In the Garden this week: Friday December 24, 2010

• Dear Santa, thank you for the pre-Christmas gift of rain. But enough is enough. Water tanks are overflowing, the grass is growing again and we really could do with a return to sunshine and warmer temperatures for the Christmas and New Year break.

• Watch for an explosion of fungal ailments in the humid conditions, especially on tomatoes, cucurbits and potatoes. Roses will also suffer but they can grow out of it whereas vegetables can succumb entirely. It will almost certainly be necessary to get a copper spray on when the weather dries out. If you would rather try baking soda, a level teaspoon per litre is the recommended dose. The big problem with baking soda is that you have to spray a great deal more frequently – probably weekly.

• The wet weather means that you can still lift and divide many clumping perennials even now. Most of them are in full growth, so as long as you make sure they don’t dry out, they will recover quickly. Replant into well cultivated, tilled soil enriched with compost.

• Grapes need thinning out. We keep to one bunch per side branch. More is not better and you can over crop grapes, leading to inferior fruit. Trim back laterals. If they get too heavy, they can break away too easily and you will lose your bunches of fruit. You also want the plant to concentrate its energy on the fruit, rather than the excessive leafy growth.

• If you have not mulched your garden beds and were alarmed at the recent dry spell, this week’s rain has probably raised the moisture levels sufficiently for you to get a layer of mulch on now. We much prefer vegetative mulches which break down and get incorporated into the soil over time – compost, leaf litter, bark or shredded wood waste and the like. Inert mulches like stones, gravel or lime chip do work to keep the soil moist and suppress weed seeds to some extent but they are not suitable for gardens that you want to dig over or replant at any time and they certainly do nothing to add nutrients or texture to the soils. They are best for areas you don’t actually garden and even then, they are a bit of a mission to keep clean unless you have a handy blower vac.

• Keep up with deadheading (basically anything that has finished flowering) and try and stay on top of the weeds which will have been triggered into rapid germination and growth by the rains.

• If you had a problem with silver leaves on rhododendrons last year and haven’t sprayed this spring, check underneath the leaves for something that looks like dirty threads. These are the thrips which suck the chlorophyll out of the leaves. Photinia and honeysuckle both harbour thrips too. If you are going to spray, it needs to be a systemic insecticide so the plant sucks it into its system (as opposed to a contact one which only kills insects where it touches). Bands soaked in neem oil secured around the trunk are getting good reports. If you want to make your own, soak a strip of old woollen carpet in neem and then secure it around the main stem with the carpet pile inwards. Thrips don’t usually go away of their own accord. You either need to change the growing conditions, kill the insects or remove the host plants altogether.