is that seeds can germinate in a matter of days in warm weather. You can catch up and redress the balance."

The period of warm weather in late March and early April may have led to seeds germinating, but the cooler temperatures later in spring probably hampered their growth, or they may have succumbed to frost.

"Beetroot, radishes and early carrots are generally pretty hardy, but the cold can affect anything planted during the cooler, wetter period. In fluctuating temperatures, beetroot are inclined to bolt."

Tomatoes, runner beans and courgettes shouldn't be planted out until all risk of frost has passed, so savvy gardeners will have kept them indoors throughout the cold, wet spell but should be quite safe to plant them outdoors now.

"The key rule with planting out is to go by the weather, not what it says on the label. It may say, 'Sow from March to May', but if in March the ground's waterlogged or freezing, ignore that advice.

"Weather conditions dictate when you should sow. Instructions on the packet are more of a guideline."

Tomatoes are susceptible to weather-related diseases such as blight, which is related to periods of warmth and humidity at the end of June.

"There are some varieties such as 'Ferline' and Shirley' that have some resistance, but it is only resistance and you can still get walloped. It's more of a problem in wet weather," Biggs says.

"Leaf mould can also be a weather-related problem, while splitting and cracking are cultural problems, caused by erratic watering, as is blossom end rot."

For those growing tomatoes in large pots outdoors, ideally use a multi-purpose compost with added John Innes, which is a heavier, more moisture-retentive compost, he advises.

Grafted tomatoes may also be more resistant to disease, producing heavy crops early on because of their natural vigour.

Those who have sown crops later because of bad weather will have later harvests, he says, but if we now have consistently warm temperatures, they will catch up.

"There are hardy varieties of lettuce, beetroot, early carrots and peas which are bred to grow in cooler conditions. Those early crops are normally the first ones to mature. For the most part, by the time you've had a long growing season, you will hardly notice."

It will be music to the ears of the many vegetable gardeners who worried the growing season wouldn't be long enough to see a good harvest.

"There won't be too much damage from this year's fluctuating temperatures," Biggs concludes.

"Things will inevitably be two or three weeks later, depending on where you are in the country. Colder areas, which have a shorter growing season anyway, may scupper some crops but the damage should be minimal."

:: Matthew Biggs will be hosting Grow Your Own Garden at BBC Gardeners' World Live, June 13-17, at the NEC Birmingham. The show will also feature Monty Don, Alan Titchmarsh, Carol Klein and other gardening favourites. For more information, visit or call 0844 581 1340 Best of the bunch - Allium This ornamental onion, with its eye-catching lollipop flowers most commonly available in shades of mauve, remains a popular bulb choice for gardeners, standing tall in beds and borders in early summer.

It looks great planted among ornamental grasses such as Stipa tenuissima or popping up through leafy ground cover plants like wild geraniums which will hide its strappy leaves, which die off and can become unsightly before the flowers bloom.

In big borders, larger blooming varieties such as A. 'Globemaster' and A. cristophii can be planted singly, positioned randomly through the planting, forming soft balls which seem to bounce along the border.

Smaller, more subtle varieties such as A. azureum can be planted in groups of five or seven and look great at the front of a sunny border with plants such as dianthus and helianthemum. White varieties, such as A. stipitatum 'Mount Everest', are also available.

Bulbs should be planted in autumn, three to four times their depth in the soil, in a sunny, well-drained spot. Leave them undisturbed after flowering and they should come back year after year.

Good enough to eat - Runner beans If you haven't yet planted out your runner beans, you need to do so as the weather should now be warm enough for these tender plants to thrive.

Before planting them, make sure you have supports in place, either in the form of a wigwam made of bamboo canes, or pairs of crossed poles with one horizontal support, or parallel avenues of hazel twigs to give a natural look to the framework.

When planting out your beans, keep them protected from slugs and snails, which love the tender leaves of young plants. If you don't like using slug pellets, protect plants by surrounding them with a collar made from an old plastic bottle.

Water the plants in well and once the flowers set, spray them with water regularly. Whatever you do, don't let the soil dry out completely or you'll lose them. I also plant sweet peas with my runner beans, which attract more pollinating insects, thereby increasing my crop of beans and adding more colour to the vegetable garden.

Dwarf runner beans won't require much staking, although they may benefit from the support of some unobtrusive pea sticks around the plants, to stop them flopping.

In really dry weather, give the plants a good soaking and mulch them with compost or old newspapers. If your plants have gone into well-prepared soil, they shouldn't need extra feeding but those in containers will need a weekly application of liquid tomato feed while the plants are carrying crops.

Good varieties include 'Lady Di', which produce long, slim, tasty beans, and 'Sunset', which will give you a fine crop early in the season.

Three ways to... Be waterwise this summer 1. Use grey water - that which has already been used in the home. Normal household soaps and detergents don't damage plants but avoid bleaches and strong disinfectants. Make sure the water is cool before using it in the garden.

2. Water the roots around the stem base and do it early morning or in the evening, when it won't evaporate so quickly.

3. Even if you have a hosepipe ban, drip irrigation systems are still allowed. Consider a leaky-pipe system to keep parched plots alive. Many modern systems have efficient water usage.

What to do this week :: Check your containers. Hanging baskets and small pots may need watering every day.

:: Thin hardy annuals and vegetables sown in open ground.

:: Feed plants in borders.

:: Sow seeds of fast-maturing annuals, spring-flowering biennials, herbs and vegetables.

:: Disbud border carnations for larger blooms.

:: Cut back aubrieta and alyssum in the rock garden immediately after flowering.

:: Put nets on fruit cages over soft fruit.

:: Complete planting of aquatics if you want a display this season.

:: Cut back stems of early flowering border perennials and deadhead them unless seed is required.

:: Check for powdery mildew and other diseases on plants such as Michaelmas daisies, lilies and peonies.

:: Plant Anemone 'De Caen' corms under cloches for flowering in the autumn and winter.

:: Continue to take softwood cuttings of honeysuckle, jasmine and pyracantha.

:: Plant out autumn/winter cabbage, winter cauliflower, sprouting broccoli and kale started in pots or a seedbed, as space permits.

:: Continue to sow early carrots.